A break-down Spine Tester

[Davesea]

My favorite version of a spine tester is the bananas hanging from a shaft on a fence with two nails. Proof that determining arrow spine is not rocket science.

I have wanted to build a break down spine tester that I could pack away in a drawer and use around the house.  My other one is built into my cabinets.  Finally got around to it.

Here is what I came up with. Works great and is accurate to within a couple hundredths of an inch. It also adjusts so that I can test 13-30 lb spines (1-2" deflection) spines by using 2# at a span of 21" which will keep the deflection less than one inch. Wanted to keep it compact. the weight is a 2# scale weight ($5 used online). The alignment shaft on the bottom breaks in half for packing.

Shown here are photos using carbon and aluminum arrows for calibration.

Dave
Seattle

[toomanyknots]

very cool!

[Pat B]

Now, that is cleaver!!!   

[Buckeye Guy]

Looks good !

[Zuma]

Very interesting and well assembled Dave.
I did a search here on the forum for spine tester. Your thread here is the only result.
I get the breakdown part. Would you mind walking us/me through the other parameters?
Like what does the meter read,(psi)? The function of the black lever handle etc.
I understand why spine is important but how do you translate psi at the end of the shaft to the flex of the shaft.
thanks Zuma

[Davesea]

hi Zuma,
the dial indicator is described here
http://en.wikipedia.org/wiki/Indicator_(distance_amplifying_instrument)

The black lever allows quick release and adjustment of the dial indicator.
http://www.leevalley.com/US/hardware/Page.aspx?p=45034&cat=3,43576,61994

once the dial indicator is adjusted to touch the underside of the shaft, hook the two pound weight on top of the shaft and the dial indicator will measure the distance the shaft is deflected by the weight.

does that help?
Dave

[Zuma]

Cool lever and reasonably priced.
The indicator link seems a notch or two off. Maybe you could check it.
Thanks no matter what Dave.
Zuma

[Davesea]

Here is a link to a dial indicator from Harbor Freight.
http://www.harborfreight.com/1-inch-travel-machinists-dial-indicator-623.html

[Gus]

Cool Thread - Design...

Thank You for sharing.

-gus

[Zuma]

Dave that link worked great. Nice economical and stowable set up.
Thank you very much.
Zuma

[SamIAm]

This is really slick.  I'd like to make one but I'm having difficulty in understanding how the meter attaches to the stand.  Is there any way you can clarify that?  Sorry to be so dense.  Thanks.

[Pat B]

Sam, the dial indicator measures the deflection of the shaft in thousandths of an inch with a 2# weight hanging on it and you compare that measurement to a chart that tells you the spine.

[willie]

SamIam
the back of the indicator has an ear that attaches to the camlock from lee valley. The whole assembly rides up and down in the slot you see in the stand. This is how the tester is zeroed.

http://www.leevalley.com/US/hardware/Page.aspx?p=45034&cat=3,43576,61994.

If the arrow is not perfectly straight, or the same as the last arrow tested, then the tester needs to be re-zeroed for each arrow. I bet that someone who spines a lot of arrows can find an quicker way to do the zeroing.

[SamIAm]

Thanks Willie.  I think I'll order the parts to make this....reasonably priced.  When I put my hands on the parts I'm sure it will be clear.  I understand the principle.  You'll have to excuse me, I'm from Missouri.   

[Danzn Bar]

Sam, the dial indicator measures the deflection of the shaft in thousandths of an inch with a 2# weight hanging on it and you compare that measurement to a chart that tells you the spine.

I agree with Pat....
You can also do it backwards if your looking for arrows for a specific bow.  Take 26 and divide it by the pound rating of your bow at your draw length and that equals the deflection of arrow to start with. there is a lot of factors that effects spine, but it's a good start.  eg. for a 52# bow  take 26/52= .500 deflection

SamIam
the back of the indicator has an ear that attaches to the camlock from lee valley. The whole assembly rides up and down in the slot you see in the stand. This is how the tester is zeroed.

http://www.leevalley.com/US/hardware/Page.aspx?p=45034&cat=3,43576,61994.

If the arrow is not perfectly straight, or the same as the last arrow tested, then the tester needs to be re-zeroed for each arrow. I bet that someone who spines a lot of arrows can find an quicker way to do the zeroing.

The way I zero......is if the arrow pushes the plunger down...I turn the dial face to zero and your ready to go. I always set the dial so the arrow touches or just barely depresses it without the weight.