Main Discussion Area > Arrows
Spine Testers
agd68:
shafts are spined for a 28" shaft with the posts of the tester 26" apart, then you add or subtract 5lbs for every inch greater or lower than 28 " of shaft lenght So would'nt increasing / decreasing the distance between the posts do the samthing as adding or subracting to compensate for length ?
CraigMBeckett:
Hi agd68,
The answer to your question is no, the central deflection of a simply supported a beam subject to a load at its centre is defined by the formula y = (WL3/48EI) the 3 is meant to indicate the cube of L that is L x L x L where L is the length between supports. As the equation is based on the cube of the length between supports simply moving the support to increase or decrease the span length will not give you the same answer as that obtained using the standard AMO method plus modifiers.
You could of course use the old GNAS (British) method and tables these were meant for use with ELB's. In this method the arrow is supported just behind the pile and in front of the nock and a weight of 1.5 lb is applied. The deflection (in 1/100 parts of an inch) gives the GNAS spine unit and the corresponding spine comes from a table as below:
GNAS Unit Spine lbs
81 30
61 40
49 50
40 60
35 70
Don't seem to be able to find out much more about the GNAS system it no longer seems to be used and has not really made it onto the internet I have calculated out the curve and extended the table as below.
GNAS Unit Spine lbs
25 100
16.5 150
Craig.
agd68:
Thanks that is very helpful.
Asafan:
Here my scale for 26 inches and 2 lb of cargo. It is convenient to calibrate a tester any tubes. Sorry for literacy :) . Added full size pic.
[attachment deleted by admin]
jeff halfrack:
I'm nobody, but could this be saved in the read only thread,,,after it runs awhile??? this is good stuff thanks JEFFW
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