Primitive Archer
Main Discussion Area => Bows => Topic started by: ssrhythm on February 13, 2023, 04:52:28 pm
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What poundage gain can you expect per inch of bow length reduction? I can not find my TBB with that info in it...my house is a wreck and in need of a major spring cleaning!
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ohhhh... i cant remember for sure... but I believe for every inch you pike, it gains 5#. Just make sure you don't lose the 5# retillering! that's what happened to me ;)
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you can tie a nock where you gonna pike and see,,
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Very little on most bows. 1-3# per inch per limb. Generally you have to scratch a bit on the limb you shortened to get the tiller back in tune, that takes away a majority of your gain.
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About 5# which may be offset by more set. Jawge
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Thanks for the replies. See my "redoing my trade bow" thread above to understand why I asked this question in the first place.
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What Pearl said
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well ok, its not always a wash,, if the bow is too long,,and mass weight is too much,, making it shorter can raise the draw weight and also make it more effecient,, dont make me go back and post notes ,, from chronograph testing,, I have had good results and not so good results,,so it depends on the starting point,,
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well ok I found my notes not as exact as I like but from 1997,,,was using chrono then,,
then main flaw, i didnt note how long the bow was,,
it was 50# at 27 and shooting a 424 grain arrow 154fps, im sure it was a heavy b5o string,,
I cut the bow to 67 inches and it was 61#@ 27 inches,,
it would shoot the same arrow 176 fps,,
Im pretty sure the bow was 70 inches or so and had horn nocks,, so not only did I increase draw weight but reduced mass the tips as well,,
I dont have notes on the failures,, (-S
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well ok I found my notes not as exact as I like but from 1997,,,was using chrono then,,
then main flaw, i didnt note how long the bow was,,
it was 50# at 27 and shooting a 424 grain arrow 154fps, im sure it was a heavy b5o string,,
I cut the bow to 67 inches and it was 61#@ 27 inches,,
it would shoot the same arrow 176 fps,,
Im pretty sure the bow was 70 inches or so and had horn nocks,, so not only did I increase draw weight but reduced mass the tips as well,,
I dont have notes on the failures,, (-S
Yes Brad I try to forget the failures after I learn my lesson.🤠
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Jim Hamm, of eternal memory, gave a formula in TBB 1.
If I remember correctly, it worked out to about 5# provided 1 inch is taken off each limb. He accounted for several factors.
It's too late for me to go searching. By now most bowyers have TBB 1 anyway.
Jawge
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The bow was definitely too long and was well below max efficiency. I started making it for a very tall friend of mine and figured a longer bow would work out for him. It turned into my trade bow when my trade bow popped and time became an issue. I turned it into a pretty nice shooting selfbow that was very easy to shoot very accurately. It had a tough more hand shock that I was happy with, but it was a shooter. It started ticking the last session of shooting and arrow tuning I did before I was going to ship it.
It was 59# @28” and 67” tip to tip. My plan is to chase the next growth ring removing the compromised back. I’m hoping the weight reduction there will be a wash with improved efficiency and increased draw weight once I remove 2.5-3 inches from each tip, recurve the bow, and sinew back it.
If I end up with a 48# @ 28” or higher 62” sinew backed recurve, I’ll be very happy. I don’t know how much taking it down to the next ring is going to drop the draw weight, but if I gain ~ 15 lbs by taking off 3” per limb and a few pounds with a greater degree of recurve and a few lbs by the reflex the sinew should induce, I think it could work out……if I get really lucky.
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I have had good luck over the years piking them, usually about 3 lbs per inch and if the tiller was good to start with it usually don't change it much, don't do it as much as I use to, gotten better at hitting weight but it has always been an option if the bow was long enough to accommodate the draw length I wanted. :) very minimum for me is double the draw length i want and add in non moving part/handle and fads.
Pappy
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TBB 1 P. 283
Basically, 3/4" from each tip will raise the weight from 52# to 58#.
Jawge
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can u just sinew over the back as is,, more details and pics please
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Not sure Brad. I’ve never sinewed over a cracked back, and I don’t want to waste the time and sinew for it to just break anyway. The bow was too long to begin with…for a sinew backed recurve, it is way, way too long. I’m aiming for 60-62 inches, so I think I’ll be gaining enough weight to just eliminate the compromised back.
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how do you know the crack is only one growth ring
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show me a pic of crack,, so I am not just guessing
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Assuming you can consider the bow limb as a lever and the handle as the fulcrum, halving the bow in length should double the draw weight, Archimedes already provided a geometrical proof of this principle thousands of years ago.
So from that it's easy to calculate from the initial length and draw weight, and the intended draw weight the length required to get to that draw weight.
Or you can reverse it (how much do I gain from shortening X amount?)
I could send a spreadsheet with the details, you just have to copy the three values (length, current draw weight, intended draw weight) and it will output the desired bow length.
There are a few additional underlying assumptions, but in general this works pretty well.
For example, if your current bow is 65" and draws 45#, and you want to get to 50#, the new length should be 61.7", assuming the bow can take the extra strain.
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or you could tie nocks at 61 and test before you cut,,
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Great ideas and points to try and consider. Bow is a scosh shy of 67” as is. I’ll try to post a pic tomorrow. I can’t be sure it’s only in the top growth ring, but I think it is. I worried about pulling it enough yo get good glue under it, but superstition CA would probably get in there. If it’s into the next ring, I’ll probably shorten it more and make It my son’s new bow and just start another for Mo. We are finally getting some decent temps to get out and do something with it starting tomorrow. Thanks for all the input.
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what caused the crack, how big is it etc,,
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I just piked a 72" bow to 70". Gained 3#. It took a slight reflex out of it. It´s now straight, so it was a slight trade off but I think it was worth it.
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You can always add reflex back into the bow with heat.
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Pat, I guess I could but it´s a reflexed kink on only one limb on a Mollegabet bow I´m working on, right on the fade where the limb transitions from bending to stiff outer limb, so I´m fine with it looking less wonky now.