Author Topic: Bamboo thing/question  (Read 1293 times)

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Offline DC

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Bamboo thing/question
« on: June 01, 2020, 08:26:23 pm »
I had occasion to remove the backing from a couple of bows. I was planning to put a skinny lam in between belly and back just to put the weight back up where it should have been if I hadn't screwed up. I heated to Boo and slipped a knife between the Boo and the belly and then twisted the knife a bit to pry the back off. It was going well and I noticed that the backing was was going into big time reflex, like a horn bow from the heat and the little bend the knife put in it. Anyway, when I looked at it, it had cupped a little. When you glue on a backing the side toward the bow is flat so you get a nice glue line. Well now it was curved on both side like a convex lens. In order to get a nice glue line I had to grind it flat again. So now the bamboo is only about half as thick as it was. Is this a good thing? It would be lighter. Would it be worth doing deliberately to get a thinner backing from a smaller diameter boo log?

Offline mmattockx

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Re: Bamboo thing/question
« Reply #1 on: June 01, 2020, 09:50:06 pm »
Would it be worth doing deliberately to get a thinner backing from a smaller diameter boo log?

Seems like that would be worthwhile to me, but I have not used bamboo backing (yet). Considering how much stronger and stiffer it is than most woods, making it flatter and thinner would make it easier to balance the forces with the belly wood.


Mark

bownarra

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Re: Bamboo thing/question
« Reply #2 on: June 02, 2020, 12:07:58 am »
It doesn't really make much difference to anything.

gutpile

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Re: Bamboo thing/question
« Reply #3 on: June 02, 2020, 07:36:59 am »
I imagine when you go to glue it back up your clamps would eliminate the cup and glue would of held it... just my thoughts... gut

Offline willie

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Re: Bamboo thing/question
« Reply #4 on: June 02, 2020, 10:28:40 am »
Quote
making it flatter and thinner would make it easier to balance the forces with the belly wood.

DC, you didn't say what you were intending to put the backing on.

there are questions in a nearby thread about how much boo it takes to balance the forces with ipe. To me, knowing how much boo to apply to any particular belly should be an important consideration.

I guess no matter how much is desired, the flatter and wider would make more sense. 


bownarra

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Re: Bamboo thing/question
« Reply #5 on: June 02, 2020, 12:07:35 pm »
Reckon i'm upto around a hundred or so boo backed bows from elbs, plain flatbows to r/d. In the beginning I tried thicker thinner etc backings with this and that wood and found no noticeable difference. Now I found that a hand tillered boo backing made reasonably thin but not overly so combined with a tapered core is the way to go. Trapping the back if the belly has lower than desired compression resistance is the only effective way with boo.
Thinning backings to try and lower their stretch resistance for matching of bellywood properties is a waste of time. It is only the outer 1/16th of a limbs wood that does any work, back or belly. Altering what the 'spacer' is between the working sections of limb has little effect on those surfaces opposing forces.
There is the potential to make the core out of a lighter wood thus saving a little limb weight but again these things have very little difference.  One thing I will throw out there (and see if anybody gives it a go :) haha) is having a core that doesn't resist bending as strongly as the core wood in a normal limb has very interesting effects. This can be achieved with the use of a laminated end grain core. I'd love somebody else to try this one! The simplest way is with a pyramid, tri lam flatbow :)
Tillering skill and keeping set low trumps most other things in the finished bow.

Offline willie

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Re: Bamboo thing/question
« Reply #6 on: June 02, 2020, 04:47:34 pm »
Mike, I appreciate your sharing of experience, practical experience from testing different stuff.

the end grain idea is interesting. Before the fg guys used foam core, there was balsa core. that might be too light for a bow, but I could see willow core or something similar.

Offline Selfbowman

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Re: Bamboo thing/question
« Reply #7 on: June 03, 2020, 10:48:23 am »
Bownara I have not built but maybe 6 bamboo backed bows. It does not take much boo to go along way. The first boo backed gemsbok bow I tried to hit fifty pounds it came out 108#. Hahaha so I tried less core and managed a thin fifty pounder. Also I used tapered boo flooring for the core lams. Great combination!  Arvin
Well I'll say!!  Osage is king!!

Offline Marc St Louis

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Re: Bamboo thing/question
« Reply #8 on: June 03, 2020, 11:48:02 am »
I've re-used Bamboo backings before
Home of heat-treating, Corbeil, On.  Canada

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