How specifically is spine measured?

[Krokett]

I've been trying to get cedar arrow shaft/arrows, but I still haven't found the answer to the following question;
Is the given arrow spine for a shaft/arrow always measured at full length (32" usually) or at the length it is cut at?
The static spine values for full shafts is always given, but it doesn't tell me what it'll be at my desired arrow length. I am aware that spine increases as the shaft gets shorter, so what spine do I need to get for a 55#@28" if I want to get my arrow to have a 60-65# spine at 29 length(according to charts)?

[Bjorn]

You don't say if your bow is a LB, RC, or R/D LB; and whether or not you are using a 'modern' string. In any event there are two pretty good calculators that I have used. One at the Morrison site and the other at ACS bows. That should give you a pretty good idea of what you need.

[Krokett]

It's a 62" recurve with a FF string.
I tried those sites but couldn't find the calculators. Thanks, though.

Is there any rule-of-thumb or any way to check a chart and figure out which arrow spine at full length are right for me?
I.e. I see charts and given spine values for cedar shafts - in my case a spine of 60# appears to be appropriate for my bow - but if I order the shafts at full length and with a spine of 60# by the time I cut them to 29" the spine would have changed quite a bit.

Maybe, I didn't phrase it correctly the first time around.
Admittedly, I am just testing, trying to find the right arrows for me. I have bought some carbon and cedar for testing purposes, and even though I like the carbon arrows, there's something - how should I put it? - 'organic' about the shooting feel of wood arrows.

[Krokett]

I just came across something...

As found in

 http://www.archers-friend.com/arrow-length.html

"First you need to understand about spine ratings or poundage recommendations. Say a bow or an arrow shaft is rated for 50-60 pounds. It is generally accepted that this means AN ARROW LENGTH OF 28 INCHES WITH A 125 GRAIN POINT."

So, measuring the spine is a standardized procedure where the arrow measured is 28" long and has a 125 gr point?

[wtpops]

Originally posted by Krokett:
Is the given arrow spine for a shaft/arrow always measured at full length (32" usually) or at the length it is cut at?
 

The spine is mesured on a wooden shaft at 26" and on a aluminum or carbon shaft at 28"

So if you buy a set of shafts at 60#, that is 60# at 26" not full lenght

[Bjorn]

Krocket my apologies; I should have checked beforehand. It seems to me they were there at one time-or just old brain cells on my part.............OK. I shoot only wood, and here's what I do.
Bow weight-55@28 (assuming you draw 28)
Center cut RC add 5; FF string add 5; 29" shaft add 5 more (one inch over 28).........this puts you at 70#; and should be pretty close. I would get a couple of different shaft# and bareshaft them. Ted at Raptor archery will help you out.

[gilf]

Krokett - Give this a go. It's great for working out a starting point.

 http://www.heilakka.com/dynamic.htm

[moebow]

Guys,  Here's a "blurb" I did on another forum.  It is a brief discussion on the "5#" rule for wood shafts

For example, if you have an 11/32 shaft that
has a spine rating of 30#.  It will have a effective spine of 35# if cut to
27 inches and a spine of 25# if cut to 29 inches.  Remember that wood shafts
are spined between 26inch centers with a 2# weight.  The inches of
deflection - as measured on a spine meter  divided into 26 will give you the
spine rating for the bow you are shooting.  For example,  If you have a
shaft that has a .500 deflection on the spine meter,  26/.500 = 52#.  So
that shaft cut to 28 inches should work well in a 52# bow.  28 inches is the
base measurement for the 5# rule you all have been talking about.  By the
way,  the use of 26 inch centers and a two pound weight just happens to work
out for 28 inch arrows.  This has been around a long time  and is
information based on the "old timer's" knowledge and experience.  If I
continue with the above example  a traditional 52# Hill style bow with
dacron will probably shoot the .500 spine arrow pretty well drawn to and cut
to 28 inches..  Now  It's +5# for each inch over 28 inches, -5# for each
inch less than 28.  Plus 5# for fast flight strings, Plus 5# if you shoot a
Reflex/deflex bow or a recurve.  Also the traditional target point weight is
125 grains so if you're using a 150 or 175 grain point, you'll probably have
to add 5# for that.  If a lighter point subtract 5#.

 This is a pretty effective way to ESTIMATE
what spine to order for wood shafts and frankly it's not bad for aluminums
too.  As mentioned above, the manufacturers have published Aluminum and carbon spine ratings based on 28 inch centers (I have no idea why) but if you use a standard spine meter with 26 inch centers and a 2# weight with aluminum or carbons you will get similar results.

[Bill Carlsen]

A shaft spined at 70-75 with a 125 grain head will probably work very well for you. Perhaps even a 75-80.

What moebow posted is pretty close to being the rule of thumb although the actual spine is measured in thousands of an inch in deflection....but that is another story. What he said is good to work with.

[George D. Stout]

You guys are reading too much into it.  The span of the spine meter is 26"...where the pegs set.
The arrow is spined there for an arrow that will be around 28" long (not 26"....the spine length).
An arrow that spines 55# on a 26" span with a 2# weight, will work great for a 55# bow and a 28" arrow.  This was figured with standard points of the time which normally were about 125 grains.

For each inch shorter than 28" (not 26") you add 5#, and for each inch longer your subtract 5#.  All this still considering a 125'ish grain point.

The variables will be greater once you start fooling with heavy points, and are not static.  Each persons style, bow, brace, et al, enter into the picture.

Bill Carlsen is right about what will work for what you ask.  This spine thing has been misinterpreted so much lately....just need to look back at how it was set-up.  A 2# weight over a 26" span, for an approximately 28" arrow/draw.  If you follow that simple example, and calculate for tip weights and arrow lengths, you can get in the ball park rather quickly.

[Krokett]

THAT's what I was looking for!

Thanks to you all!  

@ Gilf: Thanks. I will try that!

[moebow]

Bill,  You're right.  I used .500 to indicate that the deflection is measured in thousands.

George,  I believe that is what I said.  26" centers, 2# weight produces a spine starting point for a 28" arrow.

[George D. Stout]

You did indeed moebow, but others are quickly confusing a simple process.  By the way, it has only been a little over fifty years that we have known much at all about spine as it applys to arrows.

[moebow]

Yep, about 50 years.  Been there for all of them and then some.

[wtpops]

Learn something new every day, love this site, you can learn more here in 2 months than a life time of trial and error.

George and moebow thanks for the info and to think I have been think wrong on this for a lot of years.

Man I wish everything was listed as deflection at 26" or 28", 2# or 1.94#, just standardize it so we all talk the same language.

[moebow]

wtpops,  Like I said above, I have NNOOOOO idea why the manufacturers went to 28" and the 1.94 pound standard.  If they had stayed with the OLD standard, I think 100% of the confusion on the three different arrow materials would be gone!!!!!  Spine ranges of 20 pounds or so with the carbons then fuss with length AND point weight is just too much for this old head --And far too much work.  Using the 5# guide above you have solved (within reason) the length and point weight question.  Yes you can still further fine tune them but I respectfully submit that a majority of shooters won't be able to improve arrow flight much.  I know I haven't.

[Gatekeeper]

Thanks George your explanation helped simplify this issue for me but, I have to ask about point weight. Is there a rule of thumb for the point weight that is similar to the +-5# rule that is applied to the shaft length?

Example, add one pound of arrow spine for every 10 gains of added point weight. Something along this line

Thanks again.

[moebow]

Gatekeeper,  I think you're trying to cut it too fine.  Consider a 5# adjustment for a point change of 30 to 40 Grains.  Wood arrows are seldom so homogenious (consistant) that ten grains will be noticeable.  Another way to say it is that wood,especially, is more forgiving than the other materials.  Also I'd point out that shafts are usually sold in plus or minus 20 grain groups and in 5 pound spine ranges.

I personally would not try to deal with shaft spine adjustments of less than 5# increments.

[Gatekeeper]

Okay, moebow thanks.

Using the formula that you and George have provided this is what I come up with. Please look this over and tell me if what I have calculated is correct.

55# bow drawn to 29”

30” arrow with 250 gains up front.

55# arrow spine + 5# +5# (2” over 28”) = 65# spine for a 30”arrow with a 125 grain point.

To compensate for the extra point weight of 125 grains, I need to divide 125 grains by 40 grains.

125 grains / 40 grains = 3.125 * 5# (of arrow spine for every 40 grains) = 15.625# of extra spine need in the arrow shaft.

65# spine + 15.625# (extra spine) = 80.625# spine

So I should use shafts that spine 80# – 85#.

[George D. Stout]

Gatekeeper, that's some fancy cypherin' but I think you would be very close the mark.  Still, with ultra heavy heads on cedar, you would want to experiment in those ranges before dropping the money for a matched dozen.