spine testing

[mikieg]

i am making a spine testing device. mine will read shaft deflection with a dial caliper in .001's. where can i find a chart that shows lets say "if  a shaft bends .56 then that is considered to be a 50-55# spined shaft". basically i want to convert shaft deflection in decimal form measurement to spine weight in pound format. hope i am saying that right, cause i am startin to confuse myself!

[Pruneemac]

google

[AkDan]

you could also purchase aluminum or carbon with known deflections to calibrate yours...

[mikieg]

yup, already did. the formula is the distance between center pins devided by deflection in inches. so if my tester uses 26 inches on center between pins, a two pound weight, and my dial indicator reads .26 of deflection, the formula should look like this... 26/.26 = 100 pounds.
so it seems that folks are trying to find a dozen woodies that will spine up the same. so here is a thought. we know the static spine changes as we spin the shaft in the tester. grain vertical is stiffer than grain horizontal. so if we have a dozen shafts that are close in natural spine weight to what we want, cant we spin them till they deflect the same dial reading as the weakest in the group. and as they dial up to what we want mark the shafts and install the nocks according to marks. so we are fine tuning our spines to be the exact same within this group my "clocking" our nock/string/shaft grain position. shouldn't be too hard to do, there are lots of arrows flyin around where the builder never considered grain orientation when he installed the nocks!

[Don Stokes]

Mikieg, don't take any chances by changing the wood orientation! If you've ever seen what a broken shaft can do to your hand, you would know why! You could get away with it with some species, but with others it could be dangerous. I wouldn't buy arrows from any builder who didn't consider grain orientation.

I'll e-mail you a copy of my Superceder spine chart. It's in deflection, but the self bow column matches deflection to pounds, and is very close to the traditional AMO scale. The deflection number in the self bow column is the high end of the range listed in the bow draw weight column. The chart was created by bare-shaft matching hundreds of archers with bows of different kinds.

[mikieg]

thanks don.