Tempering Bamboo Backing Discussion

[blackhawk]

My little futile mind is turning some thoughts and ideas about tempering and heat inducing reflex into a strip of bamboo intended for a backing strip. Now I know the general consensus is not to temper bamboo backings,so you don't have to come on and reply not to do this. But,here me out. I'm cooking up a laminate recipe right now and these ideas have come to my mind.

What if you lightly tempered the backing strip into reflex from the inside of the bamboo while the bamboo was slightly thicker than finished thickness? And make sure not to drive the heat to far down into the power fibers,but enough to change its memory shape. Then go ahead and finish sand to finished tapered thickness.Now I know gluing it into reflex changes its memory because the glue line holds it there,but wouldn't this give a teeny bit more of resistance upping performance by a teeny weeny bit? I'm curious to see what y'all think?

[JonW]

Will you be gluing in more reflex than what you induced with heating it? Seem like if that's the case you may not see any difference. Just a thought from a simple mind.

[PatM]

 Quite a few flyrod makers use the temper from the inside method. Flyrods are also often tempered from the outside to the point where they look almost charred. It would seem that the Tonkin cane they use is a bit more heat resistant.
 Not sure how much the actual manipulation of the backing strip into reflex before glue-up will make a noticeable difference.
 Tonkin for example already has very similar properties to fiberglass so making it even "better" and more stress inducing on the belly material seems like it might cancel out your gains.

[Pat B]

If the boo backing is thin enough it should conform to most moderate shapes without much trouble so I don't see a reason to temper it. For me it would not be worth the risk of weakening the boo backing for this.
  I have seen where folks add coloration to boo backing strips with heat though.

[blackhawk]

I understand that if its thin enough it'll conform to most shapes gluing it in. When I said teeny weeny bit,that's what I'm talking about,if it would make that small of a difference to add a couple fps more. While it may not be worth a risk for most,if it does make that much of a difference it might be worth it for someone wanting to shoot that extra foot. What if the boo was tempered into monster reflex like 10"+,then glued in with not so much reflex? Wouldn't the boo have a little more "prestress" in it even if it now has a new memory after the glue line? I realize I'm talking very minimal gains,but I'm trying to figure out if there would be some gain even if it is small.

[Shaun]

I believe tempering and heat shaping are two different things, though sometimes both happen when dry heat is applied. Heat shaping only requires heating until the wood cells soften and "give". Tempering is slower "cooking" of the wood to change its properties.

[LJB]

Hi,

maybe i am not on the right track here but, as far as i am understanding things, the effect of gluing in reflex ist (partly) gone when you heat reflex it before gluing up.
When gluing in reflex the back gets compressed, this is the advantage of the perry reflex. You got lots of movement before the back gets into tension again.
With the belly its the same, when gluing in the reflex, the belly gets under tension first. It will not be compressed before the bow is drawn beyond the original shape of the laminates.

[blackhawk]

I understand the difference between heat shaping and tempering. What I meant was that tempering it and reflexing it to the point where it does stiffen the bamboos bend resistance and makes a change,but still not drive the heat to far to make it brittle.

Yes ljb that is the whole point of Perry reflex,but if its now done with boo that is more " bend resistant" than an uncooked piece of boo wouldn't that give you a "small" advantage?

[blackhawk]

My thoughts and ideas stem from what some folks and I have done as well. And that's tempering and inducing a part of the reflex in the belly wood pre glue up. In my opinion this does help and its why I'm thinking if it would help in a small way to do the boo backing as well if done right.

[RyanY]

If I'm not mistaken Marc St Louis heats reflex into his belly lams and then adds more reflex when gluing up. If it works for the belly I can't see why it wouldn't work for the back too as long as it doesn't compromise the integrity of the fibers. If my understanding is correct, it would almost be like you're gluing up two reflexed lams into just a bit more reflex.

[PatM]

The "compression" on a backing strip is insignificant when doing a glue-up. The piece is never flexed enough to actually cause any squeezing of the cells.  The average backing strip probably only has ounces of "draw weight" when bent into the reflexed position.
 I can see you getting that extra little bit of performance from a heat treated into reflex backing. Everything we know about bow design tells us that but you will walk the tightrope of brittleness in tension.

[blackhawk]

Well..I went ahead and did it..heck, why not right? Its not like I neeeeed another bow and can't make another if it don't work out ....I tempered in an unclamped 2 3/4" of reflex into it...I tempered as I normally wood a stave and to the point where it was to hot to the touch on the back...I don't think that would hurt the power fibers on the back cus it doesn't hurt it on a stave,and the heat didn't wrap around and scorch anywhere on the back either..I think its aok. Ill glue in just a hair more setback and see what happens...

Thanks for all the input so far everyone.

[Marc St Louis]

Bamboo is plenty strong in tension by itself that it doesn't need any heat-treating but it shouldn't hurt anything doing it either.  It's the belly that benefits more from heat-treating than anything else

[BL]

Crazy, counter-intuitive thought.  Heat-shape extra DE-flex into the backing strip so that when you glue in your normal amount of reflex, you might actually get some compression stress during glue-up?  Like Perry reflex but you'd have to go backwards to up the initial strain for bamboo?

[BowEd]

blackhawk......My thoughts went the route yours did here only I was glueing horn to the belly of a bow.I did'nt heat a curve into the horn that time prior to glueing.I just did the usual glue up induced reflex it only kept half of what I induced before tillering.Next time I think I'll match or a bit more the curve the limbs have dry fitted [through reverse bracing]and then see if it holds more reflex.I'm imagining it will to a certain degree.Doing this before aplying sinew on the back.To me it will increase performance some because it's putting more stress there.A bow at it's max stress point before release is at its' fastest.Closer to the edge as they say.Same thing will be going on with your future bow.
To me it's like chasing a ghost doing this or groping in the dark to see what happens but still fun.Good luck.