How to re-visit on spine testers

[Lombard]

Found this Spine Tester thread in the how to's and build alongs. http://www.primitivearcher.com/smf/index.php/topic,4589.0.html  I made the pointer as describes in the last PA issue, that highlighted a build for a spine tester. I liked this spine tester, because it is scalable to different arrow lengths. All I need now is to make the two pound weight, do some sanding, and put a finish on it.

This should make grouping the arrows I build easier, as what I had before is just a couple pegs in my tillering station, a one pound dumbbell, and a pencil mark etched in the plywood, to give instructions on arrows that match my go to bow.

This is as easy a build as one can do. The longest step for me was getting my printer to work, to print the scale. I am not so computer savvy as I would like to be.

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[aero86]

good job!  will make consistent groups of arrows for ya!

[Pat B]

Nice tester. Should be easy to read.
  The standard for a spine tester is to have the uprights at 26" apart and it is for testing a 28" arrow. For any arrows over 28" subtract 5# of spine weight per inch and add 5# of spine weight per inch for any arrow less than 28".  A different spread between the uprights will give you inaccurate readings.

[Lombard]

Thanks guys. Pat that clears up something for me. I was trying not to get hung up on the ratios, but realized that a two pound weight on a shaft twenty six inches would reflect a different ratio than the same weight on a thirty two inch shaft. The movable pegs will easily allow me to pin them at 26 inches, and that is easy math. Should have nicely grouped arrows in no time.

[natty]

i know this sounds stupid, but were does the weight go, also how does it attach .

[Lombard]

Not stupid Natty, if we were born with all the knowledge we needed to live, we would have been born reptiles. Doctored photo should give clarification. As the arrow flexes under the weight, the needle reflects the amount of deflection on the chart. It will need to be tweaked to get it dead on accurate, but you can see how it will allow you to group arrows by spine.

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[Orkraider]

I have to say, that's about the simplest and slickest looking spine tester I've seen so far.

Now, Just so I know, the rests or nails are normally 26" apart, for a 28" arrow, and the weight is 2 pounds, yeah? 

can you simply measure the spine in inches of deflection if you haven't put the needle and chart on?

And is it the case that somewhere there's something that says what the spine is in weight for amount of deflection in inches?

I'm assuming that deflection is the right word.

[Lombard]

Orkraider, in the last issue of PA there is a chart that has a spine chart and gives the numbers in deflection values. Pat gives clarification on the standard for twenty six inches, in his post above.           

[Orkraider]

sweet, I"m going to have to look for that.  I"m hitting the book store this afternoon, hopefully they have that in their back issue stash. 

I did find a formula that says, for spine in pounds, divide 26  by deflection in inches.
 
So, if I have a shaft that deflects .5 ", that would be 52 pounds.