Spine testing question...

[toomanyknots]

I recently made a spine tester based on this build along here:

http://www.primitivearcher.com/smf/index.php?topic=4589.0

What I am wondering, is where he says to make the pegs "13" from center if your shortest arrow is going to be 26". I was wondering, wouldn't you measure 13" if your shortest arrow was gonna be 28"? And this is measured from the bare shaft? Not the shaft to the point, right? I made mine with 26" static pegs, and measure 28" arrows on it. (28 1/2" or so if measuring from the point of the head to the end of the nock). Is this wrong? 

[sharpend60]

Nope. Not wrong.

I believe it is AMO standards or some such 'offical' archery BS.
Regardless of who endorses it, all major manufactures use it... And if you are selling arrows you should also. Because thats what folks expect.

2 lbs wieght and 26" posts.

If you buy .500 (2018?) aluminiums thats what they are measured at.

You're in the clear.

I'm glad ya got your own built instead if paying through the nose for one.
That drives me nuts...

[toomanyknots]

And if you are selling arrows you should also. Because thats what folks expect.

I just made my first (hopefully) correctly spined arrows a couple days ago. I am definitely not selling any, haha.

I'm glad ya got your own built instead if paying through the nose for one.
That drives me nuts...

Ya, you convinced me, . I was just confused about this build along in particular, as I don't understand why it would say to make your posts 26" apart to measure a 26" arrow?

[sharpend60]

26" apart for any arrows. Even 46" arras.

Its just an industry standard, blame Bob Lee.

[John D]

The spine tester magnifies the deflection caused by the 2 lb weight.  The magnification ratio (length of the indicator needle is one factor)  was worked out using posts 26" apart.  Doesn't matter if the arrow is longer, because its testing the stiffness, which is theoretically independent of length (wood has character, and that kinda messes with theory).  I'm guessing here, but it would seem that we're interested in stiffness where the arrow paradoxes: the middle. 

[osage outlaw]

I believe you add 5lbs for every inch under 28".  Spine your arrows full length and then do the math when you cut them down.  I'm not sure how exact it is.

40 lb arrow @28" = 50 lb arrow @ 26". 

I don't have anywhere near a 28" draw but I leave my arrows full length.  I like the extra weight.

[Pat B]

Like said above arrow spine is measured on a 28" arrow(from behind the point to the throat of the nock) by suspending the arrow between 2 uprights 26" apart, with a 2# weight hanging from the center. For arrows longer than 28" you can subtract 5# per inch from the indicated spine weight and add 5# per inch for each inch under 28". This spine is figured with a 125gr point on the arrow. Heavier points reduce the effective spine weight and lighter heads add to the effective spine weight.
 So, a 30" arrow with a 125gr point spined at 50# will shoot like a 45# spined arrow and the same arrow cut to 26" will shoot like a 65# arrow.

[toomanyknots]

Like said above arrow spine is measured on a 28" arrow(from behind the point to the throat of the nock) by suspending the arrow between 2 uprights 26" apart, with a 2# weight hanging from the center. For arrows longer than 28" you can subtract 5# per inch from the indicated spine weight and add 5# per inch for each inch under 28". This spine is figured with a 125gr point on the arrow. Heavier points reduce the effective spine weight and lighter heads add to the effective spine weight.
 So, a 30" arrow with a 125gr point spined at 50# will shoot like a 45# spined arrow and the same arrow cut to 26" will shoot like a 65# arrow.

Thanks for the move, sorry about that, bows was obviously the wrong place to post an arrow question. Sorry about that. Anyway, to make a 28" arrow, if there is about 1/2" of shaft that the nock will sit on, than should I cut the shaft 28 1/2" long, so when the nock is glued on the shaft will measure 28"? Also, these arrows are self nocked, so do I not have to measure from the throat of the nock if it is self nocked?

[Pat B]

The throat of the nock to the back of the point is the measurement whether it be self nocks or plastic add ons. Probably cutting your shaft to 29" will give you 28" from the throat of the nock to behind the point.
 I prefer longer arrows. I cut my shafts to 29" to 30" for my 26" draw. I think a longer arrow gets better clearance around the bow plus I like the extra weight I get with a longer arrow.