If you take the same dimensions on two identical bows BUT, one has .040 'glass and the other .050 'glass what would the weight difference be? From what charts I have looked at it looks like almost 10 pounds which is a lot.
It's gonna be close to ten, is on a bow off my form anyways. A lot of strength in the glass.
Cory
I agree with Cory.
You will need to increase your total stack thickness proportionately more when dropping from 0.050 to 0.040 glass.
It seems draw weight relies heavily on the glass thickness. More so than one would think. We spend a lot of time discussing stack thickness and lam combinations on this forum... and it seems that on a straight limbed longbow .01 of glass = pretty close to 10#. Of course varies with bow length and limb dimensions. I know there are no hard, fast rules but from what I have read this seems to be pretty close.
I have had a few request for some younger folk's bows. I need to make my 10 year old daughter a new one also. I was wondering about this and what stack thickness I would use for a 60" mild r/d bow around 30#. Thinking around a .250 using .040 thickness glass should get me close at 1 1/4 wide limbs. What say ye?
The glass thickness itself is not so important for the draw weight. The total stack is what's important. In fact I have I have built the same bow with different glass thickness but the same total stack and I haven't noticed any significant difference in draw weight. But since glass is much heavier than wood/boo lams there are differences in performance. The limbs get heavier when using thicker glass and therefore the bow will cast slower and hand shock will likely increase.
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Andy
Thanks Andy. Good info!
About 88% of the strength of a wood-glass composite comes from the glass; only 12% from the wood. As mentioned, it's not glass thickness, per se, but total stack.
If you have a for for a bow and have made weight and length X in that style, you can use the Lam Stack Calculator (that can be found here at Trad Gang)to calculate the lam stack and length for a new bow of the same design. Worked just fine for me recently on both recurve and flatbow designs that I'm finishing and will show when they're done.
KenH, i'm not real computer savvy, when I go to the link it says "upload file" I don't know what file name to put in to open. I know this is stupid but can you talk me thru this? I really would like to play with some stack thicknesses but don't even know where to start. I have downloaded openoffice although i do have MS office as well.
QuoteOriginally posted by Swissbow:
The glass thickness itself is not so important for the draw weight. The total stack is what's important. In fact I have I have built the same bow with different glass thickness but the same total stack and I haven't noticed any significant difference in draw weight. But since glass is much heavier than wood/boo lams there are differences in performance. The limbs get heavier when using thicker glass and therefore the bow will cast slower and hand shock will likely increase.
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Andy
Thats good to know, like they say learn something everyday........
QuoteOriginally posted by critman:
KenH, i'm not real computer savvy, when I go to the link it says "upload file" I don't know what file name to put in to open. I know this is stupid but can you talk me thru this? I really would like to play with some stack thicknesses but don't even know where to start. I have downloaded openoffice although i do have MS office as well.
X 2
Critman and Mark -- check yer PMs...
Critman,
Using a "Kenny M" R/D design form for a 58" bow, this is what I have come up with after experimentation: .030 Glass, .130-.002 Taper Back Lam, .070-.001 Taper belly lams. Bow scales right around 26-27 lbs @ 28".
Thanks quail. Is that the mild R/D or more reflexed design of kenny's?
More R/D design. Bow shoots really nice!