tell me what ya think of my spine tester..

[jacobsladder]

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...

[LAR43]

Sounds like it'll work as long as you're sure of the spine of the sample you used.

Larry

[gwhunter]

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.

[TexMex]

[jacobsladder]

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...

[SCATTERSHOT]

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?

[NY Yankee]

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.

[jacobsladder]

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....

[robslifts]

awesome jof steve  wish I was that smart  

[AnointedArcher]

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  

[jacobsladder]

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!!!!

[JEFF B]

show us some pics. of this easy spine tester.  

[AnointedArcher]

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.

[jacobsladder]

i'll try and get some pics tonight...

[JEFF B]

good one mate

[whitebuffalo]

Jeff,, Steve's has turkey wings galore. Steve, I think it will work just fine as long as you don't grow any taller  

[jacobsladder]

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..

[jacobsladder]

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..

[**DONOTDELETE**]

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?

[jacobsladder]

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..