I must say that, having tried several methods of producing straight sections, I am quite convinced that there is none so simple, nor so effective, as simply binding carefully and then taking a bit of time to tweak and straighten prior to hanging to dry.

There are several charms attendant on epoxies as a class, one of which is their very long working time. There is just no hurry, and it is an easy thing to take the time and get the section right. If the string subsequently comes off to reveal some minor bends that were not visible under the string, then good old epoxy will allow easy heat straightening with no appreciable price to pay for this.

It is worth noting that the time required, and the amount of heating necessary to achieve plasticity is very, very small, (seconds on tip sections) and I suspect that most of the horror stories about heat-straightening destroying sections may be stories here the process involved much, much more heat than is really necessary.

But, and this point is also worth making. I think that these days I probably spend more time on initial strip preparation than I do on final planing. I like to start the establishment of the initial 60 degree angles using strips which are already as physically straight as I can make them, with all four facets straight, square and true, and the nodal humps pretty well gone.

"As ye sow, so shall ye reap" somebody once commented. (Peter McKean)

I believe you're essentially correct about the ease of straightening Epon-glued strips. This is because the "curing" regimen in one's oven (say, three hours at 180 degrees the day after the glue has set up) does not entirely cure the glue. It's damn tough at that point, but there remains a period of perhaps at least another day or two when the strips can easily be straightened. Within a week, however, the glue will have reached its full strength and straightening at that point is nearly impossible, requiring more heat than the cane can really bear.

I wonder what others have found in this regard. (Bill Harms)

Well, galvanized by Bill's remark about the permanent setting of the Epon in a week or so, I just had a go at those two tips with a steam iron. One is a straight as it ever will be, and quite good. The other will have a slight sweep forever and various attempts to get it straight and the elapse of time has set that Epon hard I am sure.

Thanks gentlemen all for your useful remarks throughout.

I am also noting carefully Peter's remarks about strip preparation to essentially remove or minimize the need for straightening. (Sean McSharry)

I use Epon too, and have found that even after I heat cure the blanks, with judicious application of heat you can still straighten rather easily, whether it's right after the heat cure, or even a week later. (Mark Wendt)

I find it amazing that many of us follow procedures that are very similar, but our results are often nothing alike. Several years ago we pursued a thread on heat treating that comes to mind. Some said 7 minutes at 375 was just right. Some said that same recipe did little or nothing. Still others said the same time and temperature produced charcoal.

I have two sets of 3/2 rod blanks glued with Epon and heat set more than a year ago in the shop. They have the normal crooks and kinks. I'd almost bet you that working just like normal I can have both blanks straight as arrows in an hour. Yet I hear my friend Bill say that he finds straightening Epon glued blanks nearly impossible after a week or so. It intrigues me. Not long ago someone else on the list implied that Epon glued blanks were especially tough to straighten once truly set.

I have always believed that in straightening one softens the bamboo rather than the glue. Am I wrong about that? (Harry Boyd)

I suspect that with Epon, both the glue and the bamboo soften, although to differing degrees. I agree that sections can be straightened with heat no matter how much time has passed. (Steve Weiss)

I was the guy who had a bad experience with straightening epoxy-bonded sections after heat curing. I agree with Bill that once heat-cured, epoxy bonded rods can't be straightened easily if at all. However, I don't agree with Bill when he says 3 hours at 180F doesn't fully cure. My information from the manufacturer suggest that in fact this regimen does fully cure the epoxy.

As far as the straightening process goes, my IMPRESSION is that heating to straighten a blank softens the glue enough so that the splines can slip a microscopic amount. That is, the glue is plastic. I haven't done a careful experiment to back this up but I think that the temperature necessary to cause the DRY bamboo to become plastic would be too high for most glues. (Al Baldauski)

I hope you'll give the crooked sections you mentioned a try. I'd really like to hear what the results are. Despite the risk of blowing holes through my theory, I hope it works great for you.

But, here's "wrinkle" concerning Epon that I've often wondered about. The factory spec. sheet explains that a range of mixes (resin-to-hardener) will produce widely varying physical properties. The recommended mix is 1:1, but one can safely go as far as 2:1 (resin-to-hardener). The primary differences from one to another are the strength of the cured bond and the time needed for full cure -- the less hardener, the  longer  the  cure-time and  the  greater  the  bond-strength.  (I always use a mix of 1.5-to-1, thinned a tad with lacquer thinner) But what I'm wondering is if there are also changes in how the various mixes react to heat.

Because we're working with a laminate and several, radial glue lines, I always thought the glue would need to become somewhat pliable right along with the cane -- thus allowing the straightening to become permanent, once cooled. I think it's a mistake to assume, with a laminate in particular, that whatever the glue is, it will be happy to just sort of "go with the flow" when the rod section is heat-straightened. On the contrary, I think if the glue can become pliable while heating the cane, the straightening will work, but if the glue has more resilient physical properties and cannot soften enough to accommodate some stretching, permanent straightening won't happen.

There are, of course, forces of compression and tension in the straightening process which heated cane can easily accommodate, but if the glue cannot not do likewise, apparently the new shape of the cane can't overcome the resisting glue lines that want to go back to "business as usual." (That said, it may be that a butt section, with it's greater mass, could be a different case than a tip section.)

All glue becomes plastic with heat, until a certain point is reached when the glue begins to fail and break down. But the big question is: what ARE those temps? I think we've all found that various glues react quite differently. When straightening a section, there's a sort of "window of opportunity" as far as heat is concerned, where both cane and glue become softened enough to allow the bending. One hopes the glue is such that it merely becomes pliable, stretches along with the bend, and upon cooling, returns to its original strength.

Most glues will do this, although some (like Elmers and Titebond) have a narrower window and risk loosing their bond rather early in the heating process. Unfortunately, others, like fully cured Epon do not become pliable until the cane is all but scorched -- maybe not even then, I'm not sure. I've had excellent results, however, straightening rod sections even on the second day after the oven "curing" regimen. But after a week or so -- Whooo-ee, you got trouble. (Bill Harms)

Methinks I'd try less heat for a longer time if I was having trouble straightening a rod. (Neil Savage)

I will give those crooked sections a try tonight.  As I mentioned before, I suspect I can bend them into pretzel shapes without harming the bond or scorching the strips. One thing that makes me think I can is that the only two rods I made which have "taken sets" were no trouble at all to return to straight. As far as I know, they are still fairly straight. Of course, this is only anecdotal evidence.

Mentioning the different resin catalyst mixtures started me thinking. I actually don't use the 828 resin and 3140 hardener that many others do. Martin Darrell Odom and I talked  at  length  with  the  technical  gurus  at Miller-Stephenson and Shell. They strongly suggested using 826 resin because it is thinner (don't remember if "thinner" is more or less viscous). They also suggested a combination of 3140 and 3126 hardeners. I currently use the recommended combo of resins, mixed at 79/21 by weight. I premixed a pint of the hardeners, and use a 50/50 mixture of 826 resin and the combined hardeners, by volume. Perhaps my use of the different resin and hardener accounts for my ability to straighten at will, although when the tech guys were asked about the differences in strengths and other properties between the mixture I use and the semi-standard 828/3140 mixture, they acted as though the differences were very slight. Why change from the established mixture? Well, to get a thinner mixture and ostensibly smaller glue voids, and to get a higher heat deflection temperature (whatever that means). The different resin/catalyst mixes also allow me to safely mix small quantities of an ounce or less by volume rather than dragging out the gram scale each time I glue something.

There is definitely a difference in the way the 2/1, 1.5/1, and 1/1 mixtures react to heat. You may be on to something here.

Another interesting point of debate concerns the practice of heat-setting at all. The tech guys told me that cured is cured, no matter how we get there. You can cure at 350 degrees for 7 minutes, or 180 degrees for three hours, or a week or two at room temperature. According to the tech folks, there is no difference.  Like you, I cure at 185 degrees for 3-4 hours. Why? Well, that's how I was taught to do it. Reminds me of an old story about a wife, a roasting pan, and a ham. You know the one.

I remember hearing or reading somewhere that there is a window between 140 degrees F and 190 degrees F in which we can work with completely cured glue... but I don't remember exactly what those temp's represent. A little common sense tells me that those temperatures are very warm to the touch, but not quite hot enough to scald skin. So when I get the cane so warm that I can just barely hold it, I'm in the right temperature range.

One neat thing about Epon is that even completely cured Epon remains quite flexible. Next time you glue some strips, pour the excess glue on a pane of glass or plastic. Let it completely cure. Maybe even heat set it. Using a razor blade you can scrape the whole mess off the glass. It will still be quite flexible. You can stretch it, bend it, even try to crease it. It cuts like butter with a sharp knife. In fact, it seems quite rubbery.

Someone mentioned humidity - temperature - skill variants. Skill might make some difference, but there is no question that both Bill and Harry have built enough rods to be at least proficient at it. Degrees Fahrenheit is degrees Fahrenheit, whether in Louisiana or Pennsylvania. As I understand it, humidity should have absolutely no effect. Epoxy will actually cure underwater if the temperatures are suitable.

I'm afraid the mystery remains. Why do rod makers A and B have different results with quite similar, almost identical, practices? Perhaps that's part of what keeps this craft interesting. Tell you what, my friend, if I can straighten those section in the shop tonight, I'll set up a straightening service as part of Boyd Rod Company, Inc. Then I can straighten all your tough kinks and bends for you -- for a small fee, of course <g>. (Harry Boyd)

Resolution Products now produces the Epon/Epikure line of epoxies. According to their literature this is what happens when you mix at different ratios and cure at different temperatures:

          A        B      C      D

Epon 828    100 pts   100pts   100pts 100pts 
  These are parts by weight (100/45 equals 2:1
  by volume)

Epikure 3140 45 pts    90 pts   45 pts  90 pts

Ultimate flexural strength

          14000    12000   12500  11000

Ultimate tensile strength      

          8500     7300    7400   7500

Heat Deflection Temp (Degree C)

           97      72      66     64 

Izod Impact   .51      .88     .63    1.18

Sample A & B were cured 16 hours at 25 degrees C then 3 hours at 100 degrees C

Sample C& D were cured for two weeks at Room Temp.

Conclusions:

1. 2:1 by volume mixes give greater strength that 1:1 by volume

2. Heat-curing gives greater strength than Room temp curing

3.  Heat  Deflection  temperature  is  higher  on heat-cured mixes which means it takes a higher temperature to soften the epoxy and make it plastic. Some epoxies have a narrow softening window. Get too hot and they breakdown quickly. The significant increase in HDT for the 2:1 mix, heat-cured, suggests why Bill Harms (at 1.5:1) and others (at 1:1) find it easier to straighten after room temp curing or even heat-curing.

4. Izod Impact is a testing technique to evaluate brittleness of a material. The 1:1 mixes have a higher impact strength. They are therefore more flexible, less brittle. That goes hand in hand with the other characteristics. And, typically, when you mix epoxies at ratios other than ideal, i.e. with a surplus of either resin or hardener, you get a softer, more flexible material.

Hope this sheds some light. (Al Baldauski)

Thanks much for that information. It's very informative and useful -- and very similar to what the Miller-Stephenson literature suggests.

I wonder, though, about your conclusion #2 -- comparing the strength of a heat-cure to a 2 week room-temp cure. Based on the data you provided, it seems that 2 weeks at room temp. is probably not be enough time for the glue to reach a full cure. My understanding is that a heating regimen only accelerates the catalytic reaction needed for a cure, but does not alter the glue's final properties over conventional (non-oven) curing. Do any of you "chemical-heads" out there know about this?

But, the question is, what amount of time IS required, for a given mix-ratio, at room temp. to obtain a complete cure? (Concrete, for instance, requires several years, so it's not so great for fly rods.) All largely academic issues, since most of us probably will continue with our ovens. (Bill Harms)

Two weeks at room temp is probably adequate to achieve full strength. If you compare samples B & D you will see that they are nearly the same despite the fact that B was heat-cured. This implies that a 1:1 mix , which is overly rich in hardener, will achieve a certain strength either way. Whereas, a 2:1 mix, the perfect ratio for the chemical reaction, achieves the highest strength because of heat-curing.

The 1:1 mix achieves nearly complete reaction of the resin molecules by using excess hardener. That's why there is little difference between heat-cured and RT cured samples. But, the excess hardener is unreacted and acts like a lubricant between the molecules of cured material, reducing its ultimate strength but making it more flexible.

Unlike cement which relies on moisture to fully cure, the perfect ratio of resin to hardener molecules is necessary for maximum strength. However, If all of the molecules cannot come together to satisfy the chemical balance, then you never reach full cure. As the epoxy reaction proceeds, the material becomes thicker, thereby reducing the mobility of the molecules. At some point the viscosity is so high that reaction sites on the molecules cannot get together and you never reach a complete chemical reaction. Heating the material decreases viscosity, increases reactivity and thereby promotes a more complete chemical reaction. Something that cannot be achieved with time. (Al Baldauski)

Excellent information, and well explained!! A powerful case for the heat-cure regimen, as well as AGAINST using the 1:1 mix-ratio for our purposes. It sounds as if the 1:1 mix, aside from not reaching as complete a cure as the 2:1 ratio, may account for what some folks have called "creep" in epoxy glue lines -- a function of excess hardener continuing to serve as a "lubricant"  between  the  other, cross-linked molecules. Not exactly what we want, and something that may allow for easier "sets" later on. (Bill Harms)

That's my conclusion. Although, higher strength from heat-curing leads to more difficult straightening. I don't know what happens to the structure of this epoxy when you significantly exceed the Heat Deflection Temperature. If there is a broad range of plasticity at elevated temperatures, before molecular breakdown, then straightening should be achievable.

I just found some additional data on the Reynolds Performance web site which supports your mix ratio of 1.5:1. For Epon 828, they have a list of 20 or 30 different kinds of curing agents. Under 3140, they recommend 1.5:1 as the preferred mix. At this ratio, the heat-cured material has a Heat Deflection temperature nearly 20 degrees C higher (115 degrees C) than at 2:1. This suggests that you get a greater percentage of cross linking at this ratio than at 2:1. This is possible since excess hardener provides more "available" cross linking sites when the epoxy becomes very viscous. The extra cross linking overcomes the "lubricating qualities" of the slight excess of hardener. They don't provide any other mechanical properties at this ratio, though.

So, 1.5:1 may be the optimum blend. Given this additional data I would tend to think so. (Al Baldauski)

Thanks, by the way, for your great demo of brush varnishing in Power Fibers a while ago; very clear and well presented.

I guess that what you say about variations in Epoxies and their hardeners will account for many variations in characteristics. I am using Epon with a locally supplied hardener whose alphanumeric designation I cannot now recall, and the ratio of mix is 3:1

I achieve what the company says is full cross-linking by curing in my fan-forced heat oven, and I am very happy with the final result.

However, my experience is that I can still straighten pretty easily at an time. In one recent case, I sold a rod to a friend and had obviously forgotten to straighten one tip- Senior Moment, I think- and he brought it back after a couple of months, at which time straightening was the work of but a few moments, using very little heat at Setting #2 on my Bosch heat gun.

He has, at my request, been preferentially fishing this tip hard since (I guess I was worried that I might have struck one of those sections one is always hearing about where they just take sets for no apparent reason) and the section is fine.

Must be the variation in formulation. (Peter McKean)

The last tip I had to straighten and untwist I tried a different trick: wrapped it in a towel and poured boiling water onto that. After a couple of minutes a cold iron unkinked it and the put it in the planing form and clamped it straight. There's no telling how many other tricks have been tried, perhaps incompetence is another mother of invention. (Henry Mitchell)

Talking of tricks for straightening I still use the tool mentioned by Max from Japan a few years ago, even though I do not remember the technical name.

It is a piece of 4" by 4" timer about 18" long with 3 grooves cut in one face. The grooves are about 1/2" deep and on mine one groove is about 1/4 " wide and the others 3/4" and 2" . The rod section is heated with the heat gun in the usual way until pliable and then slipped into one of the grooves. The groove holds the rod section enabling it to be bent to the required angle and it is easy to hold in place. It sounds complicated but is very easy to do. The different width grooves enable different angles to be obtained easily and the bulk of the wood provides stability which Peters "finger tweaking" does not always.

Try it on an old piece of wood with a rod section, it is surprising how easy it is to adjust angles. (Ian Kearney)

Tamegi - see here - the bamboo tips site, under contraptions, straightening devices. I use these sometimes on strips, but tend to rely more on the vise. (Chris Obuchowski)