How do you choose your glass thickness?

[beachbowhunter]

Is there a rule of thumb relating the glass thickness to core thickness (ratio) for good performance? I know there are tons of variables, but choosing between the available thicknesses of glass to get to your target stack is not clear to me yet...

I am guessing that thinner is better because the glass is heavier than most core woods. I would probably step up to thicker glass if I had a higher target weight and wanted a "sturdier" limb. Off base?

[Glunt]

I use .040 for everything, It keeps things simple and has worked great on 40# - 60# bows.  Its thick enough so that I can remove a bit if needed to hit weight, and I haven't seen a good case for thicker glass.

[beachbowhunter]

Ok, now you're using logic on me.  :D  That sounds like a pretty reasonable approach.

[bigbob2]

Have seen where glass is between 1/4 and 1/5 of total stack.

[kennym]

I agree with Don and Bob. 20 to 25% is the norm for longbow, maybe thicker on curves.

[jsweka]

What effects are there if you are below 20%?

I ask because I have a bunch of 0.040 glass that I bought from a fellow Trad Ganger last year and was thinking for my next Hill style longbow, I'd need 0.45 total stack.  That puts me at 17.8% with 0.040 glass on both sides.

[kennym]

If you get too thin, and I'm not sure where that starts, you can get some set even in a glass bow.

I did a survey a few years back and most agreed on the 20-25.

I've had one bow take more set,  when I used .002 taper in the limb instead of.003, and maybe the riser wasn't faded out enough.

Only on the bottom limb too, man did that make me shoot high til I did some checkin!

[rmorris]

I started out with .050 glass and that is all I use now because I can hit weight with it. I also only do  longbows so I know nothing about curves.

[jsweka]

Hmmmm....Never gave set a thought.  I guess I could end up with one of those string follow bows some of the Hill followers rave about.

I still get a little set in the straight limb bows I've made even with 0.050 glass (23% of stack thickness).

[kennym]

Yeah, I get a little set on each bow too, if you lay a bow back on the form after several hundred shots, bet every bow has some..  

[Stagmitis]

On my deep core Hill bows I have noticed the following. The back glass is responsible for keeping backset while the compressive nature of the belly glass aids in speed and stability. Since I trap all my bows this alters an even ratio so I always use a thicker belly glass relative to the back.

[jess stuart]

I also use .040 for the weight ranges I build in.  I have used .030 a few times for bows for kids.

[Swissbow]

20 - 25% for a longbow and up to 35% for a recurve.

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Andy

[beachbowhunter]

I think my first set of limbs (TD LB) is right around 25 - 26 % using 0.040 (measured actually 0.038). My target weight is 50 @28. I have to recheck the actual, but I was going for a total stack of 0.300 based on the Binghams chart.

These are terrific "rules of thumb". Thanks guys!