Spine tester questions

[BoltBows]

Hi guys, i'm going to make a spine tester and found some information about them, i still have some questions and i hope you guys can help me out here.

I'd like to make an adjustable tester so i can spine shafts with different lengths. I found this old topic where ''Waterlogged'' described how to make such a thing. I'd like to build one because im not sure how accurate the 5# per 1'' rule is. And i'd like to know what the spine is of short arrows i've barreled/tapered!
Here's the old topic:
http://www.primitivearcher.com/smf/index.php/topic,4589.0.html

''Waterlogged'' described how you could spine a 32'' shaft simply by plugging 2 nails both 16'' from the centre in the wooden board and measure the deflection etc. However if im right the standard spine tester measures the deflection while the shaft lays on two nails both 13'' from the centre = 26'' to measure the spine of 28'' shaft.
So i'd say; to measure a 32'' shaft, you should put the shaft on two nails both 15'' from the centre! And when measuring a 24'' shaft create a total distance of 22''. You guys agree?
Therefore I'd say the standard formula:                     26
                                                                         ----------------------
                                                 inches of deflection = lbs of spine (for a 28'' shaft)
for example changes into:                             
                                               30
                                 ---------------------------
               inches of deflection = lbs of spine for a 32'' shaft.

I dont know if the formula simply could be changed like that and still 'work.'
I hope it does! keeps things simple.

Cheers,

Rapidfire

[chessieboy]

Just use the plans for the 26" space.  Then you suptract 5 lbs for every inch of extra arrow over 28".  For example and arrow that spines 50 lbs for 28" would be about 30 lbs at 32". 

Bill

[Pat B]

You can measure deflection of an arrow with any set up as long as you are consistant from arrow to arrow. The AMO standard uses uprights that are 26" apart with a 2# weight hung from the center. This will give you the actual spine for a 28" arrow measured in thousandths of an inch deflection.
  Like Bill said, for each inch over 28" you can subtract 5# of spine wieght and for each inch under 28 " add 5#. This spine standard is for use with a 125gr head. The actual spine weight will be the same but the effective spine weight will change with arrow lengthy and/or head weight.

[BoltBows]

Thanks for your replies! the problem was i had short arrows (24'') so i couldnt measure them in on the standard 26'' spine tester. I just wanted to ''make sure'' they wont explode  
They've got a 30 grain heads so that'd increase the spine, but i guess there's no better way of finding out than just shooting them! I'll test them today (if its not raining) and ill post them on the arrows section.
Thanks again,

Jaap