Author Topic: Yew Belly lam/trilam  (Read 236 times)

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Offline Sagebrush

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Yew Belly lam/trilam
« on: September 20, 2020, 09:19:18 am »
I've been gluing up some tri lamps with bamboo maple and yew.  My question is how thick should the belly lam of yew be??  I have been working with 1/4 inch and thinning it down accordingly.   I guess the best way to express thickness might be a fraction of the limb death due to tapers?  Should it be more than 1/3 the total limb death or should it be more than that?  Like 1/2 the depth.  I'm worried I'm getting thin on my belly lam.  Any thoughts would be appreciated. Thanks guys.

Online PatM

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Re: Yew Belly lam/trilam
« Reply #1 on: September 20, 2020, 09:30:03 am »
It's the part you want taking all the compression so maximizing its thickness and doing the taper through the core makes much more sense.

Offline DC

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Re: Yew Belly lam/trilam
« Reply #2 on: September 20, 2020, 09:43:05 am »
I've made a bunch of Boo Yew bows and ,of course, depending on style, there is very little room for a third lam. On the 50# one I just did at the thickest/widest point the yew is 1 1/2"x 3/8". There is quite a bit of reflex in mine which ups the DW. Closer to the tips the yew is about 1/4" thick. If I was to put a third lam in it would only be 1/8" thick, maybe, and probably tapered. The SG of yew and maple are similar so I'm not sure if the third lam would buy you anything in this case.
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Offline Sagebrush

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Re: Yew Belly lam/trilam
« Reply #3 on: September 20, 2020, 10:05:38 am »
I'm just getting really thin in the outer thirds... I haven't seen a great deal of set yet but I'm only back to 21 inches and 70ish pounds and I'm at a 1/3 of the deapth for the yew.  Set will rear its ugly head soon enough. I'm gonna have to taper the maple to almost nil on the next.  Or as suggested just forego.

Offline Dances with squirrels

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Re: Yew Belly lam/trilam
« Reply #4 on: September 20, 2020, 10:43:38 am »
Kind of tough to answer. We don't know how thick, or tapered, your bamboo is, how thick the maple is or its taper rate. Is the yew starting off tapered or parallel? What area of the limb are you assessing the ratios such as 1/3 of thickness?

When I do it, I start with the bamboo about 1/8" or less at the handle area, 1/16" at the tips. The middle lam is about .200" thick, give or take, and tapered .003 to .004 per inch, with those actual thickness and taper rates depending on limb design, draw weight, and action I want. The belly lam is also about .200" thick, parallel, and again, give or take because exact finished thickness depends on draw weight, design, wood, etc.

It's one of those things you have to trial and error for yourself, cuz we each make and shape things a little different. Taking notes helps.

Mine often start off equal thickness at the handle but with one tapered and one parallel, their thickness at the tips is obviously not the same.
Straight wood may make a better bow, but crooked wood makes a better bowyer

Offline Sagebrush

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Re: Yew Belly lam/trilam
« Reply #5 on: September 20, 2020, 11:33:51 am »
I was trying to take the bamboo down to 1/8th.  The maple was 1/8th with just a bit of taper (my horrible  eyeballed scientific measurement).  The yew was to be tapered accordingly.  In my mind I was trying to convince myself that x% was under primarily tension, y% was primarily neutral, and z% of the deapth was under primarily compression.  I'm sure the ratios change with material to a degree.

I am now at 62lbs at 25 inches with about 1 3/8ths " set after 50 arrows.  This is a 70 inch hill style longbow 1.5 inches wide tapering to the tips. Still faster than heck but I'm sure more set is coming. Aiming for 29 inch draw.