Wood arrow guys/ Question

[PastorSteveHill]

If I have an uncut shaft spined at 80-84  / 32 shaft/  If I cut one inch off it, what spine would that make it???

[Pat B]

If it was spined like most at 28" then you can subtract 5# per inch over that(20#). Pat

[madness522]

A spine tester measures on 26" so it will still read 80-84 but the shorter it is cut the stiffer it actually is when shot from a bow.  This might be called dynamic spine not sure on the right verbage.

[George D. Stout]

One way to think about it is at 32" that shaft is not 84#....it's more like 64#.  Once you cut it to 28" it will be 84#.  Cedar arrows are spined at 26" for a 28" overall arrow shaft length.  Longer arrows decrease spine, shorter arrows increase spine.  Pretty simple when you think about it.

You must also consider that fastflight strings require stiffer spines as well...usually another five to ten pounds of stiffness.  And....adding weight to the end is like making them longer...they will bend easier.

[Whip]

Just like George says.

[PastorSteveHill]

Ok, so what spine arrow at 31' will I need for an ACS CX longbow pulling 56 lbs. @ my 29.5' draw? Thanks

[George D. Stout]

I sent you a PM Steve.

[Bjorn]

I shoot an ACS CX drawing 48# with arrows cut to 29 BOP. I need 70-75 spine with a 125 point. My guess is you will need 85-90; or build out the side plate a little to stay with what's available.
It does not take much to build out the side plate BTW. I did that to my 53# ACS so I could shoot the same arrows-1/16" was all it took.

[BobW]

Yep.  Another thread stated it as:

add or subtract approximately 4#/inch from the listed arrow spine starting at 26"...

FF string adds 10#, and point weight above 125 requires more spine too

hence the results Bjorn stated:  

3" x 4#/in = 12#
add 10# more for FF (and a smoking high performance bow might need more as it transfers more to the arrow)

48 + 12 + 10 = 70

Keep in mind this is all a starting point.....