spine measurment

[jeffg]

I have a Ace Archery spine tester. It checks spine @26". Most arrows today are spine @28". Is there a rule of thumb or a calculation that will give me the difference if there is any.

[Orion]

Your spine tester is still good.  Wood arrows have always been tested at 26 inches with a 2# weight.  Even though the spine is measured at 26 inches, it's usually expressed as pounds at 28 inches.  

Easton has more recently come up with it's own spine testing formula that uses a 1.94# weight with the arrow suspended between posts 28 inches apart.  It's usually expressed as amount of deflection, i.e., .340, .400, .500, etc.  The results are somewhat different.

I have seen conversion tables published on the internet, but can't put my finger on them right now.

Most suppliers of wood arrows use the 2#@26 inches measurement.  Most carbon arrows are spined using the Easton procedure.  As long as you know which is beingused, you should be able to select arrows right for you, including matching those you already have.

[macbow]

When shooting wood arrows the best use of a spine tester is when you find a arrow shaft that shoots well you can use the reading from this shaft to match others.

When you buy shafts that the supplier marked read them and compare. You'll end up with your own numbers.

[snag]

Shaft size--------deflection---------spine weight
1916================.514===============50.6
2016================.438===============59.3
2018================.383===============67.9
2020================.352===============73.9
2117================.336===============77.4

If you want to find the deflection of say a 50# shaft you can convert the 50# by dividing 26 by 50 = .520  And if you know the deflection of a shaft and wonder what the equivalent spine weight would be just divide 26 by the deflection. 26/.514 = 50.58

[Surewood Steve]

We use all Ace spine testers at Surewood set at 26" centers and use the 2# weight, this was developed 70-80 years age or more and it worked then and it is still working now. Why would Easton try to fix something that wasn't broken is beyond me.  The scale measures deflection and when the weight pull the shaft down say 1/2" or .500 deflection.  Take .26 (or 26") and divide by .500 (or 1/2") and you will get 52, that's 52# of spine.  Divide the length(26")by any deflection and you will get the pounds of spine.  .250 = 1/4", .750 = 3/4" and so on. So the less deflection the stiffer the spine.  Fred Asbell is the only person that has ordered from me and requested deflection.  I had to do the math to get him his 80-85# spine.

[moebow]

Snag, jeffg,  This is interesting.  On my older Adams tester, I get exactly the numbers and arithmetic that Snag posted.  

On my ACE tester, I get:

1916   .415   63#
2016   .355   73#
2018   .375   69#
2117   .325   82#

The ACE is set up on 26" centers and the 2# weight.  The deflection values are pretty different but the arithmetic works for both.  Now I'm wondering what the difference is and which deflection value is right.

Guess I'll have to call ACE and ask in the near future.  Any ideas??

Arne

Don't know how accurate this is, but I got it off of here some time back.

 

Bisch

[Stumpkiller]

That's the one I use.  Two pound weight between 26" centers.

[guspup]

Same here 26" 2 # weight

[moebow]

YES!!!! 2# on 26" centers!! I don't think anyone is questioning that.  I am asking about the apparent difference in deflection measurements between the Adams AND the ACE.  BOTH set at 2# and 26" centers.

Bisch's AMO chart is historically correct, I'm just getting different deflection readings between the two testers.

Arne

[Uncle Buck]

I think whats bothering a lot of folks is that the arrows are measured at 26" but most bows are measured at 28". Don't over-think this, just use what works for your bow

[Bladepeek]

I think Arne has raised an interesting issue. Seems there could be an accuracy standard that all spine testers, draw weight scales, etc should be required to to meet if they want a certification by AMO, or some other recognized standard.

I don't own a spine tester, but it would be nice (if I did) if I could adjust it to match a calibratiion at the mid-range of the spines I'm interested in. Testing a dozen shafts of the same rated spine by several different makers should put the value close I would think.

Of course, unless you are manufacturing arrows, the readings can be used for their relative value if the tester is consistent. If I have an arrow that is supposed to be .500 spine, but reads .520 and it shoots perfectly as set up for my bow, then I will know I want arrows that spine .520 on my tester. Still, if you pay your money for what is supposed to be an accurate device, then you want your money's worth.

I only shoot carbons, and I spine test every arrow I get. There is a wide margin and the shafts (at least Gold Tip because that is all I shoot) are nowhere near what they are marked.

I shoot the XT Hunter shafts, which are the mid-level shaft with an .003 straightness tolerance. The .400 shafts spine out anywhere between 340ish and 380ish. I have put probably 20 dozen thru the tester and NEVER came up with a .400 spine! The .500's spine out anywhere from .420ish to .460ish. I have only done a few dozen of those, but again, have NEVER had a single one come in at .500!

I can only speak for the Gold Tips because that is the only shafts I have tested. I truly think that when they test them at the factory that there are certain benchmark numbers. If the shaft falls between two of the benchmarks, they get thrown in that pile and marked accordingly.

It really does not matter what the shaft actually spines at, as I have the tune figured out for it. What the spine tester does for me is to let me group the shafts in tighter spine groups so I do not have "flyers" as much. If most of the shafts in my quiver are .370ish and I throw one 340ish in with it, there is a drastic difference.

Bisch

[Orion]

OK.  I found the chart I alluded to earlier.  It came from this website (www.RangersArchery.com)  It compares the deflections using both measuring systems.  For example,  a deflection of .52 is obtained for 50# using a 2# weight and 26-inch centers.  For the same 50#, the deflection is .63 using a 1.94# weight on 28-inch centers.  Quite a difference.

Thus, it is important to know which system the supplier is using when you buy your shafts if you order them by deflection wanted.  Or, if you order them in specific spine range, know that the deflection might vary from your own spine tester if they were initially spined using a different system.

[moebow]

Now I feel like a dumb a$$!!  Re-checked the settings on the ACE 107 and found that my centers had slid in a couple inches ----DUHH!!  It sits on my kitchen counter and incidental activity had moved the centers.  So the list I posted above is TOTALLY WRONG -- DISREGARD it!!

Reset to 26 and it is dead on with the Adams tester.  The ACE 107 can be set to either standard, but I usually leave mine on the AMO (26" and 2#) but the thing can be "reduced" in length so the centers can change.  Moral, check things!!  Note to self,  CHECK SETTINGS!!!

Uncle buck  just to clarify, the AMO uses 26" CENTERS, but the deflection given is for 28"  (twenty eight inch) shafts.  Always has been and that does match with the weight at 28" that is common on bows.  Just FYI.

Arne

[Bladepeek]

Bisch, now you've done it!

Now I am going to have to buy/make a spine tester just so I can do the same thing with my shafts.

I've also read that even carbons can have a stiff/weak direction just like woodies.If that's true, then it would seem I need to mark the stiff side as well as sort them. Of course Arne could, if he wasn't so polite, point out that I will have to become a much better archer before it makes any difference   :(

[Orion]

Depends on the carbons.  I've felt a very little difference in some by rolling them diagonally in my hands while pressing one end against a flat surface.  However, I've found it imperceptible on carbons like Easton Axis.  Regardless, not enough difference to worry about it.

I always measure to the stiffest point and mark it on the nock end of the shaft. I align the indexer on my nock to the mark on my shaft.

Like I said above, the main reason I spine the shafts is to get more consistent groups and to help eliminate oddball shafts.

Bisch