Author Topic: Bamboo tri lam questions  (Read 1644 times)

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Offline Lee Lobbestael

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Bamboo tri lam questions
« on: January 07, 2017, 11:53:07 pm »
I have never done a tri lam bow before but would like to try a bamboo backed and bamboo belly with a maple core. Can you sand the nodes down and flatten the bamboo on the belly of the bow?? Otherwise I'm not sure how I would tiller it. Also the bamboo straps that you can order from 3 rivers, do they need to be tempered? I have a big oven at work I can use to do this.  How long and how hot should I go with it? Thanks

mikekeswick

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Re: Bamboo tri lam questions
« Reply #1 on: January 08, 2017, 03:56:11 am »
You tiller the core. Contact a glass bow builder and ask for a set of 0.005 tapers (I would grind you a set but you would have to pay postage from England....) and combine these with a 6 inch parallel width then taper to tips. Any tillering after glue-up is done to the bows sides but you can't go far with this hence the need for an accurately tapered core pre glue-up.
Temper the belly piece to near black.

Offline aaron

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Re: Bamboo tri lam questions
« Reply #2 on: January 08, 2017, 11:58:27 am »
I have always wanted to do a BBB like this! Mike, can you give a little more info (or a drawing) of what you mean?
Ilwaco, Washington, USA
"Good wood makes great bows, but bad wood makes great bowyers"

Offline Pat B

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Re: Bamboo tri lam questions
« Reply #3 on: January 08, 2017, 12:40:13 pm »
Like glass bows bows with boo back and bellies have to be engineered before glue up. Like Mike said tillering is done from the sides and that has limits.
Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC

Offline Lee Lobbestael

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Re: Bamboo tri lam questions
« Reply #4 on: January 08, 2017, 05:52:04 pm »
Hmm sounds beyond my capabilities

Offline Springbuck

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Re: Bamboo tri lam questions
« Reply #5 on: January 10, 2017, 02:34:47 pm »
Naw, you can do it, Lee!

It's not going to be exactly the same, but find a bow you like the looks of and copy it.   Get general measurements.   Something like a pyramid bow is pretty predictable, despite the front and back crown.   Get good, wide bamboo and carefully shape and flatten the backing.  Leave the belly parallel, but the nodes will be there obviously.  I knock the nodes down, but don't mill them totally smooth in line with the rest of the bamboo.  Worked down, not totally leveled.   Get the pith side flat enough that the bridges of the nodes disappear.

  When you temper the belly lam from the outside with a heat gun, the bamboo usually flattens laterally, slightly.  I mean it will start off looking like it came from a 4" diameter stalk, and have the curve of a 5" diameter stalk at the end.

  One good trick is a two stage glue up. Glue the tapered core to the bamboo belly, shape the front profile roughly, and give it just a few inches of flex.  Remember the old rule of thumb about "twice as thick is eight times as stiff"?  Use that as a general guideline.  If the bow is 3/8" thick at the handle and 1/4" thick at the tips, but bends too much out at the tips, maybe your bamboo back should be 1/8" thick all along.  That adds 33.33% more thickness by the handle, but 50% to the tips, adding thickness PROPORTIONALLY .  If the middle bends too much, taper your backing so you add more to the inner and middle.

Design rules apply.  If you have strongly crowned bamboo, make a narrow longbow type.  I also matched up my slats and placed belly nodes between back nodes rather that straight across.

Then hack your way through side tillering.  Good luck.