Glass lams and weight

[michaelschwister]

Okay, after 20 some years of selfbows I decide to go to glass lam bow building.  It sure is much easier, but hitting weight is pure frustration.  After 5 bows on the bingham 64" R/D form, I made a new form and worked up the perfect bow I have been thinking about for more than 20 years.  I do the math and went for 60#, and got 72# roughed to form and 68# after heavy sanding.  The first one used .050 clear glass back and belly, 3x black locust lams .090 tapered .002 put in two tapers and one reverse, and then a .030 uniweft core. So  I do the math and use .030 glass back and belly with the same combo of Core to get around 60#, SHAZAM 41# after grinding to template??? WTF??

I want to make a 48#@28" for a buddy and want 57-60# at 28 for me.  How do I get there???

[Troy D. Breeding]

Michael,

I only use .040" glass. Never used uniweft so can't help you there.

I'd suggest using .040" glass and adjusting the core thickness.

Troy

[Crooked Stic]

You got to figure out how many thousands you are adding or taking away to = 1lb. Then adjust from that.

[kennym]

Just changing from .050 to .030 glass, even with same total stack will make a bunch of diff.

How much will depend on bow design....

[jess stuart]

PM sent

[michaelschwister]

I still have 2x .050 and 4x .030 clear glass.  Just ordered 4x .040 and two more uni cores.  The one I just finished gets 50# at my buddies 30" draw (I read 41# at 27"), so he may  like that weight. I will try a .040 on back and .050 on belly to try for low 60s.  I bet .030 back and .040 belly would get high 40s at 28".  Bingham says sand off back glass to lower weight, so I figure that is where to put the thinner glass?

[Bowjunkie]

I usually use 0.040 glass belly and back. But when I did use two different thicknesses of glass, I put the thicker on the back. I wasn't sure why, its just what I was told to do once by a very respected bowyer. Knowing now that glass fails in tension first, it sems like the right thing to do. That way you'd be able to sand a little weight off if you so choose. I REALLY don't like doing that though. Rather, I keep detailed records of every bow to be able to nail the weight on succeeding bows. If you only change one thing at a time, you'll soon see how much weight you gain or lose by changing .010 glass thickness, changes in riser length, bow lengh, lam stack thickness, by trapping, etc... as relative to YOUR design parameters.

[michaelschwister]

Great information here, thanks guys.  Good news is my buddy says 50# @ 30" is perfect. I now am keeping detailed records, but this is bow 7.  In the early 90s I made up a detailed log book for making glass laminated bows, just could never stop making selfbows, the around 2000 got hooked on BBOs. A guy can go through alot of money getting the right skills on these bows! Selfbows you just go to the woods and cut some more.  Thanks to Troy Breeding for cut the Black Locust lams for me, they really perform well.

Mike

[Swissbow]

How wide are the limbs at the fades of the riser and at the tips ?

----------
Andy

[bamboo]

Originally posted by michaelschwister:
Okay, after 20 some years of selfbows I decide to go to glass lam bow building.  It sure is much easier, but hitting weight is pure frustration.  After 5 bows on the bingham 64" R/D form, I made a new form and worked up the perfect bow I have been thinking about for more than 20 years.  I do the math and went for 60#, and got 72# roughed to form and 68# after heavy sanding.  The first one used .050 clear glass back and belly, 3x black locust lams .090 tapered .002 put in two tapers and one reverse, and then a .030 uniweft core. So  I do the math and use .030 glass back and belly with the same combo of Core to get around 60#, SHAZAM 41# after grinding to template??? WTF??

I want to make a 48#@28" for a buddy and want 57-60# at 28 for me.  How do I get there???

[bamboo]

mike
it sounds to me like you have to start over-but
not all the way !!if your form is built to binghams print its fine
I started with binghams and they are very helpful
my suggestion is to go back and read the bingham instructions--and follow them--riser length-and taper rates-and stacks given by them are designed to work together-and proven!
forget the uniweft-3 tapers[one reversed]for now!its the only way to get anywhere near being able develop a base design----binghams will spec out a kit for your form and template that will hit close to your target weight-call them-build a few simple bows that hit weight and then tweek your designs one or two tweeks at a time!!and keep records!! it will be easier on your wallet and brain!!sounds like you got a lot of experience glueing up bows--now fine tune it and start hitting weights --its easier than you are making it!!have fun and good luck!!