# Dynamic Spine Calculator and Olympic Recurve Help



## limbwalker (Sep 26, 2003)

don't see the screen shot.

With those specs, you're going to be in the 800-900 spine range, assuming you're using a long stabilizer. If you're shooting barebow, then the 800-700 spine range.


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## Noupoi (Feb 15, 2015)

Whoops, complete forgot to attach it.

http://i.imgur.com/ssMHuXN.png

I am using a long stabiliser. The 800-900 would be group T2 on the Easton chart, correct?


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## limbwalker (Sep 26, 2003)

Too early in the a.m. for me to do math. I'll check in later.


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## leschrader (Jun 26, 2012)

Noupoi,
You didn't include the "footing" value. If your using nibbs, that will be around 1.1 inches......you need to measure the tip. The footing value is any tip length inside the shaft over .9 inches. Down load the latest version of Stu Millers program, it explains the different input values and how to measure them. The program shows a 1616 with a 63 grain tip or a 1716 with 110gr tip for a better front of center (FOC). Generally, you want to keep your FOC between 10 and 15%. For indoor, you can drop down to as low as 6%, but for out door distances, no less than 10%.


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## Noupoi (Feb 15, 2015)

Taking a 1716 shaft as an example, how would I enter the footing value for it?

Easton's website quotes the weight for NIBB point for the 1716 as 60 grains. Would I enter point weight 60, 0 insert weight, yes footing, and footing length 1.1"?

With the version of the calculator, is rev 5-12 2007 newer than 12-25-10? I thought I had the latest one!


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## leschrader (Jun 26, 2012)

The latest version is on this page:
http://www.archerytalk.com/vb/showthread.php?t=2194522&highlight=stu+miller

The footing is the actual length of the nibb that is inside the shaft minus .9"....so if the nibb is 2" long, the footing value would be 1.1". In effect, you are doubling the arrow wall for that length which would be the same as shortening the arrow. There are tabs on the bottom left of the program page that explain all the values and definitions. This program will only give valid arrow specs if valid values are input. Don't guess, measure. Since I have been using this program, I haven't wasted a single dollar for arrows on a guess for myself or any of my students. It's a great learning tool for understanding the interaction of the componets for dynamic spine values. If you don't have a weight scale that measures in grains, you need one......there are some for around $20 to $25, that work great for what we need, through the online gun supply sites that carry reloading equipment.


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## Noupoi (Feb 15, 2015)

Thanks for the detailed reply.

I decided to re-measure my draw length a few times, and it turns out that it's closer to 28.5". I've entered this into the new version of the calculator.

I've also added a +13# value to the draw weight to compensate for having a pressure button as suggested in the thread you linked.

The new values come very close to what Easton's charts suggest, which seems very good.

The two options that work with the calculator are:
27.75" 1716 shaft, no insert, NIBB points, 3x Flex Fletch FFP-225 vanes, Uni bushing, Large G nock
27.75" 1813 shaft, RPS insert, NIBB points, 3x Flex Fletch FFP-225 vanes, Uni bushing, Large G nock

The second option has a better FOC, so that looks like a much better option.

Additionally, I've come to realise that as I can play around with the spring tension and centre shot, I have a lot of room for adjustment.

How do the new values look now?


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## leschrader (Jun 26, 2012)

Noupoi,
I wasn't able to find a reference to to +13# draw weight for the button. Easton charts are notorious for 2 or more spine weights stiff on the big chart. Suprisingly, the youth charts are pretty close and don't agree with the big chart.....you'd think Easton would catch this, but I've heard (rumor) that it was two different people that made the charts. If or when you get a scale, measure the weight of all the componets you have on the tail end of the shaft..... it make a difference on the point weight needed. Play around with the values.....on a light arrow, it's almost a 2 to 1 ratio. Keep the strike plate position between the -1/16" and -1/8".....no more than half the diameter of your arrow. The closer you get to point on center with the plunger adjustment, the more sensitive everything becomes to form changes. The same holds true with too far to the left of center as you approach 0" on the value. 
Here is a screen shot.......








To make the 100 grain tips, melt solder inside the nibb tip or use lead shot and epoxy. For a standard clicker, keep your arrow length the same as or +1/4" longer than your draw length. If you get some extensions for your clicker, you can extend that to 1/2" longer.


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## leschrader (Jun 26, 2012)

Another option is to run standard points, not nibbs, at 85 grains.....makes for a lighter arrow. You would have no "footing" and "dynamically" a longer shaft. You would increase the weight the same way, with solder or lead shot and epoxy. (63 gr increased to 85 gr) When you run heavier weight tips (over 100gr) in the lighter arrows, to compensate for an over stiff spine weight, tuning becomes "touchy". Any error in form or draw amplifies.....the arrow tunes or works, but becomes inconsistent. The same applies to strike plate or plunger position......for a "forgiving" setup, try to keep things at a "happy medium" or middle of the range.


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## Cephas (Sep 7, 2010)

Anyone know the equivalent 8125/8190/X strand counts in relation to the fast flight on the spreadsheet or where to find that out?


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## leschrader (Jun 26, 2012)

Cephas,
I think that the major difference is between the Dacron used on the older recurves and the newer style low stretch materials. That makes a lot of difference. I'm using 8125G and using the same strand count as "fastflight" for use in the program....seems to work OK. I haven't used 8190 yet, but I know that they use a higher strand count than 8125 or Angel. To get an equivalent, you might try looking on some of the bow string makers home pages to get an equivalent string count for a specific poundage bow. Strand count, serving size and length, nock points/kisser buttons will all make a difference, but ,within reason, not enough to put you out of the tunable range. This program is to get you in the tunable range to start and then after you get everything right, provide repeatable data for use on other arrow combinations. Every person has a different release, draw and bow/arrow componets......that is the reason for the "personal form factor". When I switched from Uukha limbs to Border Limbs I had to use a "personal form factor" number even though the draw weight, arrows, riser and sight were the same. The limbs had a different acceleration curve, so the arrows "dynamically" reacted differently. The arrows were tunable, but I had to shorten them or change the limb bolts slightly to get the bare shaft and fletched together. This program is a great learning tool....play with the componets, values and dimensions to see how they interact. It's an eye opener......and a lot cheaper than doing it the "old way". :wink:


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