Spine?

[Hawkdancer]

OK - 26" shaft with 2# weight bends x distance.  Why a complicated formula to figure out the spine?
If all the shafts in a bunch bend the same distance, the spine should be the same.  As long as they pretty close together, who cares!  Of course, I have not been a persistent archer over the last 60-65 years, and didn't own a set of matched arrows until I got my first bow(by luck), but I haven't made very many arrows from scratch, either!  Maybe I am overthinking this thing.  Assuming the same wood of course.
Hawkdancer

[loon]

OK - 26" shaft with 2# weight bends x distance.  Why a complicated formula to figure out the spine?
If all the shafts in a bunch bend the same distance, the spine should be the same.  As long as they pretty close together, who cares!  Of course, I have not been a persistent archer over the last 60-65 years, and didn't own a set of matched arrows until I got my first bow(by luck), but I haven't made very many arrows from scratch, either!  Maybe I am overthinking this thing.  Assuming the same wood of course.
Hawkdancer

I guess if you have a 23" draw and 24" arrows for a 50# bow you could find shafts with a (28-24)*5 = 20# less than 50#? so 30# spine? and they should be more or less in the ballpark you'd want. and to find such a spine with the short shafts you'd need the formula..

[Pat B]

The AMO standard for measuring arrow shafts is to place the arrow on uprights set 26" apart, hang a 2# weight in the center and measure the deflection. This is for a 28" finished arrow with a 125gr point. For arrows more than 28" subtract 5# per inch over 28" or and for less than 28" add 5# per inch under 28". For points more than 125gr subtract 5# of spine per 25gr over 125gr and for points weighing less than 125gr add 5# for each 25gr under the 125gr. All my arrows are cut to 30" so I can easily measure their spine with the formular above.
 If you have an shorter arrow that flies well just measure the deflection and match your other arrows to that. That should work for you.
Also, with cane and hardwood shoot arrows with natural taper you can subtract about 10# of spine weight for that natural taper.

[DC]

Deflection is really as far as you have to go. The formula was just invented to convert it to pounds so Joe Average could match them to his bow. Eastons new system eliminates that. Although for some strange reason they went with 28" and 1.96 lbs or something. If you've noticed their arrows are numbered 200,300,400,500 etc. That's deflection with their system. A lady at the range shoots a 25# bow and she shoots Easton 1000's. They look like knitting needles with fletching. They match her bow and they fly like darts.