Spine tester results

[kat]

I have a question about some spine tester results I am getting.
First of all; I made a spine tester by using Jim Hill's plans. The parts were all made from aluminum, and machined on a CNC mill.
My arrow supports are 26" apart, and my 1" travel indicator is in the middle of this span.
I am using a 2.00 pound weight that is resting on the arrow, which in turn is resting on the flat point of the indicator.
I am sure of my measurements, and the 2.00 pound weight.
When checking carbon express 4560 arrows, I am getting .330" of deflection, both on new and used arrows. The deflection seems very consistent when
I rotate the arrow, and when I switch arrows.
This would translate to about 79#'s of spine. The specs. on these arrows should be .403" of deflection and about 65#'s of spine.
Any thoughts on the disparity in readings?
Thanks,
Ken

[Looper]

I think you're supposed to use 28" and 1.94#s for carbons.

[SlowBowinMO]

X2

Carbons and aluminums are checked on 28" centers with a 1.94#.  However if I convert your wood spine reading at 26" to carbon, about 78# is a .400.  Your CE arrows are right on.  

[portugeejn]

There is a chart out there somewhere on the net that converts aluminum spine to equivalent wood spine or vise versa. I used it to build/test my spine tester. Google search?

RonpP

[Kelly]

Your readings are correct at 26".

The specs of .403 are for 28" centers, which is where carbons and aluminums are measured.

Do you have any aluminums to use to check their spine to help verify that your spine testor is calibrated correctly, which from the sounds of your description it is.

The two most critical ingedients are 26" apart for the posts and the 2# weight/indicator is in the exact center between your posts which you say it is. What are you using for a scale-dial indicator?

[kat]

Thanks all for the help.
My scale is good to .1 g.

I added a new set of holes to measure at 28" between supports, and changed the weight to 1.94#'s. The numbers are much better now.

I am mostly working with carbons, so this eliminates any math errors.

[Kelly]

"My scale is good to .1g"

You mean your scale is good to .001 thousands, correct?

By scale I meant what device are you using to measure deflection in thousands?

[drewsbow]

Ken : I built mine and used alum arrows of known spine to calibrate with three different spines.

[stringstretcher]

Something that will help you convert the ASTM spine to AMO.  If you take the ASTM spine rateing and multiply it by .825, it will give you the AMO spine.  IE:.403X.825=.332475 or rounded off .332 AMO deflection.  So your spine tester is correct.

[SAVIOUR68]

Kelly I have made the same hill style tester and I used a 13.00 dial indicator from harbor freight which measures in .001 up to 1.00 in. This tester works fantastic and have about 20.00 in the whole set up.

[kat]

Kelly,
I took scale to mean weight scale.
My indicator is a 1" travel indicator that measures in .001" increments.
Thanks again,
I am all set now.

[Kelly]

Any pictures of what this spine tester looks like?

Thanks

[kat]

 
 
Here it is at 28" between supports. I added lead pellets in the cup atop the 3/4" shaft to make the 2.00 lb. weight

[kat]

Here it is showing the supports.

 

[Reaper TN]

Good lookin' tester you built Ken!

[kat]

Thanks Benny.  I think it will work just fine.

[Kelly]

Originally posted by kat:
 
 
 
Here it is at 28" between supports. I added lead pellets in the cup atop the 3/4" shaft to make the 2.00 lb. weight

Yes awesome job on building an effective spine tester. Just wish I had machine capibilities to do work like this.

[drewsbow]

very nice set up Ken