Heat treating demystified (Somewhat)

[Buckeye Guy]

I feel a strong desire to post on this subject , yet the wisdom of years has taught me there is so little that I can actually prove, and so much that I have forgotten or remember only as I want it to be !
 I refrain from stating things as fact ,as long as I catch myself first,yet there is so much to think on that happens inside of our bows !
Demystifying all of that, most likely will not happen.
 We could be left with out any reverence for this awesome thing we jokingly call our addiction !!
Info sharing is a strange bird in and of itself with all the preconceived notions we carry into our outlook on things!
Lostarrow seems to be saying basically the same as I was told way back when .
Heat definitely changes wood as we can see what is being done today to treat wood by heat instead of chemically to slow down the decaying process ! And then there is its use for musical instruments and such!
Marq has a tryed and proven way to do a bow and yet we want to know how to do variables !
So much to do and so little time ,life is short !
Have fun folks and enjoy an awesome pastime !!
Guy

[richgibula]

I know that its been a while since someone posted here last.  I just got into bamboo but I am using laminated strips.  I am getting good results but I have questioned the heat treating process. I have not done that yet but I have experimented.

I tried a heat gun but it took a really long time so I tried a torch. There is a really fine line between brown and black in a 1 mm laminate.

The important thing I discovered in my experiments is that the browned bamboo was definitely stiffer than the untreated ones, hands down.  You can easily see this when applying pressure to arch the specimen.  It even made me worry that the heated one might not bend enough for my recurve mold shape.  I did eventually test that and it will flex far enough. I am not sure how that translates into bow characteristics but I know that my stiffer bow woods have more spring that the softer woods.  When I make my next bow from bamboo laminate, I will be able to compare draw strength with non-heat treated bamboo I have used until now.

The next issue is compassion strength after heat.  The studies I read say that it goes up but I have no way to objectively compare that.  Maybe someone has an idea.

The other important item is fracture strength.  I partially heat treated a number of laminate pieces and flexed them into a circle until they fractured.  Every piece, no matter how I made the circle tighten, fractured at the untreated portion first rather than at the heat-treated part. This may not be a fully scientific process but at least the treated laminate does not fracture easier than than the untreated one.

I anyone has any more information on the subjects of MoE and compassion strength in dried bamboo, I would love to hear from you.

[bassman211]

The wood most commonly used to make bass, and guitar necks is rock maple. The new trend now is to toast the necks at the factories. They end up a sort of amber color, and are supposed to make the necks more stable under changing climate conditions. Their is a steel truss rod  that runs through the neck to makes adjustments for warp age to a certain point. . I bought an 1983 Kramer bass that was stored in a basement for decades, and the neck looked warped beyond repair, but because of heat treating bows, and seeing the magic it can do with hardwoods I took a shot at building a jig , heat treating the neck, and clamping it back to straight. It worked fine. String action is excellent, and the neck has stayed stable, and the instrument plays beautifully. I will leave the science to you guys, but my bow building has made leaps, and bounds, because of the use of the heat treating process especially with white woods when it comes to bow building.

[superdav95]

Rich.  I have done a fair bit of my own research and testing on the heat treatment of bamboo specifically.  It does benefit from proper heat treatment. It all depends on what type of bow you are building with bamboo and where on the bow the heat treated laminate is placed.  A good scorched belly belly lam works well.  James Parker has made many many of these.  I’ve recently made some experimental  boo bows that are bamboo backed and belly laminated with heat treated lams.  It’s crucial to not exceed 180 degrees in my testing.  It’s moe drops off at higher temps. I found this correlates with some research papers I found on heat treatment of bamboo laminations for building purposes.  I heat treat my lams by using radiant heat element to lightly toast the belly for about 30 mins.  I also toast the back lightly to assist with removal of some moisture.  You’ll see the moisture escape the ends of the lams while doing so.  I then place the lams into a reflex if doing a simple single layer boo bow with power fibers as the back into a convection oven for a few hours at 170-180 degrees.  I have done extensive fail testing at higher temps with lambs and they pulled splinters or broke altogether.  I use mosso pole bamboo.  Test pieces were all between 1 3/4”-2” wide by 25” long.  Strength increased greatly in the samples and the weight dropped also.  It’s recovery to it’s relaxed state was also better.  Set was greatly reduced.  I observed the belly of the bamboo to also be harder as it was harder to dig my fingernail into.   I’ve build simple 5 piece bamboo self bows with this heat treatment method with great results.  I was impressed with results of such a simple bow design.  Hope this gives you some idea for bamboo.  I could give some more details on the process if needed. 

[richgibula]

So, superdav,

You don't think that you should heat to a brown color?

[superdav95]

Correct.  Especially the power fiber side of bamboo.  You may get away with it more toasted in the belly but even there I’ve had failures.  The odd one will survive but it’s no noticeable gain that I’ve noticed going darker toasted Color.  It’s the lignins and pectins in bamboo that caramelize or harden with in the cells of the wood that give it more compression ability.  Tension is already pretty good on dry bamboo and so heat treatment used on the outside surface is risky in my opinion and experience from my builds.  The main benefit may be the loss of mass or moisture content.  I always measure my before and after weights when heat treating bamboo and do notice a difference in overall mass.  There is some acclimated moisture that returns but never to the same degree it was at all.  I seal mine soon after heat treatment too to prevent too much mc creeping back.   

[richgibula]

Thanks for that info.  I was asking because you get more attractive looking wood with more toasting, but not at the expensive of wood integrity.

[Badger]

     I don't really have much to add to this beyond just personal observations that sometimes contradict themselves. For example, many dense tropical woods I have worked with don't seem to benefit from heat treatment with a couple of exceptions. One of them is massaranduba, but in its case, it is also known to have issues with water retention. Osage responds very well to heat treating and it does resemble the tropical woods more than it does most northern hemisphere woods. I am convinced that moisture removal and improvement in the ability of the wood to stay dry is a major factor, especially in white woods. But I also believe there is some plasticity gained by heat treatment. I never wait for a bow to rehydrate after heat treatment. As soon as it cools I tiller it. I have never had any issues with them losing draw weight after they acclimate.  I tend to leave them about 3# heavy if I finish them right after heat treatment. Hoping when they rehydrate the weight will go with it. I never does change, and I always have to go back and take off the 3#.