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Food for thought: A couple of years ago I heat treated a batch of bamboo in my convection oven for 2 hours at @ 250, an additional hour at 325 and then because the color was not dark enough, another hour at 400. The temperatures were verified with a probe type thermometer. Needless to say, the color of the bamboo was a very deep brown such as French Walnut. The strips were glued as a nodeless 5’ 4 weight. The attempt to spiral the rod was a failure because the jig allowed about half the rod to unwind before the Epon set. One day when a nonbeliever questioned the strength of bamboo, I grabbed the 5" section and bent it into a full circle. The tip touched the butt momentarily! It not only did not break but the next day it was straight. Encouraged I sanded it to a round shape to hide the partial twist and taped some guides on for a trial cast. It really was A-OK. The rod was finished with salvage components and given to a friend who fishes it often. Since that time several rods were built using the 400 degree treatment to obtain a darker color. Alternating light and dark strips makes a nice contrast. There has not been a failure or a set. Another observation is that these rod are not wimps. Where does that leave me in this debate? I like the color. (George Rainville) This is going to sound kinda silly coming out of someone who generally looks at everything from an engineering standpoint, demanding statistics and studies before he'll change the way he does things, but I have a little different regimen for heat treating. I guess I've done so many rods that there's one thing I've learned to key in on when it comes time to heat treat. Oh, yes, I have a temp and dwell time routine that I "try" to stick to, but for some reason, that just doesn't always work, although sometimes that "thing" that I key in on occurs just as the bell on the timer rings (rare event, but it does happen). Maybe the differences from session to session are effected by ambient temp, ambient humidity, or the differences in properties such as power fiber density, internal oils and moistures of each individual culm, or maybe it's just plain bad luck, but every rod heat treated for the same amount of time does not come out the same! They may be close, but I've learned, at least for me, that I have to deviate slightly from my "standard" heat treating time and be aware of something else going on... OK... here goes!!! (Why do I feel like some of you are going to laugh at this, and others going to dish out unmitigated hell for it! LOL) I do is stay right there with that oven, watch that timer, and inevitably, within a minute or so either way of my target time, my NOSE tells me it's time to take the cane out. Yup, Mr. Engineer relies on "smell", in conjunction with temp and dwell time... of course, those of you that know me, know that my nose is rather akin to that of an aardvark (those that don't know me, picture a bald headed aardvark with a beer belly!), so maybe it is, by nature of it's size, more in tune with what the cane smells like when it makes that magical transformation where the properties change. Now, it took me quite a few years to notice that the aroma of the cane "changed" at some point during heat treating, and, yes, I heat treat no less than 3 times each month, so maybe it's not something you would key in on if you only make 5 rods a year, but it works for me. I know!!!!! I'm one of the worst ones to get on here and want something proven to me scientifically. Data and statistics, with control groups, etc, etc, etc, and now here I am telling you that I can SMELL when its time to take the cane out of the oven! Keep in mind that the smell I look for almost always happens within a minute of my standard heat treating time, usually less than that. (Bob Nunley) Hi, Bob - it's not surprising that you are using your sense of smell to determine when it's "done enough." Coffee testers, who taste coffee for the coffee companies, rely heavily on their sense of smell to determine when the coffee has been roasted the exact right amount of time. Wine experts rely primarily on their sense of smell in determining the quality of a vintage. Beer experts (such as at the Great American Beer Fest in Denver (?)) also rely very heavily on their sense of smell to tell them if a beer has been brewed long enough, had the right amount of hops, the correct yeast, etc. The real trick is for you to transform the information your nose tells you about cane to something the rest of us with uneducated noses, or no sense of smell, can use - such as a time/temperature regimen. Or, maybe a really good description of how the cane smells to you during the treatment; for example: "it starts out smelling like wet cane, then progresses to a smell similar to ironing linen, and then just as it begins to smell like a hint of caramel popcorn, it's done" or whatever the actual odors are. (Claude Freaner) It makes a lot of sense to complete the heat treating process this way. Pressure, temperature, your thermostat or thermometer, moisture in the air, moisture in the cane, cool spots in the oven, there could be a million variables. I think the best scientists must question there measuring devices and use their senses (and common sense) as the final test. Now I know the source of your recurring comment "Sorry, it must be the fumes." (Bob Maulucci)
The recent tests and discussion on saturation has caused me to ponder some other questions. For heat treating the consensus seems to be 325° to 350° for 10-20 minutes Drying may be in the range of 200° to 250° for a couple hours or 100° for a longer time. Wayne states in his video that he has measured the discharge from his heat gun at about 500° but I wonder what the temperature of the cane is then. In other words at what temperature does the bamboo become flexible and soft enough to straighten? I guess what I am leading up to is to develop a heat treating regimen to accomplish a number of objectives. For those of you that have home brewed kinda a step mash. For instance maybe heat for a period at 225° to drive off moisture, raise the temperature to 350° to heat treat the cane and then, since the strips are bound and hopefully near straight, maybe bring the temperature back down to a lower temperature for a period of time to allow the lignin to slowly solidify. Any of that make sense? It just strikes me that several things occur when heat treating and that there are optimum temperatures for each. (Tim Wilhelm) When you bind up your strips for heat treating (good and tight) and treat at 375 degrees for 8-10 minutes, all the bows, sweeps and twists are gone when you take the string off. The strips lay nicely in the forms for final planing. At 375 degrees, don't go over 10 minutes unless your strips are really large. Just cook until you like the color. (John Long)
I would like to ask for your input if you would be so generous. Approximately 6-7 years ago a friend in the heating/air conditioning business made me a simply beautiful oven shell, 2" of insulation all around including the ends, simply marvelous steel mesh sliding cage, this thing is really nice. In fact, it looks almost identical to the nice ovens Bret produces except perhaps just a tad larger and more insulation. I wired it up with oven controls and mica strip heater from Grand Technologies. Inserted thermometers ca. 6" from each end and in the center. The oven takes considerable time to heat up, perhaps an hour to come to temp of 375. There is a ca. 40 degrees F discrepancy from middle (M) (hottest) to front (F) and rear (R). I have tried two different and new mica strip heating elements and still get the central hot spot. I used the oven a couple of times, discovered the overcooked middle, and put it in a corner for the past 5 or so years. Each day I eye the oven wondering what I can do to make it useful (besides storing dried cane strips!). Any advice on what I am doing wrong? Test chart (below) for both mica strips came out almost identical.
If necessary, please respond offlist. I'll take any help I can get!! (Jaz) I had the same uneven heat problem and solved it by installing my heat gun into the oven in addition to the strip heater. It blows heat into the oven and has an exhaust vent to keep the air moving and vent the hot air. A piece of flexible steel tubing carries the hot air from the heat gun into an aluminum tube which in turn carries the hot air to the far end of the oven (the tube extends to within 2" of the end of the oven) and the exhaust hole is adjacent to the heat gun flexible tubing entrance. This method allows the heat gun to keep the air moving and since my heat gun has very flexible heat ranges after an initial set up the heat range within the oven can be kept very constant. (Jack Follweiler) It sounds to me as if there are two problems here, slow heating and uneven heating. I don't have a mica strip oven, but it seems to me it should come to temperature sooner than that. I know Ron Barch's oven doesn't take that long to heat. I wonder if the cord is heavy enough wire? It should be AT LEAST #14 and # 12 would be better. (#14 is rated for 15 amps, #12 is rated for 20 amps.) Also, oven should be used close enough to the outlet that you don't need an extension cord. The uneven heating could be fixed by installing a fan of some sort, or using a heat gun as someone suggested. (Neil Savage) I don't have a mica strip oven but wonder whether using some sort of heat sink or ballast such as sand around the strip might not even out the temperature. Seems like I read something about this in the past. Oven will get pretty heavy pretty quick, but if it doesn't need to be moved around it might be worth a try. Sand ain't expensive. (Barry Mayer) Judging from the comments on this list and friends I've spoken with many experience the problem of uneven heating with mica strips. At its worst you end up with strips charred in the middle and hardly discolored on the ends. A big problem. Jack and others have suggested adding a heat gun to circulate air in the oven and even out temps. Others suggested using heat shields or heat sinks. All great suggestions. Another problem with my oven is a long recovery time. So that it's simply not possible to maintain an even temp within ± 5 degrees or even 20 throughout a heat treatment period. Even if I start with a preheated oven at say 375, once I introduce three bundles of strips the temp drops rapidly. But I still think it's a great design, inexpensive and easy to assemble, and it will work fine once you learn the quirks. I solved the uneven heating with a few techniques. I preheat the oven for about 1.5 hours to eliminate any cold spots and even out temps. (Shop temp is about 60). I monitor the temp with an inexpensive stem thermometer in the center of the oven where the oven is hottest, and ignore temps at either end. (I've never calibrated my thermometer and my temps, given below, may need to be adjusted given your conditions.) During heat treatment of strips, I avoid temp over 365. Given my conditions, I know that at 375 I'll get charring and it's the high end temp that produce this problem. (Again, given different tools, your high end temps might vary, but the principle is the same. Monitor temps at the hottest part of the oven and avoid the high end that produces charcoal.) Once you introduce the strips into the oven, the temp drops fast so I start with a relatively high temp to begin with, like about 375, because I know the strips will never reach this temp. I stick with an 18 minutes heat treatment and turn the sections at 9 minutes The time never varies, but the on/off temps do. In order to maintain some consistency of results I decide before hand on my off and on temps, and these temps vary based on the size of the rod or number of sections. For example, here are the result of heat treating an 2/2 8’ 6 wt rough planed to the largest dimension plus .05. This produces a light to medium honey tone, for an even lighter color, I'd subtract 5 degrees from the on and off times. Recipe: Add strips at 375 with thermostat off. Turn on at 345; Turn off at 350.
Given my conditions, this is a typical heat treatment. I look for a pattern of temps that is about the same, but the initial drop in temp varies depending on whether the mica strip is in a heating or cooling cycle when I first introduce the strips, and so the times when I actually turn the thermostat on or off vary. Just look for a pattern that is similar, or similar mean temp. You'll need to establish the best on/off/entry temps for your conditions and the results you prefer, but the principles I've outlined should work fine. So now you know why given my experience a simple recipe like "bake at 3xx for y minutes" never made sense to me, and don't quite understand how it made sense to anyone else. Ovens don't really work that way. (Bob Milardo) Since I have built the heat gun oven, I have never had the problems that people seem to be having when heating with mica strip heaters. The oven that I built using two heat ducts and a heat gun give me very consistent temperatures in the five foot sections. I have a thermometer at the top and bottom of the outside section and the temperatures never varies more than 2 or 3 degrees. I put the temp control of the heat gun on its highest setting to bring the temperature up quickly to 370 degrees and then adjust it to keep it at this temperature. I heat treat at 370 degrees for 30 minutes and the nice brown color is consistent throughout the whole section. I have never had a problem with burnt strips or charcoal. The oven is cheap to build and the most expensive part is the heat gun (Sears) that I also use for nodes and straightening. (Tom Bowden) I second this. I built Jon McAnulty's oven (see this link). The ease of construction and uniformity of the heating are a real plus. I did melt a bit of the plastic casing on my heat gun the first time I lit it off, but I learn well from mistakes. (Gary Misch) Just a thought, try placing some sort of heat shield over the middle of the heat strip. Maybe some sheet metal or some high temp insulation. Just a thought. (Joe West)
I was fooling around with heat treating this past week and decided to collect information from as many sources (books, notes, list data, etc.) as I could to see what folks used for nominally heat treating bamboo. So I looked at all the sources I could find plus a few data points that I have picked up off the list. I had 11 pairs of data points from names such as Anderson, Byrd, Garrison, Tefft, Cattanach, Gould, Nunley, Boyd, Schneider, and Maurer extracted from books or from discussions on this list. I assumed (probably bad, but engineers always make assumptions to solve problems) that these reflected a variety of heat treating recipes from blond to well cooked rod sections. Too make a long story short, the mathematical model for a best fit linear regression analysis of the data is: Temperature(DegF) = - 4.9 * Time(Minutes) + 414 This is a simple linear equation that looks like it agrees quite well with the data scatter and it makes technical sense. The data I used varied from temperatures between 250 and 400 degrees F with times ranging from 30 to 6 minutes respectively. Most of the data points were clustered in the 7.5 to 20 minute and 375 to 325 Degrees F temperature "box". One can use this linear model to provide some approximation to acceptable Temperature vs. Time bamboo cooking times. If anyone has data they would like to share, I am willing to add it to the current model and update this initial model approximation. I know this will help me as I decide my cooking approaches for bamboo. (Frank Paul) Why would this be better than simply picking a number out of the air? I mean, let's say Garrison used a specific temp/time combination and 70% of folks are influenced by Garrison (as opposed to doing in-depth study) wouldn't this skew the data. (Jim Lowe) I agree with Jim that this relationship could be heavily influenced by what various builders have read or learned from one another. I would think that folks would intuitively add more time if they wanted to cook at a lower temp and vice versa. This would in turn potentially produce a linear relation. You could probably do a simple X, Y scatter plot and identify outliers who are builders that like to do their own thing and never listen to anyone (we could probably predict them a priori). Those that are devotes of Garrison or Cattanach should cluster around their respective guru's time and temp. (Larry Puckett) How do your numbers tally when using convection heat versus radiant heat? (Mark Wendt) Mark has a point about how numbers tally when using convection heat versus radiant heat. For the same required cooking time convection ovens will require approximately 25° less temperature than a radiant heat oven. Another way to look at it, convection ovens cook faster than radiant ovens set at the same temperature. (Don Schneider) Thanks for all the responses and interest in my modeling effort. Your suggestions and comments are most appreciated. I have spent some more time this afternoon fooling around with the data and model. First, let me answer some questions that have been asked. I took data from where ever I found it - mostly books, but some data I extracted from the list over time. There was no consideration to whether the bamboo had been flamed, whether the oven had forced air, the oven heating source, oven size, bamboo length, or when the bamboo is heat treated in the making process. As an example, my oven is not a convection type, but an insulated metal tube wrapped in nichrome wire with a set point temperature controller. The temperature is very uniform (+- 2 Degrees F) over 5 feet of its length. Most book authors provide a time and temperature data point, sometimes they suggest a combination of two temperatures and times - in this case I "kind of averaged" the data to a single data point (one case only). The model that was sent to the list had 11 data points, not really enough for a good regression analysis, but it can provide a target range for heat treating bamboo. Here are twelve pairs of data that I used for 3 different models [temp, time]. These data are as follows in pairs. [400,6; 375,8; 350,7.5; 350,10; 375,10.5; 350,11; 375,12; I have built 3 models based on the first 10, then 11, then 12 data sets. You will note that there are two pairs of data that are the same (not sure these are not from a similar source). Matlab was used for doing the calculations. Model 10: temp(degf) = - 5.4 * time(minutes) + 417.3; Model 11: temp(degf) = -4.9 * time(minutes) + 414; (This is the one I sent yesterday.) Model 12: temp(degf) = -4.96 * time(minutes) + 416.5; The mu's are the means; J is the residual squares; S is the square of the deviations; r2 is the r-square value. Ideally, a perfect agreement means J = 0 and r2 is 1. So if you look at the r2 value you will see that as it gets closer to 1, it provides a model that agrees closer to the data used. J is a measure of how much the data spread is left unaccounted for by the model, while S is an indication of the data spread around the mean. As r2 gets closer to 1, J and S become smaller. While these models provide a guide for setting times and temperatures for cooking bamboo, they will not be correct or useful for everyone. They do provide some guidance to new bamboo rod makers (such as myself). To create models that are more predictive, one needs lots more temp-time data. If one has enough data with appropriate limitations (flamed, oven type, etc.) then one could probably develop a reasonable model for say - flamed rods, blond rods, browntoned rods, etc. More thought would be needed to whether this would provide any significant guidance for the heat treating bamboo process. I hope this helps explain a little more of what I was doing with my models. (Frank Paul) Did your calculations take into account the initial moisture content of the cane. Seems necessary if you are trying for a temp/time that will give a certain color. I would assume the color change is due to internal temperature, IE: the cane turns from light tan to dark black (burnt) as it starts to reach a carbon state sans gases which would include water vapor. To truly get a correct temp and time at which a certain color is attained I would think you would need to start with a set standard, A sample of cane of the same size and density with the same moisture content each time. (Saunder Hutchinson)
I thought I’d share this email I sent to Jim Bureau. I would like to hear from anyone who can corroborate of condemn this data. I’ll be off list Thursday afternoon (Gone fishin’) so response from me may be delayed. This is probably not new ground but I didn’t see much in the archives and I don’t own any of the various texts on bamboo rods. (Al Baldauski) -----Original Message----- From: Al Baldauski Subject: Heat treating bamboo samples Jim, Some time ago we talked about the possible differences in bamboo characteristics due to different baking treatments. Well I finally heat treated some strips, put together some hex sections and conducted tests. Here are the results: Bake Schedule First All Samples baked 230 degrees F @ 2 hours to dehydrate Ultimate Strength Test Then: MOE Stress at break #1 230 degrees F @ 2 hours 3.67 x 106 921,113 57,570 Heat treated strips assembled into hex sections with epoxy, room temp cured, then heat cured at 230 degrees F for 2 hours. The results are shown above with the heating recipes. Observations: 1. This is not an extensive group of samples 2. Care was taken to ensure all samples were fabricated and tested equally 3. Modulus of Elasticity measurements were conducted before and after heat curing the epoxy and they were the same except for sample #1. It had a an MOE 20% lower before heat curing 4. The failure of sample #1 was a clean break at the point of highest stress. 5. Samples #2,3,4 delaminated starting at the point of highest stress Conclusions: 1. There is little difference in mechanical properties for samples heat treated above 300 degrees F 2. The glue is the weakest link in a rod made from bamboo heat treated above 300 degrees F 3. The breaking stress is about 4 times greater that the rod stresses calculated by various “Hexrod programs 4. The stiffness of rods made using recipes #2,3,4 will be virtually identical if made from the same culm. Wow Al that was a neat test Now with the questions.. Was that Epon? How wide were the sticks? How long? Was this primarily a test of glue heat setting or of tempering? The stress capability of the cane was good to know. I would like to see the results of a tip, say a .070 section. Is this easy to repeat? (Jerry Foster) All samples were glued up hex sections measuring 0.255 in. across flats and about 7.5 inches in length. Given the nature of my testing, an 0.07 hex section would be too thin to evaluate. The spring force from a typical dial indicator would cause too much deflection on a section that thin. In any case, I don’t think the results would be substantially different. You would have a greater percentage of power fibers in an 0.07 in section but in a thicker section the lower density of power fibers occurs in the center where there is little effect on the outcome (consider hollow built rods). I used EPON but the purpose was to evaluate the mechanical properties of bamboo. The interesting byproduct was the discovery of the failure of the epoxy joint at the midline of the section indicating the shear strength of the glue is lower than that of bamboo, but not by much, since in sample #1 the bamboo failed. In all cases the stress was greater than typically found in the rod during use. (Al Baldauski) Thank you for sharing your data. I did a bit of testing like this about five years ago on rectangular single strips, and one of the things I encountered has not been described by other experimenters. I termed the phenomenon "creep". It could be readily seen during beam bending MOE measurements in nonheattreated samples under fairly heavy stress (similar to the Garrison maximum). While measuring beam deflection with an indicator, I always began with an unloaded beam to record the zero deflection. The load was then applied and a beam deflection immediately appeared which I recorded. However, as long as the load remained, the deflection would continue to increase for several minutes, if I allowed it. I associated this creeping deflection with a permanent set in the beam inasmuch as the beam usually did not return to the original "zero" deflection. I wonder if you too encountered this effect and had to modify your experiment because of it. (Jim Utzerath) Oh yeah, on sample #1 which showed an improvement in MOE after heat curing the epoxy. I attributed that improvement to additional heating of the bamboo. It would seem that a LOOOONNNNGGGG time at a low temperature could improve the stiffness. Would it ever be as good as at higher temps and shorter times?? Subject of MORE testing. (Al Baldauski) Great work. Seems like you have some very useful data for this list. I assume you were able to do this at your place of employment as the email came from Omitech. What kind of test did you use to get the fracture strength - tension or bending? Did you measure the strain to calculate the effective section MOE or how was MOE arrived at? Did you have a testing machine to measure load versus strain? How fast was the test conducted - very slow loading or faster loading and just measurement of the end points - fracture strength and strain? Like to know if the data is available if strain was used. Hope this is not to many questions. An old mechanical engineer who is interested in the mechanic properties of bamboo would like to know. (Frank Paul) The email was from work but we have no mechanical lab here. Unfortunately, my test were done at home using a simple cantilevered beam for testing since it was the easiest to apply a load, especially for the break test. I first measured data for MOE with a dial indicator and a fixed load to give about a 1 ½% deflection of 0.255 inch hex sections at 5 inch span. The load was applied and measurements were taken quickly so that the beams returned to zero deflection within 0.001. The break test was rather crude: I clamped each section onto an aluminum square-edged plate to minimize the possibility of the bamboo crushing into plywood of my test bench. I cut a shallow notch 5 inches out on the beam to hold a loop of nylon cord. I hung a five gallon pail, preloaded with 16 lbs of water, in the notch and over about ten seconds added more water until break occurred. Then weighed pail plus water to within one gram to determine the load at break. Sure, I should have made multiple sections to determine repeatability, but that’s for a more extensive test. Of course, these results are for one section of one culm. Results will vary from culm to culm and from section to section. I’m sure most of you have found that one “soft” section in the middle of a strip. Interestingly, I made a sample section from a different culm about two years ago which was 0.300 flat to flat. When I measured if for MOE I found it to be nearly identical to samples #2,3,4. (Al Baldauski)
The strips for my second rod are ready to be heat treated but I need to dry them first as they were soaked prior to displacing nodes. I dried my first rod strips at 125 for several hours but I would prefer a faster option if possible. Seems like I read that 225 for an hour would do the job without prematurely hardening or darkening the cane. Any thoughts on this? (Wayne Kifer) Give the strips 3 days to dry. If it is humid where you are stick them in a light box. The heat treatment techniques assume we are starting with dry strips. After your strips have dried, you can heat them at 225 degrees for an hour or 2. Then 350 degrees for 20 minutes usually works out well. I am not familiar with how you are heat treating but be careful and let color change be your guide. Keep a strip that hasn’t been heat treated for comparison. Also do some test runs before doing the real thing. (Adam Vigil)
I have everything rough planed and ready to heat. I constructed a heat gun oven, somewhat like the Neunemann design. I used double wall, zero clearance wood stove, insulated chimney pipe, attaching a 2 Ft section to a 3 ft section totaling a 5 foot oven. The end is capped and insulated also. This is well insulated chimney pipe with a central 3" pipe attached to the inside roof of the 6" 5 ft length. Two thermometers show good temps consistent in the 350 degree range (I could get it higher if I wished). I've checked the archives and if there is one topic with so much variation in theory it's the temp/time heating issue. It all seems so anecdotal. OK, in this situation, what would be recommended for temp/time? 1). Non prior flamed cane, blondie 2). Rough planed and bundled, oven ready 3). Neunemann style heat gun oven, well insulated (Mike Valla) Some of us are using a precision, consistent heat treating regimen. You do need a computer controlled oven that will hold the oven temperature within plus or minus 1º F (or C for our metric friends). And generally, that oven will need to be a convection oven. My PID controlled convection oven will hold the temperatures to that kind of tolerance. Using M-D's fixtures, and heat treating to 360º for 30 minutes, I know that my heat treated strips will come out of the oven the same every time. My regimen is a tweaked version of M-D's original regiment, designed around his heat treating fixtures and the consistency and accuracy of a PID controlled convection oven. The strips, mounted on the fixtures, are set into the oven while the oven is cold, and the oven is brought up to the set temperature of 360º F, and held for 30 minutes. After the 30 minutes, the set temp is reduced to 225º F and the timer is reset for one hour, to drive off any residual moisture. I also machine rough bevel all my strips to .250", to keep the heat treating consistent for each piece of cane. (Mark Wendt) The stress curve IS the taper. So.. each of has our own heat treating regimen, as long as that is a constant for each rod, as Mark suggests, we should be able to deduce that up to this point every maker has produced consistently processed cane. So now at this point we throw up our hands and generalize the taper. Or do we do the best we can do. If we knew enough we could probably build a compensation factor to differentiate between DH's method and yours. One does not have to be anal to be curious. (but maybe it helps). (Jerry Foster) "A taper can be directly derived from a stress curve, or, a stress curve can be directly derived from a taper. Therefore they are equivalent. Neither is the rod itself." I would suggest from an engineering viewpoint that your first statement is correct, but they are not "equivalent". That is say that apples =/ oranges, where = means equal. I think you mean to say that they provide a functional relationship but not equivalency. [Inches, centimeters, etc] =/ [PSI, ounce per in square, etc.]. Hope this helps. (Frank Paul)
At what temperature and for how long do you heat your strips to dry them out before really heat treating? I ask because for all my previous rods that I've soaked I've just let the roughed strips air dry for a couple of weeks before heat treating. This time I need to move a little faster and would like to heat treat and final plane right away. (Aaron Gaffney) I use a PID controlled convection oven, with the strips bound to a set of M-D's fixtures. With that setup, I put the bound strips into the oven while cold, and bring the oven up to 350 degrees and hold it for 30 minutes. Then, using another of M-D's methods with a convection oven, I do a step cool down to 225 degrees and hold that for an hour. Note that this method is recommended to be used only with a tightly controlled convection oven, and the aluminum fixtures. It's a regimen worked out by M-D after he designed the fixtures, and I've used it since the beginning. I believe it's best to keep heat treating to a constant, which is why I don't taper my strips before heat treating - the same sized strips see the same amount of heat for the same amount of time. I usually rough bevel and heat treat the same day, after pulling the strips out of the soak tube and straightening and pressing nodes. (Mark Wendt) Thanks for the info. Sounds like an ideal process, also sounds beyond the abilities of my basic mica strip oven. I'll keep it in the file though in case I ever upgrade the oven. (Aaron Gaffney) I will pass on this info as I have been soaking for close to seven years. I soak for at least five days. After rough planing, I use MD's fixtures and set my oven for 125 degrees. Put the fixtures in the oven and crack the oven door open a bit so that the moisture can escape. I check the opening from time to time with a small mirror. When I don't see any vapor on the mirror, I assume that the strips are dry. The fixtures are then removed from the oven and the thermostat set to 450 degrees. I have a small red light that goes off when the heat strip is off. When the light goes off, I install the fixtures with the strips. The temp will drop and the light will come back on. The thermostat is reset to 375 degrees and the timing begins as soon as the light goes off again. I heat treat for 12 minutes @ 375 degrees to get the honey color I like. If I am doing flamed strips I only heat treat for 7 minutes. This is my regime with a heat strip oven. (Tony Spezio)
Regarding the group that uses the 225 degree heat treating time at temp cycle, does anyone care to hazard a guess as to WHY they have adopted this method? Or would that push the envelope on the "They do it that way, so it must be right" school of logic? (Wayne Kifer) I did notice that they also were flaming their cane in the video although it did not appear to be a very aggressive flaming. I was hoping someone more familiar with the old Winston shop practices might comment on this as well. (Larry Puckett) The low temp treatment I have heard of is 24 hours at 200°. The theory is that heat treatment at high temperature causes the moisture trapped inside the cells to boil and steam, rupturing the cell walls and damaging the cane. Therefore, the cane is kept just below the boiling point, and the long time assures that all the water will be driven off. Rods so treated exhibit no color change, and are the ultimate blonds. I have never experimented with this, and don't know if the permanent moisture content reduction effected by the high temp treatments results. (Tom Smithwick) If I read it correctly, Schott's paper implies that low temp long time treating doesn't provide the permanent water loss that higher temp does. But having said that, he also concludes that the benefits from higher temp treating amount to no more than about 1 1/2 %. And that may go away with longer time. My own experiments with MOE showed big gains immediately after heat treating but three days later the MOE dropped by as much as 50%. (Al Baldauski) That's pretty much my conclusion as well, except that his conclusions were based on the time frame he was using. Remember his tests were conducted with a slow but steady increase in temperature through the test. Accordingly, it does not conclude that the final small percentage of water loss from the cell walls, which we have attributed to the permanent tempering of the strips, cannot be accomplished at temperatures as low as 212 degrees given sufficient time. My impression was that Schott felt that the extended heat treatment that the lower temperatures would require would likely be more harmful than faster treatment at the higher temperatures he suggested. However I also suspect that the lower temperatures he was discussing were quite a bit higher than the boiling point of water. I'm going to have to study it more to determine at exactly what lower temperature he considers long term treatment to become harmful. (Wayne Kifer) Water boils at 212 degrees so heating it to 200 degrees will only make it warm water. It will not be driven off at that temperature. If you watch the video they show the temp gauge on the oven and it definitely is pegging 225 degrees. (Larry Puckett) Free water, the water in the cells, will evaporate. It doesn't need to be driven off. Only bound water, the water in the cell walls needs to be driven off at higher temperatures. (Wayne Kifer) Water does boil at 212, but did you ever look at a pot before the water boils. There is vapor coming off. As you heat water, its vapor pressure increases until it equals that of atmospheric pressure, at which point you see the bubbles. Increased vapor pressure means the water evaporates quicker. Water in a dish goes away slowly at room temperature. Water in a warm pan evaporates faster. Boiling water evaporates the quickest. So water in a rod evaporates even if the temperature is below 212, it just takes longer. (Al Baldauski) As I recall, the Paul Young rod company advertised the fact that their ring of fire (read circular gas jet torch) was superior because it drove off moisture instantly. They claimed that the slower heat methods used by other makers damaged the cane as the water expanded slowly. Does anyone else remember this or am I just having my first senior delusion? (Jeff Schaeffer) Yep, He used pentane gas and claimed that it was indeed the best method of curing the cane. They had pictures of him drawing a culm through the ring of fire on one of the web sites and it was about the most consistent and uniform color that one could hope for on the portion of the culm that he had already pulled through. (Will Price) I have an original PHY catalog that Jack Young gave to me many years ago I will look to see exactly what it does say about that. (Bret Reiter) It sounds like "marketing" to me. The "ring of fire" probably did a good job of tempering the outer power fibers where the highest bending stress occurs. Most of the inner material is planed away and is inconsequential. Additionally, as Milward and Schott have shown, the inner fibers have a lower MOE and a much smaller effect on total performance. As far as rate of moisture release: it seems the generally accepted wisdom for drying anything is to do it SLOWLY, but that's mostly to prevent warpage. Since we start with bamboo which is near equilibrium, I don't moisture removal rate is critical. (Al Baldauski) Seems to me at that temperature they're just drying the cane, not heat treating. (Mark Wendt) Ok, the next question to consider would have to be, what would be the benefits of, if any, to low temp heat treating as apposed to high temps? (Wayne Kifer) I agree that low temps can rid the cane of free water, but I still fail to see how temperature less than 212 degrees can break out bound water. It is not so much a drying process as a chemical conversion.. Am I so far off?? (Ralph Moon) I believe it is more than an issue of getting above boiling. There are chemical changes that occur that release water as a byproduct of the reaction, although it wasn't in the form of water before heating. It is analogous to baking, if the oven temperature is too low, the ingredient won't bake, no matter how long they are left in the oven. (Bill Lamberson) Right Bill! but the change is irreversible whereas free water driven off can be regained just as readily. (Ralph Moon) Exactly! Furthermore, it is the removal of this water from the cell walls themselves that makes this process irreversible. Reintroducing water will not reconstruct the original chemical compounds that the cell walls were constructed of. (Wayne Kifer) Some have speculated and/or know of the chemical changes occurring in heated "wood". I'm not a chemist but I do know some changes are reversible and others are not. The small "permanent" change Schott found seems to be attributed to the irreversible heat induced "double bonding" accompanied by "generation" of water by the release of -OH groups. I interpret his explanation to mean that this begins to occur near that steep "knee" in the strength vs temperature curve where relatively small increases in temperature and/or time lead to a snowballing effect which quickly produces charcoal. His "safe" temperature was 200C (392F), one which few exceed in their baking regimes. Below that there is virtually no permanent water loss. (Al Baldauski) This is a bit long in coming but I wanted to spend more time on Dr Schott's paper before replying. I did want to respond as I was interested in your observations relating to the irreversible heat induced double-bonding you mentioned. This double bonding, as well as molecular cross-linking have come up occasionally in the past and I've been wondering where this theory originated? (Wayne Kifer) There was a discussion on this list some months ago about the effects of heat treating bamboo with comment by one member quoting his wife or friend (or both) who is a chemist suggesting that there is a chemical change within wood (presumably bamboo, too) upon heat treating that converts single bond to -OH groups to = double bonds, the byproduct being water. Whether this doublebonding occurs within the cell walls, within the cell centers, and/or within the lignin binders was not stated. From my crude understanding of cell structure, I would think that water within bamboo would exist between cells or within cells, not in the wall. Any water liberated from the wall structure would have to come from a chemical change. As far as low temp treating is concerned, I believe what others have stated. Even at 200F (below boiling), EVENTUALLY all "free water" will be liberated. Water is the smallest molecule in bamboo. It migrates between the larger molecules which make up bamboo's structure. It will just take a long time. The small permanent loss will be due to the "chemical conversion" process that can only occur if or when a critical temperature is reached necessary for that reaction. All of this is my opinion. I'm not a chemist, but an engineer. I have spent a good portion of the last ten years learning about and experimenting with organic coatings and solvents, so I am self-taught in chemistry. Sometimes that's dangerous!:) (Al Baldauski) Rick Crenshaw's post of March 10, 2001 is the one I remember even though I haven't been on the list that long! Someone else may have quoted him and I subsequently read it. Wayne, Rick's post, too, is hypothesis but based on discussions with his wife who is a chemical engineer working on the effects of heat on wood fibers for the past 23 years. (Al Baldauski) www! My ears are burning! Yeah, I don't know why I get into these discussions with anal retentive engineer types when I'm really a sensitive touchy-feely artsy kinda guy, but you are right. It were me. My good wife is a chemical engineer in the 'wood pulp bidness' down heah in Memphis. Now, if you just go and take a look at all them little letters that make up long cellulose fibers (them's the fibers that are in all woody plants and are nearbout identical in wood and bamboo) you'll see long chains of C's and H's, and O's and whatnot. Well, it seems that when you heat that cellulose up enough you can excite some of those letters like H and O and 'drive 'em' off where upon the leftover letters'll just take up a hankering for the nearest available letter what's got a strong need for some companionship. This creates what my wife calls 'crosslinking' and basically just ties those long fibers together a bit. What's more, once those crosslinking companionships take place, the old letter like 'H' and 'O' can't come back again neither! So now you have stiffer fibers due to their bundling together and on top of that, you have fibers that won't get as 'wet' as they used to. Course all this good stuff can be negated by over cooking and overexciting them letters to where the whole lot of them will begin to let go of each other and to the point that they's big gaps and breaks in the chains. Kinda burnt up like or overdried or sumpin'. Don't ask me what the ideal temperature is for doing the good stuff while avoiding the bad stuff that's done to the cellulose. I've asked my wife and she says we oughta just hire about a gazillion scientists and put 'em in a laboratory and everything like she and her company done for the pine and cotton fibers that they work with. I figure I like to just cook it awhile at 250 to drive off the free water, then hit it at about 325 to 375 for just a very few minutes to see if I can get that crosslinking bidness going on. That's good enough for Powell and good enough for me. I ain't got enough money to hire them engineers and my wife will want me to clear all the rusted cars out of our yard if I ask her to do it. So that's as far as I go with it. Uhhn-Hunh. (Rick Crenshaw) That is the best and clearest description I've ever heard of what is going on during heat treating. Of course I was born and raised in the Hills of West Virginia and understand that kind of talk... (Don Schneider) Crosslinking (caramelization) occurs in the mid to upper 300 degree F range, under common conditions about 350 - 360 degrees. It can be affected by the amount of water in the cane, among other things (such as ammonia). Destruction of the lignin that holds the fibers together occurs at a little higher temperature. If you get the cane too hot you can roll a strip between your fingers and be left with nothing but fibers and dark brown dust. I heat-treat at 375 degrees and watch the cane for color change; I can detect a "roasted" aroma at about the same time. In my system it takes nine minutes over a "flow" of 375 degree heat. (Bill Lamberson) Now if that don't beat all. Leave it to Rick to come up with clear, concise, pedantry to 'splain what goes on with our drying and heat treating. (Mark Wendt) When the bamboo is felled it contains a great deal of moisture. The bamboo will need some moisture content whatever its commercial use. Bamboo for internal use should have lower moisture contents. Bamboo like timber which is dried to quickly will degrade which is the name given to the lowering of quality which occur if uneven or too rapid drying is permitted. There looks to be a lot of confusion about moisture reduction. There really is two ways to look at it you can dry your bamboo by natural/air seasoning or kiln dry, with air seasoning its difficult in the UK to obtain a level less than 18 to 20% in natural conditions. This process is the oldest method of reducing moisture. It depends on the correct method of stacking to allow for the best results. there are disadvantages. 1 ITS DIFFICULT TO CONTROL THE RATE OF DRYING THE BAMBOO DRIES AT A SLOW RATE. Bamboo which is stacked correctly should be ready for use in approximately 7 to 8 months. The very large culms will be dry in approximately 1 year. The drying times are only approximately because of differences in weather conditions . KILN DRYING. When we apply heat to the bamboo this classed as kiln drying. It is capable of getting the moisture down to well below that of natural drying. I really think the most effective way to dry bamboo is by second seasoning first the bamboo is stored for a given time say 6 months then subject to heat drying then I allow further seasoning to place so the bamboo is allowed to reach the exact moisture level of its surroundings know as the equilibrium moisture content EMC. This method dries the timber without excessive heating. It also insures your measurements come out as first planed. If you apply to much heat you could incur case hardening of the culm. One other thing you cannot temper bamboo you only dry it. (Gary Nicholson) Aren't we talking about different things here? Bamboo needs to be dried, that's true. Air drying and kiln drying accomplish different degrees of the same thing. But your post states that bamboo cannot be tempered, only dried. Dr. Schott's work states that the breaking strength and bending to break strength CAN be improved with heat treating (pg. 16, pp.2). He believes bamboo can indeed be tempered. Are you disputing his findings? If so, on what basis? (Harry Boyd) First no I am not looking for a dispute of any kind. If we look at word temper to make harder (as in steel), I really don't think you can. Let me try to explain. Many years ago I used to produce rods in batches of 3 to 8 rods at a time. A lot of these rods were nodeless. They were all the same taper length and line weight. The only difference would be some would be dark flamed on the enamel some flamed on the inside. And yes some were made straight from the culm with no heat treatment at all. All the rods were produced in my garage at home. When the rods were finished they were kept inside the house until I got the orders finished. As a matter of fact I made that many I got a bit sick of making the bloody things. To keep sanity I used to try different things like subject them to different heat levels in the drying process, etc. One thing that really struck me was bamboo which was dried in the kitchen oven when made into a rod always produced a much more resilient rod. But and this is the thing. Some of the rods remained with me for some time, maybe up to a year or more. What I found was after some time, most of the rods, which I thought better for the tempering process, now did not show any difference in deflection or resilience to the ones which were well seasoned naturally for a given time. This said to me, "Yes, the cane is stiffer when it is drier." But when it reaches equilibrium there was no difference which I could detect. Remember, the rods were in a finished state with the guides on and at the time, several coats of varnish, all rods were stored in the same area of the room. I will say I am very skeptical of any study of heat treatments. I really believe believe you must allow the bamboo to come back to the point of equilibrium. I really cannot say if the tests done are wrong or correct. But you cannot judge tests in a lab with what happens in a workshop. There are simply too many variables involved. I would like you to think if that favorite rod of your's has lost its backbone due to overuse or is it down to moisture reentry. Varnish will not prevent this it only slows the process down. There must be more rodmakers that have experienced this. I would like to hear your side. (Gary Nicholson) I completely agree with you findings. I want to introduce you that Weather department of Japan Government is forecasting two interesting humidity statistics. One is actual humidity which a thermometer will show. The other is the humidity involved within some wood (I don't know which kind of wood they use). Both moves up and down in correlated manner but the latter moves as rather constant wave, like an average of actual. (Max Satoh) I see and understand your points. Though I rarely have the opportunity to keep several rods with the same tapers on hand to test your ideas, I sincerely appreciate your response. (Harry Boyd) This is an excerpt from a steam bending booklet published by Lee Valley. Of note are the comments on Lignin (them be the power fibers) "Wood cells are held together by a naturally occurring substance in the wood called lignin. Imagine the wood fibers to be a bundle of rods with the space between them filled with lignin. The strength of this lignin bond between the rods can be decreased by subjecting the wood to steam. With unpressurized steam at 212 Fahrenheit, steaming for one hour per inch of thickness (regardless of the width) will soften the bond enough for bending. Substantial oversteaming may cause the wood to wrinkle on the concave face as the bend progresses. Only air-dried wood of an appropriate species should be used. Kiln-dried wood must not be used; the lignin in the wood has been permanently set during the hot, dry kilning process. No amount of steaming or soaking will weaken the lignin bond sufficiently for successful bending. The same applies to air-dried wood that has been allowed to dry and stabilize below 10% moisture content; the lignin will only partially plasticize with steam, not enough for successful bending of anything beyond a shallow curve. (Leonard Baker)
I experimented with my usual procedure and tried Rick Robbins method of treating (275 degrees for 14 hours) and I must admit I liked the results. I actually treated the cane for 40 minutes at 375 then dropped the temp to 225 for 2 hours. The results were. Cane a little more golden and a much crisper response to flexing of said strips. I was planning the last piece of butt strip and about 2” from where the ferrule would have gone, a good chunk of the inside of the strip was torn out….I thought….the glue will fill….nah don’t be a putz, Trash it and do it right…so I broke the strip and it ripped apart beautifully with tons of splinters. It’s like the strands held together more strongly and resisted breaking much better than what they had in the past. Before when I bent the strip to break it and trash it, it was a much cleaner break than what I got last night. The splinters were a bout 1 ¾ - 2” long…. For what it’s worth….any feedback appreciated. (Ren Monllor) 375 for 40 minutes. . .conventional wisdom says you are terribly overcooking your cane! Garrison advocated 350 for 7-10 minutes. . .a formula that I follow fairly closely (shorter for tips, longer for butts). (Chris Obuchowski) I've been using M-D's heat treating protocol ever since I was one of the guinea pigs for his fixtures (and had my convection oven). Here's the way he had me do it, and I've been doing it since rod #1 - 360º for 30 minutes, then down to 225º and hold for an hour. This assumes that the strips are bound to the heat treating fixtures and the use of a convection oven. (Mark Wendt) I’ve got to admit, I was pretty afraid of over cooking my cane, but came to see that in fact, the cane remained very pliable while the individual strands of fibers resisted breaking. To my way of thinking, instead of becoming more brittle, allowing the cane to make a cleaner break under pressure, just the opposite occurred. My concern is, will the cane hold up under the same loads (fish fighting situation) as the cane that has been treated more conventionally. Bob Norwood stress test his rods, so I just asked him a couple of questions about those tests and am waiting for a reply. We’ll see. I don’t have a convection oven “YET”, nor do I use heat treating fixtures. What could the differences be in the end result to the cane aside from straighter strips, due to the fixtures and a bit more stable temperatures (convection oven)? What are your feelings between your finished product and others you have cast (things like taper and length being the same). (Ren Monllor) The fixtures were designed with the use of the convection oven in mind. Since the convection ovens have a much more consistent temperature (especially if they're PID controlled) throughout the oven, the fixtures help maintain an even heat to the entire length of the strip. If you get a chance to look closely at a strip bound in one of the fixtures, there are little doo-dads that run the entire length of the fixture where the cane strip is held, and this allows the heated air to circulate over most of the entire strip, giving a much more efficient and consistent heat treat to the strip. The old method of binding all six strips into a bundle is not quite as efficient nor as consistent in getting the heat equally the entire depth of the strip(s). You'll notice I added the plural in the parentheses. I can heat treat one individual strip if I need to, or any number of strips less than six if needed. The straighter strips are a side benefit of using the fixtures. That would be kind of hard to compare, due to the differences in heat treating regimens. I use mine more for consistency between all the rods I make, rather than somebody else's rods. If something starts to go haywire in my process, then I can nail down what I'm doing wrong if I'm not keeping all my steps from start to finish consistent. I know my/M-D's heat treat regimen works for the equipment I use, therefor I use it on all my rods and or sections. What works for me with my equipment, may or may not work with the setup somebody else is using, IE - non-convection oven, not using the heat treating fixtures and so on. (Mark Wendt) In all these discussions about heat treating, it seems to me the oven temp and length of time is always included, but the size of the strips are not. When I heat treat, the strips are .250". Wouldn't it make a difference if the strips were thicker or thinner? Mark, are your strips always the same size with your treatment? (Scott Grady) They are indeed. Unless the rod has a really big butt section, my strip size at the point where they are bound in the fixtures is as close to .220" as I can get them from the rough beveler. (Mark Wendt) One concern, though I have no empirical data to back this up, would be that you are weakening the lignins that bind the power fibers together, rather than weakening the power fibers directly, a change which would still lead to strip breakage. Again, nothing to back the idea up rather than the general admonition (and the slightly scientific data provided by Milward) against overcooking. (Chris Obuchowski) Never having attained the 'prescribed' 375 degree temperature in my electric oven, I've settled on a regimen which seems to accommodate the limitations. When the thermometer reads 300 degrees I place the 'strung up' sections in the oven, and that usually drops the temp. to about 290 degrees. The parts are left for 30 minutes, during which time there's an obvious ON/OFF cycle that raises and lowers the temperature some +/- degrees. After reversing the sections at 30 minutes, they're left for another 25 minutes. With the temperature gauge then reading about 280 degrees, the oven is shut off, and the the sections left to 'soak' as the oven returns to cold. One of my concerns is whether moisture in the oven has an adverse effect of reintroducing moisture into the bamboo. There is also the question of whether the smaller tip sections ought not be subjected to the same heat/time cycle as the butt section. It's my opinion that at the lower temps, the only effect might be the tips acquiring a bit more 'stiffness'(?) in the tips. Am I incorrect? Appreciate any/all words of wisdom. (Vince Brannick) My only concern would be that your may not be getting the actual "chemical/structural" change in the cane's structure at the temperatures you are getting in your oven. You are getting a "drying" of the cane, but without the chemical/cellular structural change, you really aren't heat treating the strips, you are basically just drying the strips, and as with any natural product like that, will absorb the water back into the cane that you've so carefully dried out of it. (Mark Wendt) Most of us (including myself) believe that, at a certain temp, the molecules in our bamboo fibers undergo a measure of crosslinking (polymerization). I think we all want this, but do any of us know for certain that it's actually happening? I'm not challenging anything here, but I wonder what evidence we have for our hopes, and at what temp does the process begin to take place? Does this crosslinking make our strips "stronger" (as we would tend to think), or does it just make the affected fibers resistant to moisture reentry -- or both? That is, is there a difference between "closing" the cells to moisture reentry, and actual, molecular crosslinking? And lastly, is it possible for temperatures lower than what's required for crosslinking to shrink and "condense" the fibers, such that moisture reentry on the cellular level is no longer a concern? It would seem so with the seasoning of true woods. (Of course, moisture will always come and go BETWEEN the fibrous material in our bamboo, but that's a matter beyond anyone's control. Only seeking to separate hopes from actual results.... (Bill Harms) The seasoning, or kiln drying of wood is not the same as heat treating it, since much lower temperatures are used to accomplish this. When you cut a tree down, it's basically still alive at that point with all the moisture and such in the "veins" to sustain it's life. That's excess moisture in the wood, and as the wood seasons or dries out, the wood tends to shrink, and if not done right, causes the wood to check and crack. It will eventually come into balance with the humidity in the air Vs the moisture in the wood, and stabilizes at a certain moisture content. When we heat treat at the elevated temperatures, and actually change the cell structure, that moisture that was driven out of the cell can't go back into it, keeping the moisture content of the cane lower than it would have been had it not been heat treated. With wood, the seasoning or kiln drying doesn't reach the temperatures where actual structural changes happen at the cell level. I'm not entirely sure if heat treating makes the strip "stronger.' What it does is make the strip stiffer, and less prone to take a set, and also keeps the moisture content of the strip lower than it would have been had it not been heat treated. I think Rick Crenshaw's wife had written up something a few years back on this subject. Rick, do you have that article handy, and if so, could you repost it? (Mark Wendt) I believe what you say about the effects of kiln-drying ordinary woods would also hold true for bamboo. Seasoned wood (kiln-dried or not) has moisture driven out of the cell structures, leaving the cells toughed and shrunken. So, just as with bamboo, the so-called "bound water" will not be able to reenter those cells. Kiln-drying indeed does provide cellular changes, although not similar to the molecular changes that we believe are involved with higher temperature, "crosslinking." (Reabsorbing "free water" around the cells is another issue, but no heat-treating can stop that process.) But your original post stated that: "You are getting a "drying" of the cane, but without the chemical/cellular structural change, you really aren't heat treating the strips, you are basically just drying the strips, and as with any natural product like that, will absorb the water back into the cane that you've so carefully dried out of it." This is the part that leaves me in doubt. Even though the elevated temps required for crosslinking may not have taken place, I don't think it's safe to assume that anything less will leave bamboo vulnerable to "reabsorb the water back into the cane that you've so carefully dried out of it." I believe this part of the process can (will) take place with almost any of our heat-treating regimens. (Bill Harms) It's all a matter of degree (pun intended =8^Þ). If the cross linking and cellular structural changes have taken place, it's physically impossible for the cane to absorb and hold as much moisture as prior to the heat treat. If a heat "dry", such as the typical kiln drying process were to take place, without the resultant cross link/cellular structural change taking place, it is possible for the cane to reabsorb as much moisture as was there prior to the heat dry. We do have to differentiate between green and seasoned wood/cane here though. My muddy sentences below were trying to convey that thought, though not very well. You do get cellular shrinkage as the material seasons/dies. Kiln drying hastens that process. But kiln drying doesn't reach the elevated temps necessary for the chemical changes. So, you won't go back to the moisture content of the green or unseasoned wood or cane, but you will go back to the moisture content of seasoned or kiln dried wood or cane. I'm still trying to dig up the numbers, but tucked somewhere back in the dusty recesses of my brain cavity I seem to recall the temperature was greater than 300º before those changes were effected. (Mark Wendt) A few years ago somebody on list mentioned using bamboo that was not heat treated in any way at all. I seem to remember it took a set but still cast OK. In any event the bamboo definitely alters. I goes from raw to cinders if you over do it and beyond a certain point it has to be non-reversible. That must change the nature of the material. Don't know re moisture reentry but the action changes from one state to the other. (Tony Young) I have visited with our biochemists about this process of driving off intracellular water. As I understand it, beginning at (as I recall) 340 degrees the lignins in the bamboo caramelize which is a process of changing chemical bonds in which there is greater double bonding between the carbons and creation of water molecules as a byproduct that are then driven off by the heat. That bonding is not reversible. So the loss of the intracellular water is really a creation of water through a chemical reaction, it isn't as though the water exists inside the cell and the heat causes it to evaporate. There is of course much free water being driven off in the drying process, and that is reversible. There are also some oils driven off at some point. I suppose the next question is whether heat treating is beneficial. I think so as long as it isn't too extreme. If the cane gets too hot for too long it is clearly damaging. The matrix between the fibers breaks down and I have had strips that I could rub between my fingers and be left with nothing but dust and power fibers. (Bill Lamberson) Thanks for the explanation. I knew the temp was higher than 300º for the process to take place, but couldn't for the life of me remember what it was. It kinda confirms Adam Vigil's experiments in heat treating times and temps. (Mark Wendt) Your predication that raises a question of the validity of there being a finite temperature at which a molecular structural change takes place in bamboo, surely merits consideration. Your question seems to ask that if such change occurs, How are we certain of at what point? In the case of metals, it may be assumed that x-rays may provide that information, but bamboo? Further, the question also may be asked whether Garrison (or Edwards), was attempting to predict such an occurrence, and the requisite temperature, or were they simply observing a change in the resistance to bending, and at the same time (in Garrison's case), recording the temperature at which some vaporization became evident ~ as well perhaps, of the time/temperature ratio when the bamboo became 'overcooked'? Water is known to boil (turn to steam), at 212 degree Fahrenheit. How soon after that does this (necessary?, desired?) structural change take place? We were once advised that placing strung-up bamboo sections in a long enough iron pipe, and applying sufficient heat from end to end, until steam is emitted, is all that's required. Is it possible that the rods built that way have all 'fallen by the wayside'? (Vince Brannick) It seems to me I recall one of our list members had a wife that was a materials engineer or chemist that provided us with this information at one time. Does anyone else recall who that was? (Timothy Troester) That would be Rick Crenshaw. Here's a link where you can find the information. (Todd Talsma) All my rods up to the early 90's were all heat treated in a black iron pipe suspended from the ceiling, heated with a torch, and rotated till the steam from the bamboo (and after a certain period of time) stopped. I am to this day still using these rods and they are in excellent condition and have not "fallen by the wayside". Only the building of an oven has changed my heat treating procedures, simplified the procedure and shortened the time required to properly heat treat the bamboo. If the iron pipe method wasn't so cumbersome I probably would still be heat treating by this method since it was very dependable. (Jack Follweiler) Thanks for the support Jacques ~ my old pipe is still up in the barn suspended from coat hangers ~ if you should happen to want to use it. (Vince Brannick) No thanks I have my own should I want to return to the old days. (Jack Follweiler) I still use it and would not go any other way (Ralph Moon) I'm sure your method of heating the cane in a pipe and detecting a change in odor of escaping gases when the moisture is gone has got to be the best that I've heard of. It tells you what is happening with each individual piece of cane instead of applying the same time and temperature to all. Unfortunately, twenty years of smoking destroyed my ability to smell much of anything. I'll have to stick to my 'second best' method. Hope to see you and Pat at the Idaho conclave. (Ed Berg) My pipe was of aluminum, lined with asbestos (dare I say it?) and worked if I was careful enough to not make charcoal. Which I did on a few tragic occasions. (Bill Fink) Your "tragic occasions" comment prompts me to share the following. Sometime ago, there was a 'thread' on the Fly Rod Forum describing some of the incidents along the way, of a number of beginning rodmakers. Although the author of the thread, my own account was never submitted. A history of sorts, however was prepared, with the intention to be contributed. There were numerous stumbling, bumbling episodes, with a first attempt, and one in particular is brought to mind with your 'confession'. Among the less predictable roadblocks was a serious health problem in the Spring of '79, which brought my first rodmaking adventure to a halt until the Fall of '81. At the time, teaching a mechanical design course at a Binghamton (NY) High school, I had access to a well equipped machine shop. The plan to build an electric oven was behind schedule, and being at a stage to heat-treat my bamboo sections, it seemed reasonable to utilize the heat-treat furnace in the shop in some way. During 'lunchtime' when the shop was devoid of students, the furnace was fired up, and the bamboo positioned above the vent hole in the top. While enjoying my lunch in the room across the hall, the air was suddenly permeated with ~ you guessed it ~ the odor emanating from Bamboo charcoal! Imagine my embarrassment. (Vince Brannick) How could that have possibly worked? No moving parts? No electronics? No sensors? No fans, strips, insulation? (Steve Weiss)
I have a poll on my blog that asks what temperature you heat treat at. Any discussion??? (David Bolin) While I voted, it is not only temperature but also time associated with the given temperature. As temperature range rises, time at temperature decreases and vice versa. Anyway, you should ask about time and temperature in my opinion. (Frank Paul) I totally agree. I just couldn't figure out how to put both in a poll without having a half dozen time periods for every temperature. Generally speaking, the higher the temperature the shorter the duration. And there are some folks that ramp up to a start temp, load the bamboo, turn the oven off and leave it until it cools down. There were just too many variables to include in a brief poll. As far as the poll goes, I decided the starting point was the temperature, not the duration. So I used temperature in the poll. We could do a followup poll on duration for what appears to be the most popular range from 326 to 375. (David Bolin) Agreed! I heat treat around 350, but only for the five seconds it takes to reach around and turn off the heat gun. The rest of the three hours the sticks are in, the oven is constantly cooling, 'til it reaches the ambient temperature. Then the cane comes out. (Steve Yasgur) I went to the page, and can't really vote in it. I don't heat treat over that large a range, I heat treat with a set temperature, plus or minus one degree at 360º for 30 minutes. (Mark Wendt) I put my bound strips in my convection oven for 2 hours at 180 degrees to draw out any moisture that might be in the strips (I don't soak my strips before straightening) and then bring the temperature up to 350 degrees with the strips still in the oven. It takes about 7-8 minutes to bring the oven up to 350 degrees. I then bake them for 17 minutes and remove them from the oven after the time has passed. (Don Green) 350 for 8 Minutes. (Richard Perry) Flamed + 320 for 15 minutes. (Doug Easton) I use a heat gun oven and preheat to 350 degrees F. (Nick Brett)
Someone asked me how thick are the butt strips and tip strips that I cook, and how much difference in heating time I use. I am an incorrigible user of the old "Shift/Delete" combination, so can't remember who it was. It was a question I couldn't answer off the top of the head, but have a set of bound rough planed strips downstairs ready for cooking, so I went and measured them. The butt section measures .580 at the fat end and .430 at the thin end. The tip measures .360 thick and .300 thin. These strips are destined to be a 7'0" 4 weight 2 piece rod. I will cook the butt for 10 minutes at 350 degrees, then add the tips and cook for another 20 minutes. My oven is not a marvel of pin point accuracy; it is built from a section of insulated ducting with the fan and temperature controls from a kitchen oven rescued from a fire-damaged house with baffles arranged to spread the heat fairly evenlt around the whole length of the oven and to eliminate any hot spot where the heat enters from the element. You blokes with your space age accurate microfurnaces would positively spew, but it works OK for me. (Peter McKean) After rough planing, I bind a strip to a piece of 3/8" x 3/8" hardwood, pith side out, and treat for my usual temperature and time ... 375 deg for 7 minutes. I let the single strip acclimatize to my shop atmosphere for a few days before final planing. (Ken Rongey) Huh. I tried that once with a 5 ft long, 5/8" square piece of maple that I routed a 60 degree groove in to nestle the strip. D**ned MAPLE came outta the oven like a corkscrew. Guess what shape the strip had, bound into the groove? THAT was when I saw the wisdom of the Darrell forms. (Art Port)
I use a simple heat gun oven and have always baked seven minutes on one end of the rough beveled cane and then turned it around and heated for seven minutes on the other end to kind of even things out. I only temper my finished strips; I throw them in loose. I use a simple oven probably like yours. For my one piece rods I put the butt ends in an aluminum cigar tube to protect them because they're closer to the heat gun. I don't turn them. I check them after 8 min at 325. Let them cool and glue them up. (Ken Paterson) Since you are heat-treating your finished strips prior to gluing, I guess this implies that the amount of heat treatment your strips receive is different from the tip of the strip to the butt of the strip. The very tip of the section receiving your full heat treatment regimen, while the butt (because of the taper) effectively receives very little, to none at all. This is very interesting...in other words, the *amount* of heat treating your strips are subjected to is variable, following the taper of the rod. It sure would be interesting to feel the difference in two rods with identical tapers, the first having rough strips heat-treated, and the other the finished strips heat-treated...hmmmmm???? :-) (Mike Biondo) What you are saying is true if the strips were not at the oven temperature, but I would think if they were in there long enough, they would all get the same treatment for the full length. (Dave Burley) The fact that my oven is basically a long pipe with a heat gun at one end means the end with the heat gun is hotter than the exit end so the larger butt ends get more heat than the tip ends so in fact the heat treating is actually fairly even. Butt sections I do for 12 min, mid sections 10min and tips I do for 8min all at 325 read at the exit end. (Ken Paterson)
I have a question about heat treating bamboo. I split and heat treated enough bamboo for 5 rods (about 2 years ago.) At that time, I did not have the M-D fixture, just rough planed the strips down to about .200 or had a good taper to them and heat treated at 200 degrees for 2 hours and 375 degrees for 5 minutes. Now a couple of excellant rod makers are telling me to heat at 375 degrees for 14 to 18 minutes. only.... My question is when did heat treating go to 375 degrees only. I do not want to create a stir or argument, just wondering what the rest of you guys do. (Lew Boyko) How many times while casting the rods at a gathering have you heard one maker turn to another and suggest that the rod needed 3 more minutes of heat treating or that the temperature was off 10 degrees? Maybe one of the gatherings should have several identical rods made with the only variable, other than bamboo, be heat treating. I doubt that I would notice a difference and would question anyone that said they did. You don’t hear a lot about the how the classic makers heat treated their rods. Paul Young had his ring of fire but I haven’t heard about other makers or their ovens. Chet Croco of Bellinger did say at SRG that they just flame treat their rods. In May, at Carolina Cane, I was discussing heat treating with John Zimny and he suggested a 4 to 5 hour treating at 230 to 250 degrees. For me that is a great solution since my oven doesn’t hold temperatures very well and I also flame my rods. I like the long time/lower temperature regime to heat treating. It reduces a lot of stress in my rod making by taking a Ron Popeil “Just set it and forget it” approach to heat treating. (Tim Wilhelm) I’ve been making rods for some time now and I have used Darryl Hayashida’s method of heat treating since I first came across it on this forum. I’ve never had a problem with it. (Ren Monllor) I think you will be OK and suggest that you test plane one to see how it behaves. If it's brittle put them away for a while until they plane decently. I cook mine at 380 or better for about 12 minutes or so and I believe that Schott's research indicated that the real changes don't start until a bit above your 350 degrees. A while ago I cooked some strips at my usual 380 and then thought I'd see what happened if I just let them cool down in the oven - bad idea. The next day they were dark brown and quite brittle when planed so I put them aside for about 9 months or so. I've just made a tip with them and they had regained enough pliability to at least be decently planable. So my advice would be to try to plane one and see how it behaves. If it's a bit brittle put them away for a few weeks and then try again. Keep trying until they work OK. (Cliff Parmer) Once again, this is probably a matter of personal opinion, and it may be that there is no "right" answer. My own feeling is that bamboo is not very expensive, nor hard to get, even here in far-off Australia - so why take a chance. I am not a rich man, nor one given to un-necessary levels of waste, but I am just NOT going to put all those hours of planing, gluing, fitting and finishing on what may well be dodgy cane right from the jump. Even in cases where I am encountering high levels of insect and borer damage in a culm, I will discard the culm or pass it on to someone who wants bamboo to practise planing technique. I sort of suspect that for every couple of borer tracts that I find in a section, there is going to be one I fail to see - just lurking there, a disaster waiting to happen, probably when the owner has a lifetime trout on, in tight water. Because I value the reputation of the rods I make and sell, I just cannot persuade myself that getting miserly over some questionable bamboo is worth it. Your "overcooked" cane may be fine, and if you only want to play with it and make a rod blank for yourself or your mother-in-law, fine. But if it were me, I would not be selling it, nor donating it to TU for a fundraiser, nor putting it into any forum in which I could be judged on its quality. (Peter McKean) I don't think there is an answer to your question. We seem to have a huge variety of regimens. Personally, I go from 10 to 20 min at 350* depending on the color I want. I also think (guess) that local humidity may have something to do with temp and times. I live in So. California where humidity is quite low. When I raise the temp to 375* the cane seems to be overcooked. (JW Healy) Something I did forget to mention; I do flame my bamboo culms to a chocolate color when I start this whole process... This last batch I did at 350 degrees for 15 to 18 minutes. When I opened the oven door, there was this wonderful odor, smell of bamboo, nothing burned, just a wonderfull smell of bamboo from the oven.... I will go with that... (Lew Boyko) The 375° F seems to mostly come from Bob Milward. It is a figure based on his testing and some former work done by Wolfram Schott (“Bamboo in the Laboratory”) and is not only in the second edition of Milward’s book, but he has also recently written about it in “The Planing Form.” Should all of us now follow that? Well, JW has already pointed out that the topic is not a new one! Most seem to agree that heat treating drives off water, not a great intellectual leap since it might well be compared with kiln drying. What color changes mean and how best to achieve them is where most disagreement seems to occur. I suspect that what you have already done is quite sufficient. Another Tim just wrote, "I like the long time/lower temperature regime to heat treating” and I agree with him (maybe that’s because it is what I do). I like doing that because I know that the interior of the cane has reached the oven temperature. (Tim Anderson) I'll add my two cents worth on heat treating. I use this oven with a PID controller which stabilizes the temperature of the oven wall. When I heat treat, I insert a thermocouple into bundle of bamboo to monitor its actual temperature. What I have found is that its temperature lags the oven temperature for quite a while, until the moisture is all boiled off. So what I do now is run the oven at 250--275 F (above the boiling point of water but well below heat treating temperature) until the temperature of the bamboo stabilizes there as indicated by the thermocouple. This can take an hour or two. At this point the moisture is mostly gone. Then I raise the oven set point to 350. The bamboo temperature follows it up without much delay. I have been doing half an hour at that temperature. My overall point is that the effective time at heat treating temperature can be confounded by the amount of moisture in the bamboo at the start unless care is taken to manage this. (Mike McGuire) Just to set the record straight, Bob Milward's most recommended temperature for heat treating is 392 deg F (200 deg C), not 375. He advises that once the cane begins a color shift, treatment should be stopped. Amber is too dark. This could occur in as little as 8 minutes and tests should be done prior to heating good cane. Slower treatments at lower temps are also good, but only if halted once a slight color change has been detected. The hotter/faster method is better, according to his tests, but obviously harder to control. All flaming or torching is very bad and weakens the bamboo significantly over time. His tests and methodology are gone into at great length in both the first and second editions of his book, Bamboo: Fact, Fiction and Flyrods, although there are updates and revisions on just this subject in the second. Again, these are Milward's conclusions based upon what seem to me vigorously controlled testing. Whether you subscribe to these ideas or not, it is very interesting, illuminating reading. Highly recommended. (Bob Brockett)
I have reviewed books and forums and there are a wide range of temperatures/times suggested for heat treatment of strips. I flame the enamel for color and what like to narrow down an approach (i.e., temperature/time) for heat treatment via a heat gun based oven. (Ron Delesky) I was taught to heat treat at 350-375F for 20 minutes, swapping end for end after 10. I also flame many of my rods. Several of us flamed a culm and read the temps with an IR thermometer which averaged about 250F which is not hot enough to accomplish what heat treating needs to accomplish. Consequently, even though I flame, I still heat treat with the same regimen. Just my .02, open to change. (Marv Loopstra) You will get as many responses as there are rodmakers!I heat treat with a heat-gun oven, bringing the oven up to temperature and then inserting the cane. I use the aluminum jigs sold by Harry Boyd. Using two thermometer probes, one in the flow of air and the other up against the cane, I bring the CANE up to my desired temperature, turn it around, and bring it up to temperature again. The whole process takes over an hour. I heat set the epoxy I use to glue up the blank at the same temperature I heat treat at. I don’t give my temperature because I think you can select anything which gives you a result you like. (Tim Anderson) I am using a standup hot air oven. Depending on the desired action and memory effect of the bamboo, i put the strips in the oven for 20 to 40 minutes at 170 oC or 338 oF! Swapping them at half time. (Torsten Wieczorek) I have been making and teaching rod making for over 21 years. I have always followed Wayne's method which is... 375 for 7 minutes (switch half way of course) (Doug Hall) For the guys that treat at 350 for a half hour or better. What color are the strips when done. I just baked a rod at 350 for a little less than 30 minutes. Mine came out a light brown or dark tan would be the best discription of how they looked. A definite color change. Just curious (Rick Barbato) 365F for 18 minutes in a convection oven. Reduced to 15 if flamed providing the cane is flamed and given 4 days to rest for moisture reabsorption. (Don Anderson) My current heat treating regimen with a heat strip type oven is to bring my bamboo strips that I have bound to Boyd heat treating fixtures up to 275° and monitor the amount of steam coming off the strips (open door, place face with glasses on near opening, note steam fogging up glasses and note the smell as well. Aka: Glenn Brackett monitoring style...). This has taken anywhere from 50 minutes to an hour and a half, depending on the bamboo moisture content and the quantity I shove into the oven...
Now, all this may change over time, but this is my CURRENT regimen.... (Don Smith)
Over the last few days a handful of time and temperature regimens have been generously shared on this list. A common theme seems to have emerged. Through heat treating we seek to introduce a change in both moisture content and/or makeup in the bamboo, as well as a color change of some sort. I did not save each email detailing a time/temp regimen but they seem to range from 250-375 degrees Farenheit over a time range from a few minutes to a couple of hours. I'm sure all of these work for the various practitioners. Here's what puzzles me... I remember discussing this many years ago on this List, sometimes passionately. Proponents of the high temperature / short time methods would argue that longer times might well scorch the bamboo or at least scorch the side nearest heat sources, and also argue that high temperatures were absolutely necessary to initiate the chemical changes in bamboo we seek in heat treating. Low temperature / long time proponents would argue just the opposite. A few folks would propose that the very best bamboo required little if any heat treating at all, though admitting that supplies of super-high quality bamboo were rare. Through the findings of Dr. Wolframm Schott and Bob Milward and possibly Ralph Moon, a majority of folks seem to have settled on this idea of a slight color change, and a change from steam to smoke exiting the ovens. What I don't understand is why some of us with our various ovens and measuring schemes seem to have settled on times and temperatures that would not achieve the desired results with different ovens and measuring schemes. I'll use my friend Doug as an example -- he follows Wayne Cattanach's recommendation for 375*F for seven minutes. In my oven, that does nothing. But it works for Wayne and Doug. Why? Someone else suggested waiting till the bamboo reached a certain temperature then holding that for half an hour or longer. In some setups, that produces ashes. Why? What are the differences that cause us to settle on different regimens? Why does 375* for 30 minutes burn bamboo in one oven, but produce desired otucomes in another? Ideas? (Harry Boyd) One potential difference is the type of oven. A heat gun oven is effectively a convection oven. I've compared the actual in the oven in my kitchen on normal bake, and convection bake settings. The oven had the convection bake setting so you can follow the directions in a recipe and bake for the same time as in a standard oven. If I set it 350 degrees on convection bake, the actual temperature it uses is 300 degrees. So just the movement of air in the oven raises the effective temperature by about 50 degrees by disrupting the boundary layer around the food. That means that 325 in a heat gun oven should be about the same as 375 in a strip oven. (Robert Kope) Say what? If your oven loses 50 degrees when you turn the convection on, I certainly wouldn't consider that a reliable heat treating oven. I use a convection oven that I designed, built and posted drawings for on the list many moons ago. It uses a PID controller to manage the heat. I can say without a doubt that when I set the PID controller to 360 deg F (which is my set temp for heat treating, held for 30 minutes), that every inch of the chamber that holds the bamboo is within 1-degree F of that set temperature. That's what a convection oven is supposed to do - maintain a constant temp throughout the entire heat treating chamber. The movement of air does not raise the effective temperature. Temperature is temperature. If you need a certain temperature to effect a chemical change, hitting 50 degrees below that temperature even with air moving is not going to effect that chemical change. Your oven has either got a very poor convection setup where the air flows poorly, or a bad heat control or thermostat. (Mark Wendt) I made Mark's convection oven about 10 years ago from the plans he was kind enough to post. I used a Watlow PID controller. The oven stays within 1* front to back no matter what the ambient temp is in my shop area, anywhere from 50* in the winter to 90* in the summer. Because I use Harry's heat treating fixtures I set my initial temp to 395* to allow for the rapid temperature drop then I throw the sticks in and reset temp at 365* for 15 to 17 minutes. (Tom Vagell) If you're using the fixtures, you can put them in the oven while it's cold, and let the oven bring them up to temp. No need to put the strips in cold after the oven comes up to the set temp. That's the beauty of using a convection oven. No hot spots to worry about, and it heats evenly. (Mark Wendt) Possibly because there is no specific standard as to how a piece of bamboo should end up being. Add to that, all of the different variances as to differences in equipment and equipment components, climate, humidity, humidity content of each piece of bamboo, personal preferences, personal interpretations (what is the color of "that" banana). Everything effects everything. If there are any differences in any one thing, it will create a different set of outcomes.In your example high temp/short time period vs. low temp/long time period, at some point, it evens out as internal temp reaches same amount of degrees to create more or less the same reaction or desired effect. Or possibly the laws of Physics are just different in my home ;>)... Be well, (Ren Monllor) Poor thermometers? I'm still in the dark ages with a mica-strip oven. I have two thermometers in it, towards either end. When I put them in they were 25-50 degrees apart (I forget exactly) so I switched the thermometers end-for end, then I got the same reading. So, I switch the bamboo end-to-end halfway through the treating regime knowing it is getting to at least 350. Seems to work, and avoids the problems of building a new oven or getting better thermometers. (Henry Mitchell) I have a mica-strip 61-inch-long oven that was built on the Wayne Cattanach design. I have not used it a lot as I am a relatively new maker, but I became concerned with it's ability to comprehensively heat treat my bamboo strips. Communication with other members of our community suggested that these types of ovens are notorious for hot and cool spots within the heated cavity, so I decided to test the temperature at 5 locations evenly spaced along its length. I drilled 5 holes down through the top to accept the probe of 5 each 9847N Taylor® Pro Waterproof Instant Read Thermometers. I spaced them front to back at 6", 15", 29", 43-1/2" and 55" positions. I do not obtain a target temperature on the end thermometers. They lagged behind the center 3 thermometers 30°-50° or more. I decided to not be too concerned about these end temperatures in large part due to the fact that the bamboo strips being heat treated were over length at least 3" on either end anyway for the 'working' length, which, of course, is longer than the 'finished' length. So the actual effective heat treatment would take place on the central area of the cane. Regardless of what type of oven setup you use, I think it is important to insure you know how accurate your entire oven cavity is heated, and apply whatever thermometer reading device(s) you need to obtain that information. So, what conclusions I made with my oven is:
At the end of the first timing sequence, I remove the strips and swap end-for-end and back into the oven they go. Since there is a temperature drop during this operation, I again wait for the center thermometer to reach my target heat treating temperature, then start the final timing sequence. NOTE: You can remove the thermometers during insertion/removal of bamboo to preclude catching on the probes. Just reinsert them after you close the door.
So far, this regimen has been working for me but may be modified at any time. Sorry it seems so wordy, but that's just the way it is... (Don Smith) There is an assumption being made in every post I have seen in this thread--that the temperature of the bamboo is the always the same as the temperature of the oven. By monitoring the temperature of the bamboo with a thermocouple in direct contact with the bundle of bamboo, I have found this is not so. When I place bamboo in a PID controlled oven running at a set temperature, the oven temperature dips and then recovers to its set point. The temperature of the bamboo lags that temperature for a long time after that. Why? Some very basic physics: between 0 C and 100 C it only takes 1 calorie to raise the temperature of one cubic centimeter of water 1 degree. To go from 100 C to 101 C it takes 540 calories--that's what is takes to vaporize that water. The bamboo temperature if being limited by the evaporation of water form it. Given the variable amount of water in a batch of bamboo, a simple time/temperature process is going to give variable results. So how to overcome this? Monitor the temperature of the bamboo. I set the oven temperature to around 275 F / 135 C, well above the boiling point of water but well below the 350 F / 175 C that is considered to be the effective heat treating temperature. The bamboo takes whatever time it needs to reach this temperature. I don't figure I need to worry about how long it has been at this temperature when I get around to checking it. Then I give it another half hour or so to be sure. At this point the water is pretty well cooked out of it. Then I raise the oven temperature to 350 F/ 175 C and find the at bamboo temperature follows it with little lag. I give it 20 minutes at temperature and then I am done. To demystify thermocouples--a thermocouple is formed the junction of two dissimilar metals. The preferred type for this application is type K, chromel-alumel. The junction produces a small voltage with varies with temperature. The junctions are made ideally by welding the wires together to make a small bead. Twisting them together and hitting the twist with a hammer to cold weld it also works. The wire is sold as a pair; McMaster-Carr is a source. I recommend size 24 solid wire, about $1/ft. On the other end a connector for type K is needed, also available from McMaster. To read the temperature a instrument is need. Harbor Freight sells a digital multimeter with a type K input--about $24. It only reads in degrees C. Another one I like is available from Amazon. (Mike McGuire) When I heat treated with rough beveled strips, I used MD's (now Harry's) fixtures, and put them in the oven while the oven was cold. Then I turned the oven on and the bamboo/fixture combo came up to temp with the oven. Granted, the strip temp probably lagged the oven temp a bit, but I use 360 as my set temp, and hold that temp for 30 minutes once the temp stabilizes on the PID controller. Realize of course, this type of heat treating regimen should only be done in some kind of convection oven. (Mark Wendt) I also built one of Mark's designed oven, with a few changes. I follow his heat treat methodology too and since I switched to thisoven a couple of years ago, I have been more than pleased! And I thank you again Mark for all of your help. (Scott Grady) Glad it helped. I got my design originally from MD, and made a few changes. Robert Holder took my design and went a little further with changes, using a very neat system for mounting the motor and fan. I made a few more ovens for friends, and incorporated that change in those builds. I've got a roundtuit laying around somewhere to make the change on my oven too. (Mark Wendt) In addition to the variation due to different ovens and temp measuring methods, there seems to be a lot of difference in the size of strips people are treating. (Frank Stetzer, Hexrod, Taper Archive, Rodmakers Archive) I have a question... During the process of polymerizing the cane... Does the cane act like water boiling... By volume (mass) when enough heat is applied... In other words, does the entire stick poly when it reaches the proper temp (360 deg)? Therefore, the time to get it to temp is the critical factor and not the duration at that temp? Do we know at what temp the cell walls burst? It seems as if the temp of the cane may be the critical factor and now just the temp of the oven. If the cane transitions at a given temperatuire then what does the extra time gain? (Jerry Foster) Just precisely what do you mean by "polymerising the cane"? It does not say anything specific to me at all. In fact, I am inclined to regard this whole heat-treating mish mash as something of a mare's nest; and no figures I have ever seen have been based on anything like a sufficient number of observations as to be statistically very significant. (Peter McKean) I was referring to the process of supposedly " cross linking the starches and lignin's " in the cane (tempering). I don't know if anyone has used SEL on tempered cane to prove or disprove this theory. Heating the cane to drive out water only seems like a silly thing to do as it will become quiescent with the relative humidity and a few days anyway. Good question for all to ponder, thanks. (Jerry Foster) I asked the original question in hopes of starting just this sort of discussion. Why do various time/temp regimens seem to work? I’ve been reading all the posts to this thread over the past several days with a mixture of amusement and amazement. Amusement because so much junk and mis-information has been passed out. Amazement because I can’t believe how many people have apparently failed to take the time to do a wee bit of reading and research. Bob Milward has addressed all the essential elements of the topic that have been discussed. He has done his homework by investigating the available literature on the subject (limited as it is). He has consulted with the most knowledgeable people he could find. He has run objective experiments and collected quantitative data. And, most importantly, he has published it all for our benefit. Bob wasn’t able to answer all the questions as completely as I’m sure he would have liked (the details of the chemical changes that occur in the bamboo during the heat treating process are still not well understood, for example) but he was able to develop useful guidelines that can be used by anyone to develop a heat treating procedure that will give them near optimal results under their own unique conditions and in their own personal environment. So why haven’t you all read Bob’s book? There really is a whole lot of very good information in it. I suggest that everyone take some time to do a wee bit of studying, then we could start a productive and informative thread by discussing Bob’s experiments, his results, and what sort of experiments/investigations could or should be done next. That’s a discussion I would really enjoy participating in. Just my 2 cents. (Bryan Coles) My apologies if this has already been posted in this thread. Here are a couple of links to heat treating research that may be helpful (Bamboo in the Laboratory) (Bob Milward Information). I have been reading these posts on the bamboo ovens we use for making rods. As most if not all of you know I have been making my mica strip oven going on almost 20 years. I started making these based on Wayne Cattanachs oven with his approval because there was nothing out there commercially & I was asked by Nobler to make him one. It took off from there. For several years my oven was the only one out there until Harry Boyd starting making his heat-gun oven. This addition was needed because some do not like the oven I make. So now we have the two options commercially. Both work well & you will get varying opinions as to how well. Mine has given many rod makers good results & they will stick with that though it was recently referred to I believe the dark ages of ovens where the heat gun oven has been referred to in the past as the flaming bazooka of death. You can form your own opinion on what you like. There have been many different types of ovens put to use by rod makers through the ages. Garrison had his black pipe wrapped in asbestos insulation that he had a gas burner underneath, Leonard used a wooden box with light bulbs in it that they put there strips in for I believe several days. There have been charcoal grill looking ovens, horizontal ovens, the Circle of Fire by Paul Young & I am sure several other types that have been used. Mark Wendt has his convection oven. Some guys even believe you don't need to heat treat @ all & that it ruins the cane. Then we have the different times & temperatures that everyone is so worried about. Is it 365 or 375 for 10 minutes flipping half way through? Or was that 250 for 24 hours? So now we have this issue the time & temp vs the style. Guys I think the best thing to do is find out what you want or like in an oven. Make it or buy what is out there, learn what it can do & experiment a little with your oven. Heat treating the cane will have many variables. Do you soak your strips, what is the weather like where you live, what time of year is it, is it raining, is it humid today & on & on? I have 375 for 10 minutes for flamed rods flipping half way through, 375 for blonde rods as above & then an additional 5 minutes on 325. That was what Wayne suggested. I do this but I also keep an eye on the steam being released from the oven. I also preheat my oven for 20 minutes before a stick the strips in. This was figured by trial & error. I am in Arizona but when I was in Michigan this also varied. So for a recap here learn to use what you have & figure out what works best for you. Good luck & have fun making rods & quit stressing over heat treating I am sure that everyone's rods are turning out just fine & cast well. Well off to build an oven got another out going out this week. (Bret Reiter) Being an empirical type of guy and builder I know what I like. I have been flaming my bamboo since I started building 15 years ago. The reasons were I didn't have a oven and I like the way flamed cane looks. I have had no problems and don't see the need for a oven. I think we are putting way too much credence on heat treating. I might be wrong but so far my rods don't tell me that. (Mark Heskett) Whimsical temperature control perhaps, Harry? (Peter McKean) Perhaps, Peter. Or even shop gremlins; or fairy dust. (Harry Boyd) I would think that all the variations are in a large part to ovens that have cold/hot spots. Probably the worst "tool" is Garrisons book is the oven and of course it was replicated by Cattanach and on and on. After trying a number of oven types, I went with a convection oven many years ago. The reason, I just couldn't get replication without some type of convection oven. MD used my drawings and info to create his that was passed along to others. They all share the same feature, decent air flow allows for homogenization of the air and no cold spots. Addition of extra mass through the use of your "fixtures" certainly will increase time to recover to proper temp. Also, some builders do not rough plane and then temper but final plane and then temper. Lots of ways to do things and they mostly work out. (Don Anderson) What Don said. MD's and my ovens are direct descendants of Don's oven. Thanks for doing the leg work Don! Convection is definitely the way to go if you want over-all even heat. (Mark Wendt)
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