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Heat Treating - Regimens


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Rule

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)

Rule

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)

Rule

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.

  • 5 minutes @ 350 setting R=125  M=118  F=122
  • 10 minutes @ 350  R=180  M=190  F=183
  • 15 minutes @ 350  R=230  M=260  F=233
  • 20 minutes @ 350  R=250  M=296  F=257
  • 25 minutes @ 350  R=265  M=341  F=257
  • 27 minutes @ 350  R=310  M=350  F=312
  • 30 minutes @ 350  R=285  M=350  F=312

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.

    • 0 minutes (entry)  375
    • 1 minutes 355+
    • 2 minutes 345 (thermostat on) (and note the temp dropped 30 degrees)
    • 3 minutes 340  (note the thermostat is on but the temp is still dropping)
    • 4 minutes 335
    • 5 minutes 340
    • 6 minutes 345
    • 7 minutes 350 (thermostat off)
    • 8 minutes 355 (and here the thermostat is off but the temp is still rising)
    • 9 minutes 360 (turn strips)(here is where you need to watch for temps creeping up and getting dangerously high after you turned the thermostat off)
    • 10 minutes 355
    • 11 minutes 355
    • 12 minutes 350+
    • 13 minutes 350
    • 14 minutes 345 (turning the thermostat on here would be optional, in this instance I didn't)
    • 15 minutes 340+
    • 16 minutes 340
    • 17 minutes 335
    • 18 minutes 335

    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)

Rule

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;
    325,15; 320,20; 250,30; 350,20; 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;
    mutemp = 347; mutime = 13; J = 2170; S = 13640; r2 = 0.8409

    Model 11:

    temp(degf) = -4.9 * time(minutes) + 414;   (This is the one I sent yesterday.)
    mutemp = 347.3; mutime = 13.6; J = 3555; S = 12263; r2 =
    0.7101

    Model 12:

    temp(degf) = -4.96 * time(minutes) + 416.5;
    mutemp = 349.6; mutime = 13.5; J = 3909; S = 12613; r2 =
    0.6901

    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)

Rule

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
Sent: Wednesday, February 22, 2006 2:57 PM
To: Jim Bureau

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
                                                                                 (oz/in2)      (psi)

#1   230 degrees F @ 2 hours    3.67 x 106       921,113     57,570
#2   300 degrees F @ 30 min.    4.72 x 106      995,494      62,218
#3   325 degrees F @ 20 min.    4.66 x 106     1,044,948    65,309
#4   350 degrees F @ 10 min.    4.66 x 106     1,022,030    63,877

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)

Rule

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)

Rule

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)

Rule

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)

Rule

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)

Rule

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)

              ll 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)

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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)

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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)

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