arrow making spine question

[Dick in Seattle]

I just finished making my first set of wood arrows.  I want to make more, but I'm confused on one point relating to spine.   I bought two sets of shafts... one regular POC set from 3 Rivers and one set that had had hardwood footing installed.   Both sets were purchased as 45-50 spine.   I cut them to 28".  Both sets ended up spining 50 - 55.  I'm assuming that they stiffened up when cut.

 I'm happy, the set I finished, the unfooted ones, shoot really well for me in several bows.   However, before I buy more shafts, I need to know if this is normal... i.e. if you buy shafts rated at 45 - 50 and have them cut, they end up stiffer.   If so, fine, I'll just keep ordering that way, but if not, I got stiffer shafts than I ordered and to duplicate them I should order 50 -55.  

Any advice will be appreciated.

Dick in Seattle... who will start on his second set this week.

[SCATTERSHOT]

Dick, the spine will remain the same on the spine tester, no matter the length. The DYNAMIC spine will get stiffer as you cut the shafts, but the actual spine will remain the same. Imaging a 36" shaft, for example. you can break it pretty easily, without much effort. Now imagine breaking it into shorter and shorter pieces. It gets harder to break, until at 6" or so it's a pretty tough little stick. That's dynamic spine. It's the same piece of wood, but it acts stiffer as it gets shorter.

[dino]

Dick,
Sounds to me that you bought 45-50 shafts from two different source and they spined for you at 50-55.  I would start with checking your spine tester. Cutting them shorter will not change the static spine of the shaft.  Find an aluminum shaft with a know deflection and check your spine tester first.  dino

[Orion]

Yep.  I'd check the spine tester as well.  Looks like you lucked out though.  Most bows actually shoot better when the arrows are overspined a little.

[Dick in Seattle]

dino...  help!  I guess I need to understand this.  I found a deflection chart for eastons, went downstairs and put a 1916 and 2117 in the spine tester, calibrated it, and put the weight on.   Obviously, I'm doing something wrong!   It was wildly off the chart.   I almost panicked and then realized that the deflection chart stated "on 28' span".  Well, my spine tester is a 16" span, if they're referring to the distance between the two pressure points.   Somehow, I though there was a standard distance for this for spine testing.   obviously, there's something I'm missing.

Dick

[Grey Taylor]

Scattershot is spot on.
If you want your spine tester to be in line with the others, 28" centers is the way to go.  What spine to choose depends partly upon the arrow length.  If you're shooting a 31" arrow and you want 50# dynamic spine, you need a much heavier spined shaft.  If you're shooting a 25" arrow and want a 50# dynamic spine, you need a lighter spined shaft.  If you're shooting that magical 28" arrow and want it to spine 50#, then buy shafts spined at 50#.

Guy

[poekoelan]

I always thought that for wooden arrows, spine was measured on 26" centers with a two lb weight and that Easton measures their aluminum on 28" centers with a 1.94 lb weight.

[Chuck Nesset]

I'm with poekoelan on this one, both my spine testers are on 26" centers with two pound weights. Cutting an arrow to 28" won't change the deflection on this type of spine tester.

[Dick in Seattle]

All I can assume is that the Ace spine tester that I have, which has 16" centers, has a readout panel that is adjusted for it's weight.  I guess that makes sense, but it is sure causing me some confusion.   I think what I'll have to do is get a couple of different arrows weighed on some other, more sophisticated tester, and then "adjust" my Ace accordingly.  This would be a very scientific adjustment... you bend the needle...

thanks for all the input, guys.   it helps, even if I am still kind of stuck looking for a "working answer", as opposed to an absolute one.

Dick

[Grey Taylor]

Crap, I just measured my tester: 26" centers.  Sorry for contributing to the confusion.
But I stand by the other stuff    

Guy

[dino]

Dick,
An Easton spine chart will not give you an accurate deflection for your spine tester.  As stated above, Easton's chart is base on deflections of shafts on 28" centers with a 1.94 lb weight.  I have on of the Ace wall mount spine tester.  Nice little testers but they still have to be checked.  It is based on the old AMO standard 26" centers and a 2 lb weight.

I would first of all double check your weight.  On that tester it should be 1 lb.  Make sure it is and exactly 1 lb, that will effect the readings.  Secondly, I would get a variety of aluminums and spot check the readings.

Shaft       Spine    Deflection
1816         42      .628
1916         50      .520
2016         59      .438
2018         67      .382

These are just a few, but they should read EXACTLY or the tester is off.  This is where "close" is not acceptable.  If you don't have these and have some other aluminums just pm me and I can get you the spine and deflection on what you have.

[aromakr]

As you can all see from the above posts there is quite a bit of confusion on spine. Keep in mind there are TWO standards. The real one 26" centers with a two pound weight. and the Easton Standard, 28" centers with a 1/94# weight. Spine for traditional bows should be measured on the first standard (real one). Dick you will find variations in spine testers as like may those that created them did not fully understand the concept. I've never found two testers that measured exactly the same, however in there defense, we are getting too techinal with spine, a couple of pounds will not make that much difference. As I've said many times this "Ain't rocket science". Before the spine tester arrowsmiths just flexed the shaft in their hands to measure its stiffness.
Bob

[Van/TX]

Dick, you need to calibrate the tester with a known spine shaft (aluminum) but don't bend the needle. Either move the scale, change the zero point or tweak the weight....Van

[DarkeGreen]

If you think about the "real standard" and the "Easton standard" real hard you see they are both one and the same. By moving the distance between the two supports the arrow flexes more, by using a lighter weight the arrow flexes less. The two offset each other. That's why the weight of the Easton standard is 1.94. Engineering show the more movement the needle makes the more accurate the measurement. Either way the numbers will be the same.

[Dick in Seattle]

you guys are fantastic.  Once I get my morning coffee in me and become human, I now have more things to test.

Dick

[dino]

Darke,
Deflection of an MFX 400 on an Easton tester is .400 on a "real spine tester" the deflection is .310.  The deflection of and MFX 340 on an Easton tester is .340 and the deflection on a "real spine tester" is .268.  The deflection measurements are different between the two testers. dino

[Bob@Ace]

Dick,
I can assure you that your Ace Spine-Master was carefully calibrated before it was shipped to you.
It is calibrated so that the deflection is the same as the AMO standard, which is 26” between supports with a 2 pound weight.  That deflection is divided into 26 to give spine pounds.  It is different than the Easton method that shows about 22% more deflection.  The AMO standard has been used for nearly 100 years.  
Wood shafts, especially unsealed ones, will typically spine stiffer in cold, dry winter weather, and spine weaker in hot, humid summer weather.  The same shaft can show a difference in spine of 3-5 pounds as the weather changes.  After your shafts are sealed, you can expect less variation and it will take longer for it to show.  Usually that small change in spine can be compensated for, by a few twists in the bowstring to change the brace height.  By twisting your bowstring to shorten it, and raising the brace height, you are effectively increasing dynamic spine.  By untwisting the bowstring, and lowering the brace height, you are lowering the dynamic spine.  Some of the large volume shaft suppliers measure the spine on automatic machinery that doesn’t orient the grain consistently the same way.  So if you properly orient the grain on your Spine-Master, you may get a different reading.  

We carefully calibrate each Spine-Master after assembly, and check them with test shafts at high and mid range to assure accuracy.  But to assure yourself, I suggest you test it with an aluminum shaft, if you have some handy.  Easton aluminum shafts are usually very consistent,  + or -  1 pound normally.  Below are some aluminum shaft sizes and their spine by AMO standards.

1916   53-54
2016   60-61
2020   74-75
2213   69-70
2216   84-86

If you prefer, you can talk to me in person, by calling our toll free number that’s on your Spine-Master.


Bob Mayo
Ace Archery Tackle LLC

[Dick in Seattle]

well, blast!   The weight is exactly on at 1#.   However, the readings are off.  

1816 alum should read .628 but reads .530
1916 should read .520 but reads .465
2018 should read .382 but reads .380

tester was carefully zeroed each time.

Bending the bar would accomplish nothing, as it is the range from zero you're looking for.   Adding weight might, but...

I'm calling the Ace company later and see what they have to say.  I'll report back.

Dick

[DarkeGreen]

Thanks for the correction.

[FJTOYMAN]

Dino,
How are you figuring your deflection? I'm in the process of building a spine tester like this one.  www.jamesmhill.com/Spine_Tester.  
Your deflections don't match the ones posted. Which is correct?
Thanks