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Help-Tiny very simple spine tester

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wolfsire:
I have downloaded instructions for an adjustable spine tester that seem really good, but I do not want to build it right now with the limited time I have.  Instead, I’m looking for something really simple and fast.

I have a small bow 35lb at 20” and want small arrows (this time), so I’m thinking 30lb at 21”.  If I put 2 nails 20” apart, drawing a straight line between them, and measure from the mid point the downward deflection with a 1lbs weight, what distance will get me 35lbs?  What about 2 lbs?  I think 35lbs that would be the weight I want given that the extra inch will reduce my spine by 5lbs.  2lbs would be more accurate, but 1 would be safer on the light arrows.

I have yet to find a formula and I do not want to build and use a meter that are are based on forumula.  I want to draw a second line to mark the correct deflection and eyeball it.

Thanks in advance for your help.

knightd:
Well to just use it for this bow and arrow set.. I would say find a shaft that shoots well off the bow and use the system you suggested and hang what ever weight you want on it mark it. then just use it as your reference point for the rest..

Pat B:
With the nails 26" apart, a 2# weight and reference arrows, David's method is almost as good as any. You can use it for the arrows for the kids bow but also any bows you shoot.    Pat

wolfsire:
Thank you gentlemen, your comments are helpful, but still leave me in need of more. 

Regarding copying a shaft that shoots well, I will do that, but after I have a working spine to begin with.  The initial problem with this method is that I am almost a completely incompetent archer.  Right now I am all over the place, so I cannot find a shaft that shoots well.  Once I have some that I know are the same in the ball park, I can work on my from, develop some consistency, fine tune that by judging spine up or down based on missing left v. right, then coping as you suggest the most appropriate spine. 

Regarding, 26" with 2lbs, I’m happy to work with that if I can.  But I do not quite now how.  Jim Hills' table for that says to get a 26" arrow to spine at 35lbs with a 2lb weight, you want a deflection of .743.  If that number is not a distance in inches, then I do not know what it is.  I could make an arrow 26" and put 2 lbs on it.  That will give me both a distance and an arc.  I might be able to do something with that, but I am not sure what.

If we could add 5 inches to a 21” arrow spined at 35, with 5lbs per inch, then the longer arrow should then spine at 10lbs.  I do not know what to do with that.  Hill’s table does not go that low.  I could not spine at 26” arrow at 10lbs then cut it down to 21”.

If length/deflection=spine then 20”/deflection=35lbs gives me deflection= .58 or 37/64.  I can measure that if it is in inches.  But I do not know if it is.  Is it only good for 2 lbs?  If I use 1lbs would that be 18.5/64"?

Or is this formula only good for 26” and 2lbs and 5lbs/1” only as estimate that works on the margins?

Thanks again.

Pat B:
Modern arrows are  spined using a 28" arrow with a 125gr point. The spine tester's uprights are spaced 26" apart. For each inch under 28" you can add 5# of spine weight. My spine tester is my version of James Hill's tester with a dial indicator.
 Check out  http://www.jamesmhill.com/spine_tester.html.  He has all the info you need to make one for very little money.
   With kids arrows I start with a small shaft(5/16) and cut it longer than the draw(sometimes as much as 28") and reduce the length until I find what shoots best.
       Pat

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