Spine differences ?

[Stick Bender]

Why do some arrow suppliers rate there spines at 26 in. & Some at 28 in. ?  & then some don't list how they spine test !

[loon]

http://www.primitivearcher.com/smf/index.php/topic,60156.0.html

Wood arrow makers should use the AMO standard (2lb, 26")
apparently a lot of the carbon arrow makers use their own random, non standard spine measurements. Everyone should just use ASTM or AMO.

[TSA]

this conversion table should help.
wood are measured at 26" with a #2 weight
carbon at 28" with a 1.94# weight!

[TSA]

Quote:
ATA, AMO, and ASTM
ATA (AMO) is the Archery Trade Association, formerly the Archery Manufacturers and Merchants Organisation. When they measure the arrow spine, they record the deflection in thousandths of an inch. An arrow is attached to two supports, 26 inches apart, and pressed in the middle with a weight of 2 pounds (907 grams). A deflection in the arrow of 0.4 inches gives an arrow spine of 400. The arrow spines of wooden arrows are measured according to the ATA system.

ASTM is the American Society for Testing and Materials. In their Test Nr. F2031-05, they record the deflection in thousandths of an inch. In this test, an arrow is attached to two supports, 28 inches apart, and pressed in the middle with a weight of 1.94 pounds (880 grams). The weight is smaller, but the distance between the supports is greater, which should give a similar deflection. Arrow spines of carbon fiber and aluminum shafts are specified according to the “modern” ASTM standard.

ATA and ASTM values can be converted as follows: ATA / 0.825 = ASTM, therefore ASTM*0.825 = ATA

Example: A carbon fiber shaft has an arrow spine of 500 according to ASTM (28″ distance, 1.94 pounds). 500*0.825 = 413 spine according to ATA (26″ distance, 2 pounds).

In other words, an ATA shaft will always be stiffer than an ASTM shaft with the same “number”. Carbon fiber arrows measured with an ATA device will appear slightly “softer” than the manufacturer listed value.

[Stick Bender]

I should have stated that I was referencing wood arrows only and the deferences in spine measurment but on the topic you rarly ever see any data on alinimum arrows any more , thats all I shoot threw my FG bows  when I rarly shoot them these days carbon arrows never stood up to stump shooting well for me , but ceder arrows only faired slightly better but these Douglas Fir arrows are tuff as nails with the exception I found some 30 year old 55-60s cedar  arrows that I forgot about that are solid & there heavier mass then current cedars well a little off topic but interesting subject !

[TSA]

i hear ya mate!
thats the problem with POC  sadly, as great an arrow wood as it is, many people are being forced, due to limited availability, to use wood that would not have been used 50 years ago.
the POC shafts of yesteryear were quite amazing!!

[loon]

Here's a conversion chart from aluminum to what i think may be ASTM spine "size" (deflection)

Code: [Select]

http://www.shootingthestickbow.com/ArrowGuide.html