Spine tester question.

[Buemaker]

I have a Flight Rite spinetester that I bought from Alan Rothar years ago. English not being my native language I hope you understand what I mean. Up to about 60 pounds it seem to be accurate, that is when I divide the deflection in inches with 26 it corresponds well with the stated pounds on the scale. When the shafts get stiffer this is not the case.
Are the newer spinetesters more accurate and is there any accurate spine charts available? Thanks Bue--.

[LittleBen]

The problem is inherent to spine testing. Since shaft length does not increase as spine increases, deflection decreases. Therefore resolution decreases. It is a poorly designed testing environment because as spine increases the differences in deflection become nearly impossible to measure.

You might make your life easier if you can figure out how to spine test the full length shafts, in other words increase your centers from 26" to 30 or 32"

[Buemaker]

Thanks. I have another question. According to wood arrow spine charts a spine deflection of .520" with 26" centers and a two pound weight shows that the spined shaft fits a 50 pound bow, 28" arrow lenght. That corresponds well with my spinetester. But what arrowpoint weight is considered here, is it 125 grains or-- ? Thanks. Bue--.

[Roy from Pa]

I don't believe any point weight is considered there, Bue. The spine checkers just tell you what spine the arrow is. It's a starting point.

[Brock]

no arrow weight is considered in the mix.  First, make sure you are testing the spine of the wood shafts with the grain going perpendicular to the bar that presses the shaft.  This is its strongest side as having the grain parallel to floor will be weaker.

Do this every time...  I will measure....rotate shaft 180* to the opposite side but still with grain vertical and do again for consistency.  If I am looking for a range I will then measure the flat grain sides as well.  Not perfect but works for me.

I dont worry about how arrow length and points affect them...that is not the point.

The device ONLY measures STATIC SPINE...deflection of wood shaft itself with no other inputs.  The 26" spread makes no difference as most important that they are all measured with same distance and process.

Before you buy your shafts or start weighing and sorting you should have identified your point weight, draw length and therefore arrow length.  Most add 5# for every weight increase over 125gr for points...and 5# for every inch over 28".  Some other considerations like how clean your release is....if shooting no stretch string...design of bow (center shot vs non-center shot) like recurve vs selfbow.


taking the static spine you measured on your spine tester and then doing the calculations for your point weight, draw length, FastFlight String, Center Shot or Not, etc....and it gets you in the ball park for your arrows.

You can further fine tune by changing point weights...or brace height.  I prefer brace height.

Good luck.  I am sure I confused you more.  

[mikkekeswick]

I made my own spine tester and it is easy enough to get accurate readings on shafts upto 100# spine by using a good design on your testers arm eg. fulcrum point and length of arm past it.
I agree with Brock on all his points.  
The fun comes when you order wood shafts and see for yourself the huge discrepancies in spine,weight,straightness,grain straightness etc etc!!! Buying wood shafts is what I think is described in the USA as a crap shoot!
I have been making my own shafts from boards for a good few years now and after making a quite a few thousand I have learnt that arrow making is a very good way to learn about woods properties and just how much variance there is in even the same board let alone the same species of wood. Purpleheart makes awesome shafts by the way.

[LittleBen]

As th others have said, the spine rating (I.e. 50#) does not consider point weight. It's just to give some more meaninful value than .520" so that it's easier for us all to talk about.

It might give some general idea of what stiffness shaft you need, but it's rarely 50# spine for.  50# bow as I'm sure you know already.

[LittleBen]

I built my spine tester like this, except that it's made for tabletop use instead of on a wall.
 http://poorfolkbows.com/spine1.htm

Those calipers are very accurate, make it allot easier.

[Buemaker]

Okay thanks, then I have one more question.
If I moved the centers from 26" to say 22" would the same math apply: 22 devided by inches deflection = pound weight for a 24" arrow.
Bue--. (square head)

[fujimo]

a side note, most commercial manufacturers use automatic spine testers- which measure the shaft in a random configuration( not parallel to grain etc) this enables them to be productive, and competitive in their pricing.

i have found many shafts that actually test stronger/stiffer on the flat side, as apposed to parallel to the grain- not many- but more common than one might think.
i have also found that the difference between the flat and grain sides dont vary more than a few pounds ( on good, tight grained, old growth shafting)

when i spine my shafts, i check all 4 quadrants- then  choose and mark the sides i want to use, if i want to keep the spine exactly the same- i dont consider grain orientation at all.

measure some carbon shafts- you will see variances in spine too, depending on orientation

[fujimo]

i love sam harpers site- its always a good read, and he really make an effort to keep costs down.
only one question though, with all those spine testers , the arrow is sitting on raw material, wood or steel, does that not induce friction, should they not be on a "bearinged" surface, so that the supports will roll as the arrow shaft flexes- would this not be more accurate??
or am i really splitting hairs here-
would be good to have  a "spine off"- with a gaggle of testers in one place, and all to test the same arrow, test some carbons- test flats vs parallel etc etc

[Brock]

I think you are making it way more complicated than it is Buemaker.

This will get you started in general area..
 http://www.finefletchings.com/arrow-guide/#WhatSpine


Then use your spine tester to find shafts that are within 5# of your desired spine based on the earlier calculations.

If the arrow shoots well...leave it alone.  

[LittleBen]

Originally posted by Buemaker:
Okay thanks, then I have one more question.
If I moved the centers from 26" to say 22" would the same math apply: 22 devided by inches deflection = pound weight for a 24" arrow.
Bue--. (square head)

No. Well maybe, maybe not.  There wouldn't be any advantage to knowing the answer anyway.

All that matters is that your shafts are grouped together by spine and labeled. Unless your selling the, to others, all that matters is that your system is consistent.
Then just tune as normal by shortening the shafts or adding point weight.

[Wolftrail]

I built a spine checker as opposed to a tester. I buy professional wood shafts that are all within a couple pounds of each other.  I made a mark on the wall for those given shafts and compare. Basically stay within a 3/16" above or below. Preferably above.

[LittleBen]

Originally posted by Wolftrail:
I built a spine checker as opposed to a tester. I buy professional wood shafts that are all within a couple pounds of each other.  I made a mark on the wall for those given shafts and compare. Basically stay within a 3/16" above or below. Preferably above.

If you used 26" centers to do this your spines could be off by as much as +-20#.

Let's say your professional shafts are 50# spine exactly. They deflect .520" under a 2 pound weight. 3/16" more deflection is ~.700" and would spine at 26/.700=37#. 3/16" less deflection would be .340" which is 26/.340=76#.

IMO there is no way to accurately spine without measurement of deflection with accuracy of .005" and the higher the spine is the more accuracy you need.

From 51# to 50# there is a deflection difference of ~.010". From 71# to 70# there is only a deflection difference of ~.005".

[LittleBen]

Double post

[Wolftrail]

Originally posted by LittleBen:
 

Originally posted by Wolftrail:
I built a spine checker as opposed to a tester. I buy professional wood shafts that are all within a couple pounds of each other.  I made a mark on the wall for those given shafts and compare. Basically stay within a 3/16" above or below. Preferably above.

If you used 26" centers to do this your spines could be off by as much as +-20#.

Let's say your professional shafts are 50# spine exactly. They deflect .520" under a 2 pound weight. 3/16" more deflection is ~.700" and would spine at 26/.700=37#. 3/16" less deflection would be .340" which is 26/.340=76#.

IMO there is no way to accurately spine without measurement of deflection with accuracy of .005" and the higher the spine is the more accuracy you need.

From 51# to 50# there is a deflection difference of ~.010". From 71# to 70# there is only a deflection difference of ~.005". [/b]

So I exaggerated how about 1/16"      :eek:

[Buemaker]

I hope it is OK to post this link.
 http://www.arrowskp.com/Spine_Charts.html

[Buemaker]

And this.
 http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=075678;p=2