fiberglass advice requested...

[adirondacker88]

Background:

I'm currently attempting to build my second glass long/hybrid bow. First one came out fine but at 62 inches ntn was a bit long for my portable blind and climber. I determined to make a bow in the 58" range. I went with woods I had on hand (a parallel bamboo core lam with two tapered ambrosia maple tapers under clear glass (.040)). Long story short is that even though I lessened the stack considerably from my previous bow that ended up pulling about 50# @29" I ended up with a bow too stout to pull. Solving the stack issue is now a problem to be put off for the next bow .... but I've set a goal to get this one to a 60 - 65  lb. range. Since then I have spent considerable time first narrowing the limbs as much as possible, then "trapping" the belly and finally carefully sanding down the belly glass by about .007.

At that point it was still not something I could draw beyond about 26". I then radically sanded the corners on the belly so that it is now pretty much oval with a half inch width of edge tappered glass left like a stripe down the belly. It is just barely now in a range I can pull comfortably....just. I have shot it 50 + times and the belly seems to be holding up.


I would really like to try and drop another 5 lbs. by probably removing more material from the belly.

My question:

How risky would it be if I ended up removing all belly glass? The back and belly lams were obviously more stout than they should have been to begin with but now that may be a good thing if I decide to remove all the belly glass. I'm thinking it might end up being a 3 piece wood lam bow with a glass back. If I remember correctly maple is generally considered a fair to good belly wood.

Opinions and/or advise welcome.....

[adirondacker88]

Maple lams are 0.120 each at fades with .002 taper. Bambo parallel is 0.110.

[adirondacker88]

lower limb view:

https://www.dropbox.com/s/d5k3omlkb5xnv5g/20140217_190336.jpg

full draw:

https://www.dropbox.com/s/7qmoy13qewhg31f/20140216_140605.jpg

[KenH]

Remember that the glass provides some 88% of the draw weight of a wood-glass composite bow, and the core only provides about 12%.

If you build the same design next time, you can use a Stack Calculator to determine the draw weight you want, based on the draw weight of this bow before you started reducing things....

[bamboo]

sand the back glass too

oh --and don't remove the belly glass
maple isn't a good enough belly wood to take on .04" of glass!

[Crooked Stic]

You will get weight off quicker by sanding the front glass.

[adirondacker88]

Would "rounding" the corners on the back take off much weight compared to taking 0.007 to 0.010 off the total width?

[LittleBen]

Having that little glass on the belly might make me nervous. Especially since it's bending mainly at the fades, I'd be worried about glass failure there.

Might just take this as a lesson learned and try another.

[adirondacker88]

The bow actually is pretty radically reflexed when unstrung and so working at more than just the fades. Also I meant to say I would take 0.007 + or - off the thickness of the backing glass not width.