Center shot measurement

[Armoured_Saint]

I'm attempting to use a spine calculator to help me get a ballpark on some new arrows, but I don't know what the centershot of my longbow is. How do I measure this? The riser is about 1 1/4" wide and the shelf is cut about 3/8 to 1/2 into it.

[Bladepeek]

I've had pretty good luck putting a piece of masking tape on the back. Measure and mark the center of the limbs at the widest points above and below the shelf and draw a line connecting the dots. It's fairly easy to measure from this center line to the shelf cut.

[Prairie Drifter]

I measure the 1: width at the fades w/ a caliper. Divide by 2. 2: Measure the sideplate where the arrow sits against it. If the measurement is less than the first, that's how far it's cut past center. IE; #1= .75 #2 = .625. Difference is .125 convert to fraction, 1/8" past center.

If the second measurement is larger than #1, the difference is + center.

Hope this helps

[Bjorn]

I measure like described above if contacting the bowyer is not an alternative.

[Armoured_Saint]

So in the spine calculator -## would be past center and positive would be the opposite. Correct?

[Bladepeek]

Prairie Drifter, that assumes the "off" side of the grip is the same distance from center as the edge of the fades. That's not the case on all of my bows. That's the only reason I went through the exercise I mentioned. If they are the same, then your way is a lot easier.

Ron

[Prairie Drifter]

Originally posted by Bladepeek:
Prairie Drifter, that assumes the "off" side of the grip is the same distance from center as the edge of the fades. That's not the case on all of my bows. That's the only reason I went through the exercise I mentioned. If they are the same, then your way is a lot easier.

Ron

I'm not quite sure what you mean, which bow are you talking about?

[Bladepeek]

I have several bows which are widest at the fades, but the handle section of the riser and the window are not symmetrical. The sketch here is obviously not drawn to scale, but I think you can see what I mean. The limbs (again hypothetical measurements)are 2" wide at the fades. Half of that gives me 1" to center.

If I measure 1" from the outside of the riser to the cutout and get 3/4", that would mean that I have - 1/4" cutout, when it is actually center.

[Prairie Drifter]

Oh, OK now I know what you mean.

[bowhuntingrn]

Go here:  http://www.heilakka.com/stumiller/calculatorinstructions.pdf  see #12. Basically the same as above, with pictures and description from the man who designed the calculator.

[Bladepeek]

bowhuntingrn, I read those instructons when I first downloaded Stu's calculator. I think that is the last time I looked at them. It was good to read them again.

The instructions are so detailed for things like footing, cut to center, actual, measured draw length, etc. I have a hunch a lot of the dissatisfaction with the table stems from garbage data fed in. I have always found it to put me really close and then I bareshaft to fine tune.

Once I have a bareshaft flying just right I can crank in a personal form factor to get the numbers to match performance. From that point, I can change shaft length, point weight, footing, even shaft type, whatever I want and know I will be very, very close for that bow.

I am going to go through the instructions step-by-step, measuring again where "guestimates" were used and putting in correct numbers. Bet my personal form factor will seldom be anything other than  "0".

I still marvel at all the work Stu put into that chart and how well it really does work.

Thanks for sending me back to school  

[bowhuntingrn]

You're very welcome. I reference the page often just to make sure I get my measurements as close as possible. When the numbers I put in are accurate, I find it gets me very close and minimizes tuning time.