I've built a good deal of Hill style longbows. Last few I've had a good deal of limb set. I've been using relatively thick cores (.470 total stack w/glass) with .040 glass belly and back. Would I be better of with .050 glass to avoid as much set? Does core material matter? I've noticed maple had more set than action bamboo.
This may sound crazy, but I was under the impression glass sandwiches took almost zero set?
I was under that same impression Chris! SO maybe we're both crazy. Someone fill us in here.
I've had some take very very little but one recently that took about 1" on me. And it was only one limb. It had .040 glass but I've had some w/ .040 glass not do it at all. Moisture content and glass thickness come to mind as culprits but just want to hear what some guys have to say.
Most glass lam bows take a little set but it is minuscule. Mine generally take under 1/8". High core to glass ratio will cause more set but more is relative. Anything over 1/4" is something to worry about. In this case 1" on one limb is indicative of another problem. I would suspect lam slippage. Is the handle still centered in the bow? Could the hose or clamps on one side have relaxed before the bow was done cooking? We're you able to tiller it ok? I believe something else is going on as the any set I have seen has been uniform.
Bonner
Easier to notice on a strait bow, but all bows do that to an extent. I've laid d/r bows back on form and had 1/4" .
Some guys call it springback, happens when you take a d/r off the form. You are making the wood bend differently that it grew there.
You bend wood enough and even sammiched in glass, it will lose a little memory .
1" on only 1 limb is troublesome. Check distance to string every 6" from fades out and see if anything jumps out at ya.
I am slowly coming to the conclusion that glass / core ratio plays a bigger part than we might thing.When the ratio is well within the theoretical 20%- 25% I get minimal 'set' or string follow but push it to limit of that ratio and limbs get a little more 'set'. Glass will revert to its original plane whereas wood is easily induced to curvature. Increase the ratio and the core might overpower the glass, or conversely the glass is too 'weak' to resist the core's need to bend.
Different wood cores have different compression and tensions properties. The pairing of some of those woods can add to the amount of compression on the belly lams and will take more set than others as the lams are worked in. Once the wood is compressed beyond what it can withstand it will become weakened and take a set.
In my hybrids I have observed 4-5 lams have no stringback off my form but 2-3 do. I figure this is impart to the ratio of glue to wood/grass in the core being offset by the extra glue and the very thins lams soaking the glue up.
As I use 4 lams in nearly all my bows I can make direct comparisons. Totally agree with stickmonkey that different woods will give different values, but have noticed differences in woods of similar values and the only difference was Stack/ glass ratio.All my straight laid HH style will have small degree of follow but when the ratio is at the limit instead of .25'' it may be .75''
I get similar results to Bob in my Hill styles too. More set when using 0.040 glass compared to 0.050 glass.