ATA or ASTM spine?

[DC]

There are the two standards for spine. ATA is 26" centers and 2# and ASTM is 28" centers and 1.94#. I've read that ATM is to be used for wood and ASTM is to be used for aluminum and carbon. That said, I was using some bamboo shafts(more wood than carbon) from Tiger on Amazon that were spined at 45-50#. But it said they were hand spined at 28"(ASTM?). When I tested them on my ATA tester they came in at 60-65#. I did some searching and found a thread that said the conversion was 80% from ATSM to ATA and 125% the other way. 80% of 60# is 48# so it does fit. How does anyone make any sense of all this? How can the two different organisations say that their method will match an arrow to a bow when they seem so far apart? I realise that the final straw is testing but if I want to order 100 or so shafts I would rather be a bit closer than that.

[Pat B]

I've only use the spine tester and chart that I got off the internet from JamesHillSpineTester dot Com.

[mullet]

I think you could build one using any size weight and distance apart as long as you were consistant and had arrows that you knew the weight of as a starting point.

[bjrogg]

I really don't exactly know answer DC. But I use 26" with 2 lbs. of wieght. Then I just divide 26" by the deflection measurement. That tells arrow shafts spine but it still changes with length of arrow and point wieght for actual arrow spine. For my bow about 67 lb spine with 31" long arrow and 125 grain point seems to bare shaft just right. I took me awhile to come up with those spec's but I think in theory I should be able to replicate. To match wieght I remove material with file usually from front fat part of shoot shaft. I really just started doing this and I'm sure there are guys that know way more than myself but I made 2 matched arrows as close as I could with my equipment and I'm suprised how much better they shoot. Good luck pappy explained bare shaft testing real nice in Osage outlaws arrow build along.

[DC]

I've done a little looking and it appears that I'm a little out in left field. ATA coverts deflection into pounds so you get a "40# arrow". ASTM doesn't  do that, they use the deflection as the spine measurement so you get a "500 arrow". One does use 26" centers and the other uses 28" so you still can't compare them directly. I stole this quote from "Spineometers" site

"What does all of this mean? It is very simple: if you know the spine of a carbon shaft is 500,
which means .500 inches deflection, multiply .500 by .825 and the result is .413 inches
deflection in the ATA method. The ATA spine is simply 26 inches divided by .413 inches
deflection to get 63 pounds spine.
Conversely, suppose we have a wooden arrow of 95 pounds spine and we want to determine
what carbon or aluminum deflection is equivalent. Start by dividing 26 inches by 95 pounds to
get an ATA deflection of .274 inches. Next divide this result by .825 to get .332; the closest
carbon shaft is a 340. Three decimal places for these calculations is sufficient accuracy."


What does this mean as far as me buying bamboo shafts of the internet. Order a dozen first and measure the spine  and then order the 100. Buyer beware.

[bjrogg]

That sounds right to me DC. Actual finished arrow spine will still be changed by length of arrow and wieght of tip. The important part is to come up with combination that shoots good bare shaft. You might still be able to do that with your shafts. If you shoot bare shaft and arrow flies cross ways knock to the left spine is to light, you can shorten arrow a little at a time till it flies straight. You could also try lighter point. If arrow flies cross ways knock to right spine to heavy, either file or sand some material off middle of shaft or try heavier point. Also shoot arrow knocked both ways on bow and keep track of which way it flies better you don't want to go through all this and then fletch it backwards. When you find right combination then that shaft spine, arrow length, and tip wieght should be what you want to replicate. This still doesn't match wieght but it will let you know what spine shafts your bow likes. It takes a little time but it's not that difficult and makes a bigger difference than anything else I've tried so far good luck hope that helps.