Primitive Archer
Main Discussion Area => Bows => Topic started by: Don Case on March 10, 2014, 02:07:53 pm
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I read that you should never pull a bow past its final draw weight when tillering. Say I started out tillering a 90# bow and got halfway done and realized that I'm never going to be able to pull this. So I changed my mind and tillered it to 40#, have I overstressed the bow by pulling it to 90# before I changed my mind?
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In principle: yes. But remember that the bow doesn't 'know' what your intended draw weight was or is. It all has to do with your design. You should have designed a bow that was capable of taking the strain for a 90 pound bow. If you would (for instance) tiller it to draw 110 pounds, the design would be overstressed. Or it was overbuild, so your goal of 90# was possible, but just on the safe side for that particular design. If you suddenly lowered your goal from 90 pounds down to 40 pounds, the bow will be grossly overbuilt. You should make a bow with an intended draw weight of 40# instead of 90# a lot narrower and possibly shorter. However, if the bow has not taken any set from drawing it to 90# early in the tillering process, it is still perfectly fine to narrow the bow now, in order to create a new design that is meant for 40#. If you just thin down the limbs from 90 to 40 pounds, the bow will survive, but will be overbuild and hence shoot sluggish. Especially when the bow has already taken set.
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Yes, to some degree you have. However the extent of the damage will depend on the characteristics of the wood you are using. On some woods like hickory, oak, black locust and other extremely tension strong woods most of the damage will be in compression. By the time you remove enough wood to take it from 90 to 40 lbs, you will have removed the majority of the crushed belly wood. Even when considering narrowing the limbs to adjust your design to the lower draw weight. On other woods that are more balanced in tension and compression strength, the damage will be shared more with the tension side. That will result in more damage as a whole, because you won't be removing overstrained wood from the back of the bow. Just my .02. Josh
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Whoops....darksoul beat me to it. Lol! Josh
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Theoretical question so I will give a theoretical answer.
It will probably result in more stress and crushed belly fibers than what would be ideal. Will it still work to retiller a bow to a lighter draw? I say probably, although I would expect the 90lb/40lb bow to take a bit more set than one that was made without pulling past 40lb while tillering. A lot of it would probably depend on how far into tillering you got before making this decision.
Lots of variables here. Some woods are more resilient than others. In the end I would be prepared for compression issues like set and the possibility of chrysals. That being said, going from 90lb to 40lbs you are probably going to remove a whole lot of the wood that was potentially damaged by tillering to 90lbs. I suppose it depends on how deep these cells go. Hopefully the wood was strong enough in tension to handle the stress on the back.
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Im guessing most of, if not all of the 90# early worked wood will be long by the time the bow gets to 40#.
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What Josh said
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Depends if your wood along with the demensions could handle #90 in the first place. Then it would easily handle 40#
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What Bryce said. Pulling it to 90# is only an issue if that caused the belly to compress. If there was enough wood to handle it then it's not a problem. The rule of thumb that says to never pull a bow beyond it's desired draw weight during tillering so as to prevent set is meaningless. What is important is limb design and dimensions. The rule should really be "don't pull a bow past a point where it starts to take set and when it starts to take a set, remove more wood from the belly".
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Thanks guys
It's nice to get a bunch of answers that are in agreement. I believe I understand it now.
Don
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That whole theory is very blown out of proportion. It almost seems like a scare tactic. In practice, wood is not that delicate.
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Its kind of iffy to me if you make a bow that originally pulled 90 pounds and took no or very little set or string follow then it couldn't hurt to drop it to 40 pounds heck in my head if it can handle 90 pounds with little or no string follow then at 40 it should be absolutely nothing for it But then again if you make a ninety pound bow and it takes four inches of string follow well then it's not going to be very efficient at fourth pounds ..