Spine Testing Help

[Ground Hunter]

Ok, I must be missing something here.  Bought a new ACE spine tester, the deluxe one.  Tested some known arrows and they are all coming up about 5# short from what my records say they were bought.  Now most of these are tapered shafts.  For example: a known 85-90 tapered shaft is now measuring 80 -85???  What's up here? Operator error?  Thank you in advance!

[Lefty]

Are you spinning the shaft to checking them on more than one place?  There is usually a stiffer side.  If you have an aluminum shaft with known deflection you can double check the calibration of your spine tester.

[ChuckC]

There have been discussions recently.  Could be differences in the tester or it could be that your arrows lost moisture or gained moisture and temporarily changed spine.

[TOEJAMMER]

I know that some suppliers of wood shafts measure the spine before they put the 10 inch taper on and thus end up about 5 pounds less than stated.

[Orion]

All of the above. I'd add one more. You don't always get what you order.  

Unfortunately, your spine tester reports the findings with a scale arm.  Would be nice to measure the actual deflection, on your "known" shafts as well.  You don't really know which, if either, is correct.

[Ground Hunter]

Thanks all.  I've checked it with both aluminum and carbon. They check good.  I just have no confidence in wood.  I'm starting to think the taper is the answer?
What happened is I got about 10dz shafts about 5 years ago.  From 50-55 to 95-100.  The darn rubber bands holding the bundles together broke over time and now their all mixed up!  Trying to sort things out.

[slowbowjoe]

Yes, the taper will have the effect of lowering the spine some. Folks at Surewood told me they figure by 2-3lbs, if I remember correctly.

[Orion]

GH:  So are you saying you tested the spine tester on aluminums and carbons, and it's accurate on those?  If so, it's also accurate on your woodies.  But, as Chuck and TJ point out, humidity and or tapering can change the spine on woodies over time.

Of course, the ACE spine tester is set up to test wood arrows.  It  uses a 2# weight with the arrow suspended on two posts 26 inches apart.  Spine measurement on carbon arrows, done the Easton way, uses a 1.94.# weight at 28 inches.  They yield different results.

A 50# spine deflection using the 2# weight a6 26 inches is .52. A .52 deflection using the 1.94# weight at 28 inches is a 61# spine.  Perhaps that accounts for the differences you're finding..

[Ground Hunter]

Orion, its set for AMO.  It can be set for either.  I think the combination of old shafts and taper likely account for the differences.  It does also have a learning curve when it comes to woodies.  In the long run, the bow decides.  At least I can get them sorted into reasonable batches....   Thank you all.