Glass Weight Differences??

[matts2]

I was chatting wit Byron Ferguson this weekend and looking at some bows him and his son build.  He said they use nothing but .050 glass which keeps his lams minimal.  Normally all their bows had two lams with maybe a power lam in the middle.  I am curious what kind of differences in weight there would be with a bow if it had .030, .040 or .050 glass on it?  I really like the bows he had and the short stack limbs.

[Robertfishes]

I am using the kennym design 64" form..I have only used 040 glass and a stack height of. 360-365 measured at the center of bow lam stack. My bows ended up 42-49 lbs @ 28 inches at that stack height. I have not used any tip wedges or power lams..

[Bradford]

I have been using the black .030 glass.. and thicker wood stack.. still works out the same, but yes, more wood.

The stack will be the same.. but with say a clear glass, you would not notice that .050 as much as an extra .020 of wood each side.

[Swissbow]

If the total stack ( wood + glass ) is the same, there should be no significant difference. Generally the glass to wood ratio should be around 20 - 25% for a longbow. No you can play a little bit with those numbers. You could say that if you use tapered lams then the ratio would be higher at the tips, since the glass is not tapered and therefore you might tend to go towards 20%. Or you could say that you want to stay on the safe side and therefore you choose the glass so that the ratio is closer to 25%. It would be interesting to see if there is any difference speed/performance-wise if one build the same bow only with different glass to wood ratio. Personally I tend towards the 20% glass to wood ratio. But I don't have any results to prove if I'm right or wrong.

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Andy

[Murkar]

I asked the same question to Bingham Projects a little while ago because I was unsure about it and am planning to build a glass lam recurve.

Here is the response I got from them copy/pasted:

"Thanks for your e-mail.  For a given limb thickness, there is no difference in draw weight with different thickness of glass.  If the total limb thickness is the same, the weight will be the same.  The best way to most closely hit draw weights is to use a micrometer to measure your limb thickness.  If you measure to .001”, then your weights will be pretty consistent.  It will never be 100%.  There are always those bows that surprise you but the vast majority will be pretty consistent."

Hope that is helpful to you  

[matts2]

Mixed answers from all over really.  Some say the overall limb thickness is the only driver to weight.  Others say that glass has different weights on thickness then woods.  

If I have a bow with total stack of .350 and .030 glass, will it be the same weight of a bow with a total stack of .350 with .050 glass?

[Bradford]

In theory, yes.. that is what is taught..told.

Kenny M did a great thread on different woods and the performance was all pretty close.. so I am to ascertain that glass thickness would have the same effect.

[Zradix]

This thread is an eye opener for me!
Thanks!!!