Spine Tester Readings

[Sherwood Poacher]

Help! Built a spine tester with a dial indicator and am getting readings that don't match that of the chart. The uprights are 26" apart and I have a 2# weight that I checked and it is 2#'s. Don't know what I'm doing wrong, maybe the uprights should be 28" apart?? Would appreciate any help from anyone.........

[Cupcake]

It could be that the spring in the dial gauge is changing the force that the weight is applying.  The dial gauge I tested had about 1/4 pound of spring force at .400" deflection so I decided not to use a dial gauge.

[Cupcake]

Sherwood, another thing to consider,
If you are trying to verify your tester using carbon or aluminum shafts they will not read like the chart.  Those shafts are measured on 28" span and 1.94lb. weight, not the 26" and 2.0lbs. your tester is designed for.  The deflection on your system should be .825 times the chart deflection.

I have a paper I wrote describing the differences and deriving the .825 translation factor if you are interested.
Kevin

[laughing turtle]

I second cupcake's opinion. I built the same setup and never could get accurate readings, i think it is the spring in the dial indicator.

[Flyrite]

Simply remove spring pressure by pulling dial indicator rod away from arrow and slowly bring it back into contact.

[Sherwood Poacher]

Cupcake,
I am using cedar shafts, though I do have a few 2117's from my old compound days. Somewhere I read to remove the spring in the dial indicator and go from there. I'll give that a try and see what happens. Can't understand....it was so easy to build ....only to run into problems like this........

[Art B]

Look around for one of those really cheap dial indicators made in China. I know, I know, little more than junk, but perfect for this application. It's spring is really weak compared to good ones.

You can try this, worked really well on the one I help build for my buddy. Take a lead conical bullet and fit on top of the depression pin to help lighten up its spring. Just work with the bullet's weight until you can lay a shaft from end post to end post and the the shaft's weight alone will depress the pin.


ART B

[Sherwood Poacher]

Art B,
That is what I bought from Harbor Freight, it cost just $10.

[Art B]

You might try taking the back plate off and study the inner workings. May be able to re-work the depression spring or something. But that lead cap I mentioned on the pin may work for you. All I had to do to mine was add a wood cap to the pin. Mostly for a larger contact surface.

If you're just making this tester for self use then your readings can vary somewhat. I'm sure mine's not exact. But I have checked many marked purchased shafts and the readings have all been within the prescribed spine range.

There's more you can do with this type tester then just get your spine reading. Like checking for straightness (aiding in straightening), locating the crooked side, and aligning broadheads (I use roller bearings on the end post).

ART B

ART B

[Sherwood Poacher]

Art B.........Took the back off the indicator and unscrewed the spring.I then tested a dozen arrows that I made up from 70# shafts. The results were that all of the shafts were within the readings .362 to .375....the 70# range. So that was the problem.... Thanks.

Thanks to all others for their help.

The Sherwood Poacher

[Boneyard Bowhunter]

I made one and it checks out great with wood shafts.
The amount of resistance from the spring in the dial indicator doesn't amount to any difference. Make sure you adjust to zero for each shaft.

[aromakr]

You are going to find some variation is wood shaft spines from various suppliers, for a number of reasons. usually operator error, not rotating the grain properly, not zeroing the tester properly, not reading it properly and the biggest mistake, transposing the numbers read. Spining shafts has to be one of the most boring jobs in the world, its very easy to start day dreaming, that's when the errors begin, I know I've spines many thousand shafts. That's one of the reasons I've color coded my tester, all you have to do is see the color and place in the same colored bin
Bob

[Shinken]

Thanks for a great tip Bob!

Shoot straight, Shinken

[Art B]

That's the great thing about making your own spine tester and making your own arrows shafts also. You can cut out the suppliers and their variations. Personally, I got tired of having to buy two dz shafts just to make up a dz arrows. For my purposes, it makes no difference if my tester reads one thing and someone else's tester reads something else. Just looking for that right reading for consistency within a set. And within a given set I color code each individual arrow. Wood arrows comes in sets of ones!

ART B