Dynamic Spine calculator. .NEW DOWNLOAD AVAILABLE

[metsastaja]

WT don't feel bad I did the same thing before I found Snags post. I was clueless.

[pointystick]

Make sure to use the exact shelf strike plate location of your bow when using this formula. It makes a big difference. I say this because I initially just plugged in +1/8", but when I actually measured my HH Wesley, it measured +1/4" from string centerline to strike plate. Going up to +1/4" gave me 8# less spine than when I used the +1/8" figure.   :eek:  

On the arrow end of things, I like the outcome and plan to test it out and see if it's accurate. The best match I got for my 48#@26" HH is a GT 3555, 29" with 325 up front (100gr. brass insert, 100gr. broadhead adaptor, and 125 gr. glue-on broadhead).  This would give me 580gr. total weight, 12 gpp, and a 27%(  :eek:  ) foc.   :cool:

[Douglas DuRant]

I think if you have a well tuned arrow to your bow already that is different from the bow side this calculator is still of value, because you can plug in a different arrow setup and match the dynamic spine of your good arrow on the arrow side of the chart, and ignore the bow side.

You can also run the test for your other bow setups, and if the error of bow and arrow side calculations are about the same for each of your bows as say 10.5# difference for you then just use that as a correction factor when trying to match a new arrow to a new bow to give you a starting point. Remember to start with the arrow longer than needed when you start tuning it anyway.

[wingnut]

Does anyone have the formula to convert deflection measurements to Spine #s?

It sure would be handy since all the companys are giving deflection now.

Mike

[Douglas DuRant]

It was posted earlier in this thread as 31.5 divided by the deflection as .xxx" or

31.5/.xxx" = # static spine

But when i checked it against my wood arrows the formula seems to come out as 27.5/.xxx" so I don't know if it is right.

I took store bought shafts marked 55-60# and used 57.5# as the spine, and 60-65# as 62.5# and multipled by the deflection as measured on my homemade spine tester to get this formula.

The 31.5 may work for carbon arrows I just don't know for sure. I'll test some GT's and see.

[snag]

What I still don't understand, and maybe never will, is how can an arrow that with a 65# spine NOT fly weak with 350gr tips. I have tried to go up in spine weight with CE Heritage shafts that have 84# spine and if I go above 225gr. they bareshaft weak. At 225gr they fly perfect. So you are taking less spine and adding 125grs more and they fly like darts...?

[Rob DiStefano]

Originally posted by snag:
What I still don't understand, and maybe never will, is how can an arrow that with a 65# spine NOT fly weak with 350gr tips. I have tried to go up in spine weight with CE Heritage shafts that have 84# spine and if I go above 225gr. they bareshaft weak. At 225gr they fly perfect. So you are taking less spine and adding 125grs more and they fly like darts...?

ya think it might have something to do with the archer?    

[joebuck]

Heres a little trick I do to tell if arrow is too weak or stiff.. Get out in a field ( i prefer hilly)on a calm day. pick a spot on opposite hill at least 150yards away. Place your point of aim on the spot. Shoot 3 arrows...If arrows hit to the right of spot.aroows too stiff........hit to left....too weak.........start shooting different arrows of different spines.....till your arrow shoots straight.....this is not rocket science guys. If your arrow can't reach the opposite hill because your bow is too light....drop your bow and do 30 pushups

[DeathBringer]

I've been piddling with this calculator to check my current arrows...have been teaching myself with my old compound arrows, 31.75" 2514's with 125 grain tips.  I knew they were overspined, but until I knew the trad thing was going to stick, didn't want to order new.  

With that setup, the arrows are 82.4 and the bow is 53.3, which makes me feel better about my group size.  

A few days ago I ordered some CX Heritage 250's, planning on using 125 tip with 100 insert at 31.25" and crest wraps.  That should give me 53.5 to 53.3.  Can't wait to see how a more forgiving arrow that's pretty closely tuned to my bow will affect my shooting.

I believe this is the purpose of the calculator...to get a good starting point for us less experienced guys.

[Douglas DuRant]

Ok I checked my Gold tip 5575 and using 75# got 28.5 the deflection measured .340” for me.

Gold tip 7595 using 95# I got 26.6 as the number to divide by the .xxx" of deflection which measured .280” for me.

The Gold tip numbers bracket my wood arrow numbers of 27.5 if I use the high end of the Gold tip spine range as the pounds of static spine. I only used one arrow each for the carbon test.

My spine tester is homemade and may have a degree of error associated with reading it.

[Rob DiStefano]

imo, all shaft spine testing should be in deflection inches, as in days of yore - shaft on 26" centers, 2# hanging weight midway (13"), deflection measured in decimal inches.  this makes for a very common playing field in shaft comparison, no matter what material is used.  

years ago i built a dial caliper spine meter that just measures deflection - i realized early on that converting dial deflection into actual poundage was a wasted effort, and all that mattered were that the arrows (woodies, at the time) each were close in stiffness. a spine meter is good for woodies, for sure.

in any event, there will always be an interpretation as to what shaft "spine" (stiffness) will work best for an arrow that's built a certain way, with a particularly foc and type of steerage, out of a particular bow that's set up a particular way with regards to centershot and what type of string material and nock point heigth, and yadda yadda yadda.  what a pain.  and as stated much in this thread, stu's interactive chart can help those that do need help.

[Douglas DuRant]

Rob, I also feel the deflection is a more useful measure than the poundage range so often used. I have long been frustrated by poundage charts for arrow spine.

I see Stu's Calculator as an improvement over the charts, but would like it in decimal inches of deflection much better, but then most archers don't have spine metters in my experience.

Oh and sorry about the link to Stu's diagram for center shot measurement on the other site. I didn't know.

[Rob DiStefano]

Originally posted by Douglas DuRant:
Rob, I also feel the deflection is a more useful measure than the poundage range so often used. I have long been frustrated by poundage charts for arrow spine.

it's the only measurement that's fact over interpretation.

I see Stu's Calculator as an improvement over the charts, but would like it in decimal inches of deflection much better, but then most archers don't have spine metters in my experience.

i agree about using decimal deflection.  ain't that difficult to build a device to measure shaft deflection - a board, coupla dowels, a ruler, 2# fishing sinker lead, stiff wire, etc.

....

[leatherneck]

OK, I'm a dummy here. How do I figure the static spine for my arrows. I shoot 29"(bop)AD's Trad Lites.  They are total 680grains, with 350 of that up front. I shoot approximately 11.1 gpi. Whats my static spine?

Mike

[snag]

Rob, I agree about checking spine on a spine testor whether it be wood or carbon or whatever.

I don't think it "might be the archer" when referring to the bareshafting of 300+ tip weight on carbons 65# spine weight if cut at or over 29" long.  I shoot a lot. If I am shooting well I will bareshaft so that I am sure my results are good. With 225gr tips the 84# shafts tuned perfect. When I go up above that they consistantly show weak. This is after many arrows.

[kojac]

Call me what ever you want but I think I will just come on here and ask you all, what will fly great out of my new bow   :D

[Rob DiStefano]

Originally posted by kojac:
Call me what ever you want but I think I will just come on here and ask you all, what will fly great out of my new bow    :D  

ummm. a good arra?  :D

[Rob DiStefano]

Originally posted by snag:
Rob, I agree about checking spine on a spine testor whether it be wood or carbon or whatever.

I don't think it "might be the archer" when referring to the bareshafting of 300+ tip weight on carbons 65# spine weight if cut at or over 29" long.  I shoot a lot. If I am shooting well I will bareshaft so that I am sure my results are good. With 225gr tips the 84# shafts tuned perfect. When I go up above that they consistantly show weak. This is after many arrows.

i hear ya, david - if i was you i'd wonder how can that be, too ... but it is.  guess i need to make up vid for you skeptics  :D

[Asafan]

This theme will be terminated then when will not be archers... Except for depth cut (on which paste all in succession) release is very important. The thick and rigid glove (and curve hands) at once will demand a rigid shaft. But a starting point - magnificent. Thank the author     .

[snag]

I hope I don't sound like I don't believe your results Rob. I am just confused as to how this can be when I get such different results. Yep, I'm confused...not the first time!  :confused:  But as long as you are getting good arra flight and I am happy with mine that's all that counts.