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Heat treating bamboo backing strips?
Eric Garza:
When folks make bamboo-backed bows, do you heat temper the bamboo backing strips? If so, do you heat-temper them before you sand them down for glue-up, or do you sand and shape them first?
Hamish:
The traditional theory is don't temper a boo backing. Tempering is traditionally used for belly facing or laminated belly staves. Tempering increases the compression resistance of boo, but makes it more brittle in tension.
You can temper the boo, in full thickness or partially worked down. I wouldn't temper at final thickness as it will cup and you might get charring on the edges.
You can put boo backing in a hotbox to drive out excess moisture.
superdav95:
Eric. I have tempered my boo backing strips. As hamish says mainly to get rid of moisture. It also provides more strength but at a risk. I have made many attempts and failures. The biggest thing was figuring out the thicknesses. I have heat treated my belly lams too. I have a few bows done now with using this method and they can be hit and miss. When they miss they go bang and when they hit they work very very well. I would go easy with the heat on the backing strip. I use my belt sander to get the strip down to about .150-.200” thick. If using typical 2” wide strips from echo or elsewhere online or if making your own from poles select the very best quality of backing with the least amount of irregularities at the nodes. Space out your nodes well to account for more even stresses on both limbs. I use a radiant heat source to temper my backings and go until it darkens the belly of the strip a little. Just little toasted. I do not toast the rind side at all on these builds. You will see steam exit the ends as you do this. You will also notice that the flat sanded surface of your strip will have rounded or crowned. I also like to weigh my backing before and after temper to observe water moisture loss. I then take this down from here to my final dimensions depending on build. For a long bow that’s fairly narrow around 1.25-1.3” wide at fades tapered out to the tips I’ll make the thickness at handle area about .125” thick and gradually tapering out to the tips at around .090-.095” thick. It’s important to keep it pretty thin otherwise you get a boo strip that overpowers the belly wood. Once I get the tapers looking good I trace it out on my bow the way it will sit. It’s best to choose good boo strips. The less natural crown on your boo the better. This way it will less chance of it overpowering you belly wood. Another thing to remember is that boo adds a lot more draw weight then you think. Always go thinner then you think when building and laying it out. I use ea40 mixed according to can instructions. I’ve posted a few of these build here on pa over last year or so and they all held a crazy amount of reflex and are very fast bows. You need a stringer to safely string them but once they are strung and tillered well they make very fast bows. I’ll see if I can dig up one of my earlier posts from this year. Reach out if you need to. I don’t mind sharing what I’ve learned with these bows. Best of luck. Here’s a link to one of these bows from few months ago.
http://www.primitivearcher.com/smf/index.php/topic,72796.msg1021113.html#msg1021113
Eric Krewson:
Years ago, there was guy in Texas that was selling what he called Tonkin bamboo, being younger and not as worldly as I am now, I bought some. This bamboo had been flame tempered, the back was dark brown and the tips of the nodes were slightly charred.
Compared to the standard Mosa I had use up to this point, this bamboo was very strong and made superior bows. I ordered more and the guy sent me junk slats with cracked backs. When I questioned him about what he sent he got nasty, I realized he wasn't an honest person and later found out that Tonkin cane never got bigger than 3" in diameter and there was no way this was Tonkin anything. I suspect these slats were flame hardened Mosa, the backs were almost flat so it came off of large diameter bamboo poles.
If you watch the Japanese bow makers on you tube you will see that they flame harden their bamboo and have been doing it for thousands of years so there must be something to it.
Eric Garza:
Thanks for the responses! I have another question: Is there a benefit to using bamboo backing strips with fewer nodes on a bow, or does it not matter?
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