1/2 deflection = what spine weight

[Stone Knife]

If my 5/16 arrows for my HH have 1/2" deflection what does that equal in spine poundage.

[Rod Ham]

That should be between 52# and 53# with the standard 26" between the supports and a 2# weight for deflection.  

I just looked on Rose city archery and dug around a little...

 www.rosecityarchery.com/AMOspine.html

[Falk]

Formula goes like this:
26in. / in. deflection = spine in pounds
=>
26" / 0.500" = 53#

or an other example:
26" / 0.300" = 86.7#

If you can measure deflection then, by all means, stick to it and don't mess around with pounds ...

[aromakr]

Falk:
Why?
Bob

[Kelly]

26 divided by .500 equals 52#

The Industry Standard has been pounds and I see no reason to change. Much easier to figure what size arrow one needs for their setup.

Just use this formula, 26 divided by deflection equals pounds, or 26 divided by pounds equals deflection.

[bgram]

Or if it's based on a 28" (center) then it's 56#.  28/.500 = 56.

[Falk]

Bob, thats a good question  

Well, because it was once defined like so. And AMO standard is still 26 inches - whatever Easton etc. may have invented nowadays (e.g. 28"). It was not only defined so, but working quite well too, as bows were more alike and mostly LB's anyway.

To go FROM deflection to pounds had it obvious reason in providing all archers with almost fitting arrows. Only very few had a spine tester themselfs - hence would have been able to measure deflection for their arrows - but everbody knew what draw weight his/her bow had. So that way around was the easiest. Step in a shop and say you need arrows for a 50# bow - and gone.

But, with more modern materials and advanced designs all ended up in big confusion, because each bow may perform ALOT different from an other - even if maximum weight is the same. Think of RC with sight window vs. ELB etc. What was supposed to make thing easy has evolved in a mess.
Knowing the actual deflection of a given shaft would allow to use it with each bow asking for excactly this amount of deflection.

Deflection and "Spine-Pounds" can be converted by formula - okay - but what is happening is, that spine testers already read in pounds. And there I see one problem, cause each of them (testers) is calibrated different and you can't - most likely - compare one to an other without adding a constant factor X to the readings of one of them. But who knows his "X"?

With all the difference in bow performance nowadays the declaration of "spine-pounds" has boomeranged back on us. With a little testing you soon get an idea of what deflection your arrows should have, but WHERE to get them???

Sorry for the lenghty text guys - I got carried away - I suppose. Falk

[aromakr]

Falk:
I have to disagree with you on this one. Deflection in thousands is just as confusing to the un-informed as is pounds. Example Archers one has a 50#@ 28" he draws 29" and cuts his arrows 30" and uses a deflection of .433. Archer two has a 50#@ 28" he draws 29" and cuts his arrows 30" but he uses a deflection of .309 The two are friends and are comparing notes, will they not be confused? Why the difference, well bow number one is cut 1/8" less than center and the second bow is cut 3/16" past center. Deflection does not take into account these factors any more than pounds does. It is a catch-22. And like you said no one spines in deflection anymore and I'm glad.
Bob

[Falk]

Bob,
you are certainly right in that the two friends might get confused on first sight. But every archer has to know his equipment and what he NEEDS to change, e.g. point weight, how long to cut the shaft, plus string material etc. - and all the things commonly know as "tuning".
All this will effect the DYNAMIC spine of their arrows. And the latter is what makes the arrow fly like a laser beam or crocked fencepost.
You'll always start with static spine, measured in deflection, read in pounds, if you prefer.

What I mean is just this: By adding an unnescessary conversion to your measurement, your are adding one MORE source of errors into the equation.

Gute Nacht,
Falk

[aromakr]

Gute:
But in reality you are not adding another measurement, your just reading in pounds instead of deflection. Unless your using a dial indicator then yes you are correct! My spine tester which is an old "Teaser" reads in both deflection and pounds.
And I agree that each archer should know what he needs, however there is so much erroneous information out there that most beginners don't have a clue what to do to correct a problem. Then that bad information gets repeated several times and becomes fact.
Bob

[poekoelan]

If we are talking about wood arrows ( which I think we are ) then I think going by actual deflection instead of spine pounds will cause more confusion than needed IMO. I won't get too far into aluminum or carbon since they are measured differently. The reason they are measured differently is because each one of them deflects the same. Not so with wood. The reason that wood arrows are measured in five ( actually six ) pound groups is because that is the industry standard for obtaining well match arrows. Now if you wanted a dozen arrows all spined at 50lbs or .520, good luck to you.

With that out of the way....
Let's say you have two dozen wood arrows. One dozen is spined 35/40, their deflection reading would be .743/.650. The other dozen is spined 80/85, deflection reading .325/.306.

Notice that as you go up in spine ( stiffer ), the deflection between spine groups becomes less and less EVEN THOUGH there is still only six pounds of variance in a group. Beginners are often confused enough as it is without throwing this into the mix.

Now if wood arrows were like carbon or aluminum and every one of them deflected exactly the same in a dozen, then I would agree that going to actual deflection would be easier.

[Fletcher]

I guess I'm gonna side up with Falk on this one.  I like my arrow's spine to be precise and deflection in thousandths is much more precise for me.  

In the grand scheme of things, it probably doesn't really matter much.  Pounds or deflection, it is just a number that describes a shaft's stiffness.  I commonly use pounds in ordering and conversation as that is the standard that everyone uses.  Very few 50 lb bows however, actually use a "50" pound spine shaft.  We add and subtract "spine" in 5 lb increments for bow type, centershot or lack of it, string type, point weight, arrow length, etc., trying to come up with the right spine.  I know that my hunting setup works best with shafts that deflect .450 inch using the 26"/2lb standard.  Or about 58 lb.    

[aromakr]

Fletcher:
I would be willing to bet, and I don't care who you get your shafts from, that buying a few dozen its next to impossible to match a dozen shafts at .450 and weight match them also.
Bob

[poekoelan]

I'm with Bob on this one. And this is why wood arrows are sold and sorted into six pound groups, which was the orginal premise of this thread. That's one of the reasons why we use pounds of spine to designate them instead of linear deflection. You can match them closer than the standard groups if you want to, but then you have to weight match them too.

A dozen aluminum or carbon arrows can be carbon copies of one another. They can be the exact same spine, exact same weight, exact same diameter. That's just not going to happen with wood.

But back to the orginal premise...Let's say you shoot a 50lb recurve. You draw 29" and use a fast flight string. Well, add 5lbs for the 29" draw, 5lbs for recurved limbs, and 5lbs for the fast flight and you are in the ball park. How would you express this in linear deflection keeping in mind that as spine groups go up, there is less deflection among the six pound groups?

[Stone Knife]

There sure has been a lot of info shared here, i would like to thank everyone who has replied. My original intent of this post was to try to find out what the spine weight is on wood arrows for my Howard hill Bigfive. The bow is 66" 48# @28" i draw 27". I have ordered arrows from HH and they fly well out of the bow, recently i have been dabbling in arrow building and wanted to make up a dozen for my Hill. My tooling at this point in time is very limited, i have no spine tester. All i know is that the arrows i have now are .500 deflection, this is what Craig told me. The shafts are 5/16 dia. With the info i have received here i was going to order some shafts 5/16 dia. spined at 50-55 Would this be the proper shafting for my bow?

[Falk]

by Stone Knife: "With the info i have received here i was going to order some shafts 5/16 dia. spined at 50-55 Would this be the proper shafting for my bow?
"

... depends on whom spined them out - might be yes - can be no   :p   :D    :cool:  
Ah and don't worry Stone Knife, we wont start a fight about that subject here, wont we?!
-----

Austin, yes, I meant woodies, but it doesn't matter or affect the principle which material. Short while ago Littlefeather or JC or Ray Hammond or ??? told me that he found HUGE spine differences within his carbons! I thought they were all alike but NO. You may not notice it though. Obviously due to the other qualities of carbon - recilence (?word) etc.

Bob, I think you will win your bet with Fletcher. But searching for shafts which have the exact same deflection in .001" is nonsense for all except FITA archers maybe. But why not try to get as close as possible to it? At least you are able to get finer increments then 5#
Problem No.1 with spine testers is their calibration IMO. A micrometer tester has no probs here and is certainly better then others. But I dont have one either.

You are right with what you sayed about beginners might get confused etc. but why not start telling them the principle behind it and make them understand?
I know of pro shop owners who DONT understand "spine" - but are teaching beginners  

[aromakr]

Stone Knife:
If you are going to cut the arrows to 28" BOP, I believe you will be where it should be. I shoot hill bows also and usually spine them to bow weight cut to 28"

[aromakr]

Gute:
I agree with you however, No one here in the states spines too deflection anymore, everything is in pounds, so its not good to teach someone deflection when pounds is what they will be exposed to. And I do agree about proshop people, the blind teaching the uninformed. To make matters worse is Easton spines are 28" centers with a 1.94# weight.
This has been fun!
Bob

[Van/TX]

Agree with Bob as usual. The 100 year old system that we now use ain't broke  :D ...Van

[Falk]

Hi Van   :cool:   see below    

I think the leading question is solved and for the fun of it, we can "went academic" without doing harm to the thread ...
To further confuse the subject AND to show HOW things DO change even if they were used for ages in a particular manner - please allow me to quote James DUFF (1931: 12) himself:

"Prior to 1912, the expression "Spine of the Arrow" was to the best of my knowledge never seen in print, and seldom used outside of the archery tackle making shops in Britain, but there it was an everday expression by makers.
About the above mentioned year I used the expression in my reply to Professor Rendtorff, and since then pages if not volumes on the subject have been written until we don't know where we are today.
Whatever the latter day meaning may be taken to be, the original term was a simple reference to the actual return or as to how resile the shaft may be. Rigidity had not place in the thought of those speaking on the subject." (highlights in text above by myself)

I think we all agree about the convenient and the "exact" way - and what it's all about?! And I hope the above quoting may be of special interest for you on how it had once all developed. Therefor I shall also give you some refrerence below - which is interesting reading on the subject - and how it all started with spine testers ...

Cheers, Falk    

Literature [in chronological order]:
RAWLINGS, B.L. (1930): A Plea for a Standard Method of Guaging the Spine of an Arrow. - Ye Sylvan Archer, May-June 1930: 3-5, 1 fig.
MORRISSEY, F.R. (1931): Gauging the Spine of an Arrow. - Ye Sylvan Archer, Jan. 1931: 5-8, 1 fig.
YATES, J. (1931): Spine Controversy Reaches England. - Ye Sylvan Archer, May 1931: 11-12.
DUFF, J. (1931): The Spine of an Arrow. - Ye Sylvan Archer, May 1931: 12-13.