tell me what ya think of my spine tester..

[Steve Kendrot]

A carpenter square would held to the bottom of the deflected arrow would be less vulnerable to relative changes to in the light source as well?

[Jim now in Kentucky]

spiine  gauges  usually  have  a way to multiply the  movement so you can more  accurately read the deflection.  That's why they have a  long  pointer  and  a  large scale.

Your method may well  be  accurate enough for  anyone's needs.

I use  a setup  with a  dial  indicator.  It  is  more accurate than I need.

[poekoelan]

Here's an easy way to get precise deflection

 http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=040744

[Talondale]

The problem I have with this method, if I understand it correctly, is that the arrow will change it's relation to the source of light as it bends, this will cause the shadow to lengthen or shorten depending on the direction of the source of light. (Think evening shadows vs. noon shadow)  So... it sounds like you are using a constant deflection measurement ".500 being 52# etc... "  This won't work exactly because your shadow is moving in relation to the light.  It should be good enough for relative measurement, ie. a bunch of same size arrows compared to a known good arrow, but won't work based on a standard graduated scale of measurement.  Your grid/scale marks are a constant but the shadow will be more of a gradient change.  On a graph your scale would be a straight diagonal line but the shadow would be a curve.  I'm not sure it would be enough to make a difference but it's something to consider.

[jacobsladder]

im pretty sure i get what your saying...i've got this taped up on my basement wall with a stationary ceiling light behind me... so far i have seen no difference in deflection at different times with the same shaft... and every time i set a shaft across the pegs...the shadow line is hitting right at my 0 mark...now if i change any of these components..including my light source behind me..i'm sure that it would throw things off... but if all the components stay the same... the light source, the pegs at 26". the 13" mark,the 2# weight, and my shadow line is deflecting from the 0 mark...i should have a good measurement of deflection shouldnt I?

[Talondale]

What I'm saying is that as the arrow bends down it's relation to the light is changing too.  This is going to change where the shadow hits, in addition to the change caused by the deflection.  The only way to be consistent is to have the light move with the arrow so that it is shining from the same angle regardless of where the arrow is.  The further from the light the arrow moves the longer the shadow.  Take a flashlight and shine it on the arrow and then move the flashlight up and down.  You will see the shadow changes size and shape.  That's essentially what you're doing but the arrow is moving not the light.  So the shadow is not staying constant in size and shape so it isn't a very accurate source of measurement.  Whether it's enough change to make a noticeable difference in results I don't know.

EDIT:  It will be "accurate" relative to itself. That's why you get the same result with the same size arrow everytime.  But that can't be extrapolated to other arrows or enable you to use any kind of gradient to determine other spines.  So you can take a known size arrow with known spine and determine if other arrows of same size are less than/equal to/or greater than the known spine but that's about it.  If you take a series of known spines of the same size you may be able to create a scale but you'll find the degree of change in distance marked is not consistent (it should grow I think)  So, for example you have known arrows of 20#, 30#, 40# 50# and mark the deflection of each.  The distance between the 20# and 30# may be, say .5" and the distance between 30# and 40# may be .75" but the distance from 40# to 50# may be 1.5" because the arrow is starting to get a great enough angle from the light that shadow distortion is really starting to show. (the farther from the light source the greater the effect on the shadow) That's what I mean by the graph being a curve rather than a straight line.  This scale may not work with a different diameter arrow so you have to have a seperate set of knowns.

So you've got two variables: the angle in relation to light changes which affects where the shadow is thrown, and the size and shape of the shadow changes.

[jacobsladder]

gotcha..now i see what your saying and that is a good point... i recieved a half dozen shafts from scattershot that he had spined and written a number on... i was only off by 1# on all 6.. so i'll check and see what instrument he is using.. this may be a good enough way to group arrows and compare to one you have that is shooting well...and if i can stay withing 5# on my woodies i'm pretty comfortable with that...

[SCATTERSHOT]

I think your method is as good as any, and better than most. As long as you're in the ballpark, and your arrows are flying well, that's all that amtters. You can overthink this stuff. It's not rocket science.

For what it's worth, Howard Hill didn't even spine his arrows. He shot several dozen into a sandbank and grouped them by where they hit in the target.