Couple of questions about limb stacks

[bornofmud]

Hey, just a couple of questions I was wondering about.

1) I've read that you want to aim for your glass thickness to be 20-25% of the total stack thickness.  Has anyone tried more glass or more wood?  In the 20-25% range, should I aim for being closer to 20% or 25%? Any noticeable difference, or are you pretty safe in that range?

2) Would using say a .04 glass on the back, and a .05 on the belly have the same effect on the bow as trapping the limbs?  Or is it the trapezoidal shape of the limb that gives the limb more stability?

Thanks!!

[jsweka]

1) I have violated the 20-25% rule and not had any ill effects (down to 17% on one Hill style longbow).  At it's draw weight it shoots comparably to one that was 20% glass.

2)  Not sure.  Never tried that, but it might if you're comparing it to a bow trapped towards the back.

[LittleBen]

2) It woulf be similar, but it's kind of akin to user thinner bamboo on a backed bow vs trapping the bamboo ... thinning the bamboo has very little effect compared to trapping.

with the glass, since the surface of the belly and surface of the back do the most compression and tension work, respectively, adding glass from .040" to .050" below the surface whould have fairly little effect. It's too close to the neutral plane to matter that much I;d imagine.

[onemississipp]

1) most recurves would violate that percentage. With glass being close to 50 - 60%.

[Swissbow]

IMHO trapping the limbs towards the back will not give more stability. I think of it more as a way to remove material/mass from the limbs without compromising stability to much.

The 20-25% rule is for longbows. For recurves the ratio glass/wood is more like 40-50%.

In general I try to stay on the lower end of the range because with tapered lams the ratio will increase towards the tips. I don't want to have to much glass at the tips since it's heavier than wood.
__________
Andy

[bornofmud]

Nice, thanks for the answers everybody!

[LittleBen]

Maybe someone needs to make some tapered glass ... although I guess you'd need a ridiculously small taper like .00025 - .0005" or something ...