Primitive Archer
Main Discussion Area => Bows => Topic started by: DC on June 15, 2015, 09:31:34 pm
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Has anyone seen a chart or something that will tell me how much to change the spine of an arrow depending on how much the arrow pass is offset from center shot? I've seen mention of arrow length and tip weight but not offset.
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I don't know of a chart, but I have a solution for you. Take a stiff arrow and start sanding the middle a little at a time shooting it in between. When it shoots good out of the bow in question, test the spine. Write down your results for every bow you do this with and you'll find out the formula pretty quickly.
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DK, I'm not sure if you are following what I'm on about. If I was to do it myself I would start with a centershot bow and build up the arrow pass a bit at a time keeping track of the spine of the arrows that shoot well.
Anyway, I'm kind of surprised at the lack of response. I have a 37# bow with six arrows (42#with 125gr tip and 3" too long)that shoot nice and straight. I made a new bow that was about 32#. I tried the six arrows in it and they didn't shoot well at all. I ran my test arrows through the new bow and discovered the this bow wanted 30-35# arrows. I rummaged through my stash of arrows and found 5 34# 125gr 3" long arrows. They shoot great. So the bow went down 5# and the arrows had to go down 10# to work. Tip weight and length were the same. The only thing I can see is that the pass offset(if that's the right term) increased some. Is there something else I should be considering?
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None of that garbage matters with self bows. Two identical self bows, aren't. Find arrows that shoot well from each bow you own and don't ask why, just enjoy.
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I can see your reasoning and it is probably less work to do it your way but I'm one of those guys that just has to understand how things work. I just assumed that if someone has gone to the trouble of figuring out that an extra inch is worth 5# or whatever that someone would have worked this out. I guess the problem of string alignment and how to measure it enters into this. It just takes a few minutes to shoot my test arrows and determine the needed spine. I'll just be happy with that, I guess :) But if anyone sees an article about offset be sure to let me know. :D
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I like to know how things work as much as you do, that's why I said forget about a formula.
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If you find it out let us know. I've been doing this stuff for about 30 years and never heard of anything like that. I do as Pearlie suggested.
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The glass guys have a great formula that does just as you want. But again, none of that translates simply because we aren't dealing with dead nutz symmetrical bows the repeat themselves over and over and over.
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Even the glass guys end up using trial and error with fiddling with tip weight and shelf build up etc.
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Thanks for the input guys. I need my butt kicked back onto the path occasionally :)
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google "stu millers spine calculator" I use it all the time to get me in the ballpark. I have read a lot here lately suggesting sanding to adjust spine, but I do that by changing point weight. I sort of disagree (respectfully) with pearly- this stuff matters with self bows just as much as any other bow. The formulas involved can be difficult to apply because self bows are difficult to measure for the centershot measurement, but using the above program can take a lot of the guess work out- leaving you to tinker with the fine tuning. As others have said, trial and error is a good way, but the program can get you in the ballpark.
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Pearlie didn't say it didn't matter.
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He said "none of that garbage matters with selfbows"
perhaps I am misinterpreting what he meant. I thought this meant that you shouldn't bother measuring the arrowpass width of a selfbow because selfbows do not behave predictabilly based on this measurement.
I understand that selfbows do not lend themselves to being measured for arrow pass width, but I personally have good luck using spine calculators to get my arrows flying well.
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I have a tendency to assume. That's my fault. What I meant was every single self bow is different no matter their similarities in measurements.
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Ok, thanks for the clarification. I value your opinion greatly.
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If it helps any....with glass bows (Hill style in particular), I generally deduct 5# of spine for each 1/8" a bow is cut proud of center when calculating spine for wood arrows. My experience with the three self bows I have hasn't been but for a few months, but like Pearl said.....each one seems to have its' own likes for spine and point weight.
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None of that garbage matters with self bows. Two identical self bows, aren't. Find arrows that shoot well from each bow you own and don't ask why, just enjoy.
Basically this is what I try to achieve is build all bows at around 40-50# use the same arrows spined between 40-45 some bows are better than others. Most of this boils down to one thing my shooting ability, its getting better and I know I will never be a super star, I just enjoy. :) On the other hand some arrows are wonky from the get go. >:D therefore garbage.
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I have 3 Selfmade osage selfbows, all of the same basic dimensions, all within 1/2lb of draw weight to each other,(50#@28"). I cannot seem to shoot the same wood arrow off each of these bows without making some adjustment to the arrows. I prefer to alter the shaft length and leave point weight the same. I assume very minor tiller/timing difference in each bow to be the cause. Maybe difference in physical properties of the wood itself, growth ring thickness, early to late growth ring ratio, who knows. But I think any formula, would still only be an educated guess, and then would have to fine tune arrow to individual bow from there. JMHO. Brian