tell me if im crazy... last night i put a white poster board on my basement wall ... two pegs 26" apart..marked a line on the poster board at 13".. laid a shaft across the pegs... the shaft created a perfect shadow on the poster board.. i marked the top of the horizontal shaft on the poster board..this is 0... i made a 1.5" vertical scale on the board that would show the deflection rate.. .500 being 52# etc... so i hang the 2# weight at 13"...the shadow deflects to a point on the (scale) posterboard.. it seems to me i have a pretty accurate reading of deflection.. tell me what ya think...
Sounds like it'll work as long as you're sure of the spine of the sample you used.
Larry
Like any other statistical calculation, you should test plenty of arrows, at least more than a single arrow, for a control group.
IMHO. Great idea though.
:thumbsup:
from what i understand... i can test any shaft you give me... as long as the horizontal shadow hits right on where i marked 0... then it will deflect down on my vertical 1.5" scale when adding the 2 pound weight...im using the amo deflection chart on the rosecity site.. so where ever the top of the shadow line hits... is my deflection rate... its been dead on with all of my arrows of known spine...
Sounds great to me, Steve. As long as the components don't shift in relation to one another, you should be good. Can you post a pic?
Two points I thought of. What happens with different diameter shafts? The shadow will start out other than zero. Would you adjust the back light to change the position of the shadow? Second, How fine are your measurements markings on the poster board? Can you get real close measurements? Otherwise it's a great idea.
i tried it with a 5/16 and a 11/32 shaft... i noticed there is a slight difference.. but by moving the 5/16" shaft a bit..i can get it to line up nicely.. i used a ruler to measure out my markings on the poster board..or you could just tape a ruler to the board... the key is to make sure your horizontal starting point is accurae.. put on your 2# weight.. and just see how far the shadow deflects down...measure that distance to give you your reading..it really appears to work nicely....
awesome jof steve wish I was that smart :banghead:
That's great stuff Steve, way to technical for me. I pick an arrow up and let er fly, if it hit where I was aiming I call it good :biglaugh:
annointed archer...thats the beauty of this.. you could take an arrow that works for you...put it across the two pegs at 26".. put your 2# weight on at 13"..then just measure your deflection...put two marks on your poster board.. you now have your spine..now all you have to do is match any dowel to that measurement or very close and you should be within 5# of the arrow you know that shoots well..right now i'm spining out 25 cent birch dowels to match my sons 44# doublas firs... lets start building arrows!!!!
show us some pics. of this easy spine tester. :thumbsup:
Now you will have to get Jason to give up some of those turkey wings he stumbled on so you can make some real nice Michigan featherd arrows.
i'll try and get some pics tonight...
good one mate
Jeff,, Steve's has turkey wings galore. Steve, I think it will work just fine as long as you don't grow any taller :saywhat:
the line of the shaft shadow is there no matter how tall ya are...unfortunately i think im done growing vertically..but i seem to get wider each year..
ok ..i tried to take pics and its too difficult to show the line of the shadow on a photo... this is very simple to do..make sure you have a light source behind ya...two pegs 26" apart... a white board or paper behind the shaft... make sure your shaft sets stationary on the pegs at 26"..mark a verical line at 13" on the white background behind the shaft....you will hang your 2# weight on the 13" mark..mark the top line of your shaft shadow on the paper..this is 0.. put your weight on the 13" mark and let her hang... again mark the shadow line top of the shaft... the distance between these two points is the amount of your deflection... refer to the amo deflection chart on the rosecity site.. hope this helps..any questions just pm me..
Just a question, but why not use bottom of the shadow line as the beginning of the measuring point. if this is where the support of the arrow is, that shadow should be consistent no matter what size shaft is used. Use that point as O and use your deflection graph or measurement from there?
yep..you could do that too.... i was playing with this last night and made my mark from the top line...the key issue is that the shadow line is even with mark 0...whether top or bottom...it is basically just an easy tool to measure deflection... i have all my measurements premarked now... and from what i can tell ..it is quite accurate... at least accurate enough to put you within 5 pounds on woodies...rwsbow..i think your idea would probably be a better method.. if anyone else has any good ideas.. please toss them in..
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?
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.
Here's an easy way to get precise deflection
http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=040744
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.
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?
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.
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...
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.