new spine tester variations

[laughing turtle]

I just completed the spine tester using a dial indicator i found on this site, Hill's design i believe.  I was testing some shafts i bought from 3rivers.  I ordered 60-65# but upon testing with the dial indicator and 2#'s exactly, i am consistently measuring spine groups from 65-70# or .400-.377 inches of deflection(over 100 POC shafts).  My question is this, do the manufactured spine testers that are on the market provide less accuracy?  I have also checked arrows of known spine against my tester and found them to be equally off. I realize that so long as my spine groups are close i will see consistent arrow behavior.  Anyone else built this design and noticed the discrepancy?

[JRY309]

I think I read somewhere that using a dial indicator you have the indicator pushing down on the shaft along with the 2# weight has a slight effect on your reading.Its not much pressure but it is some pressure.When I had a spine tester I just used it for consistent arrow groups then I would bare shaft tune.I might be wrong.

[FJTOYMAN]

Yeah I built an indicator tester. It is a little off. You'll learn to compensate for it.

[draco]

I built a similar spine tester years ago and mine has proven very accurate and compares to an older commercial model of a friends,And it reads off the bottom of the shaft. Yours is probably right. The poplar shafts I got from 3Rivers recently were 5# heavy and cedar shafts I got in the spring were 5# light. Try shafts from the Cedarsmith,he`s great,the shafts are great and they spine right. Also he has a great price on 2nd`s that are almost 1st`s. They make great small game shafts,You will like him; Bob

[Cupcake]

The spring force of the dial indicator could be much more than you would expect.  When I was designing the Spine-O-Meter I rejected the dial indicator becase I measured several ounces of force and that will affect the measurement a lot.

Try pulling the indicator shaft away from the arrow and just touching it to see what reading you get, this will eliminate the spring tension if you hold it and just touch the shaft.

The best way to verify your tester accuracy is with an aluminum shaft - they are very consistant.  If you have an Easton aluminum deflection multiply that number by .825 and that will be the deflection you should measure on a 26" span with 2lbs.  I have verified this method on almost all of the Easton aluminums and it is stone reliable.
Kevin

[DesertDude]

Yep......Knew Kevin would respond....

[aromakr]

The problem is if the Dial indicator is applying too much pressure it would read less poundage and more deflection not more poundage and less deflection!! So I don't think his problem is his tester just the wrong spine shafts. Keep in mind 3 Rivers does not re-spine their shafts they take the word of the manufacture as marked on the box.
Bob

[laughing turtle]

Thanks for all the input.  I believe the shafts from 3rivers were incorrectly marked to begin with as i tested aluminum and the tester is dead on accurate.  I will continue to experiment.