3Rivers Spine Calculator Center Shot Measurement

[Cng]

Hey, guys. I have a stupid question that I can’t find answered anywhere online. I’ve read a bunch of threads on how people measure their center shot on their bows, and I’ve read a bunch of threads about people’s experience with the 3 Rivers Spine Calculator…

But no matter what I Google, I can’t find anyone mention specifically what you are supposed to enter in the “center shot” field on the calculator. Are you supposed to enter the riser cut (i.e., how far past center the riser is cut), or are you supposed to measure what your current center shot is set to… or perhaps you’re supposed to enter what you WANT your center shot to be?

I tried the first option, and it’s showing pretty weak for my current arrows, but the second option shows pretty stiff. And it seems weird to enter the center shot of your current setup or just arbitrarily pick what you want your center shot to be when that seems (at least to me) completely dependent on how the arrow tunes.

What am I missing here? I’m sure it’s something stupid obvious.

FYI, I have a field tip test kit, and I intend to buy bare shafts to play with, but I’m just messing around with some different options in the calculator, and I would like to know that I’m entering everything correctly for my current setup so that I can figure out my “Personal Form Calibration” number. Center shot is the only thing that I’m not sure is correct.

 

[Cng]

Here’s 3Rivers instructions. The first part makes it sound like you’re just measuring the cut of the riser… but then it mentions the strike plate/rest and says “that part comes later,” when, as far as I’m aware, you never enter your strike plate/ rest setting anywhere.

From 3 Rivers:
How deep cut in the arrow shelf is on the riser. Measure (in inches) the width of the riser at its thickest point (right below arrow shelf cut-in). Then, measure (in inches) the depth of the arrow shelf not including strike plate (arrow rest), that comes later. Divide the overall width by two, then subtract shelf measurement. If a negative number your bow is cut past center. Choose from dropdown selection. If inbetween size, go deeper cut and add on to strike plate thickness the difference.

 

[Boxerboxer]

You're overthinking it. "That comes later" just refers to the fact that there's a separate field to enter strike plate thickness which is entered after the center cut. If you're trying to look at your current setup, just measure your bow according to the instructions. When you select "yes" for "Has Strike Plate" it gives you a spot to enter a thickness.

 

[Cng]

"That comes later" just refers to the fact that there's a separate field to enter strike plate thickness which is entered after the center cut.

Ah! I think this has been my whole problem! My bow is not in their list, so I've been checking the "generic recurve" option, and apparently the "strike plate thickness" option does not exist for generic recurves. Odd...

 

[Wrench]

What's your setup? Someone may be able to help narrow the gap.

If not, start long and heavy or stiff and light....then shoot and correct based on dynamic results.

 

[oldgoat]

And remember this, with all these calculators, if you put garbage in, you are going to get garbage out! Try to be accurate as possible!

 

[Cng]

Yeah, for sure. That’s why I’m trying to make sure I get this right. All my other info is measured, weighed, and verified. I know I’m going to need to enter a personal form calibration number, but if its based on an incorrect center shot, it will screw up everything.

I'm currently shooting an old Hoyt Dorado riser with a springy rest. I have a 32+” draw, so I don’t generally have the luxury of cutting shafts. I usually buy 33-34” shafts and add weight till it tunes. But I was hoping to try to hit a certain tip weight on my next arrows, so hence the calculator…

After reading @Boxerboxer 's response and realizing I was missing out on the "Strike Plate Thickness" option when I select “Generic Recurve,” I’m getting the most accurate results for my current setup by following 3Rivers’ instructions for measuring center shot, but instead of measuring the arrow shelf without the strike plate/rest, I measured it with it, as though that’s just set center shot of the bow’s riser. Makes a lot more sense than what I was thinking before, and I feel dumb for not having clicked on any of the other bows to see that they had that option! I just assumed they all had the same input options.

I'm going to do some additional testing with a different spine shaft and see how close the calculator comes to it.

Thanks for your all’s comments, and sorry for the dumb question!

 

[Beendare]

Thats the Stu Miller calculator …and there is better instructions on that download site.
I use a measuring tape held against my strike then sight down the string when held dead center.

BTW, that calculator nailed what tunes perfect in my 64” ILF

 

[Cng]

Thats the Stu Miller calculator …and there is better instructions on that download site.
I use a measuring tape held against my strike then sight down the string when held dead center.

BTW, that calculator nailed what tunes perfect in my 64” ILF

First I've heard of the Stu Miller Calculator. I'll definitely check it out. Thanks!

 

[bobinmi]

The stu miller calculator is fantastic and I believe that 3rivers bought one of his generations of the calculator for theirs. I think the real benefit of the system is once you have an arrow of any type tuned to the bow. you can plug things in and adjust the form factor until its dead on. Then you can see what other combinations get you to the same place.