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Short staves- draw length and draw weight trade off - Finished with pics
jameswoodmot:
Ok, I’m up to date on the volume thing.
Question stands about finding the sweet spot with draw length and draw weight.Or draw weight and limb volume, if that is another way to put it.
Increasing the draw length, I will have to decrease the limb volume to maintain a suitable volume to draw weight ratio. Which in turn means I will be continually decreasing the draw weight as the length increases
A bow with set length and width, I assume, will have an optimum where the draw length is long enough to have good power stoke and the draw weight is high enough to be storing a good amount of energy. Beyond experience and trial and error is there any way to calculate that optimum?
RyanY:
This is a good question. You could probably approximate this by drawing out some FD curves at varying draw lengths and poundage’s and seeing how energy storage compares. There’s probably a ratio where the draw length and draw weight can change proportionally to make equal energy storage at any given combination. My guess is that maximizing draw length is more important for transferring that energy storage efficiently.
superdav95:
Good questions. Good advise from sleek. I’ll throw this wrench in all this. I made two shorty bow. Both 45-50lbs. Both bendy d style Osage bows. Both from same tree. In fact both were narrow sister splits from same short stave. Both had same dimensions of 50”ntn about an 1” wide. Both had small steamed recurved tips. Both seemed to be good till it wasn’t. One took set and then exploded at 26”. The other one is great. Little to No set yet and plan to finish it up for a 26-28” draw. I’ll post some pics here of it when I get back to it. And if it survives. I have other pressing projects on the go. lol. My point is that sometime we can do everything right and the wood has other plans. I’m sure there are rule of thumb methods to follow when it comes to short bows and even bendy handle bows. That will give you more certainty moving forward. The other thing that can be done for shorter bows to extend their draw is sinew. If done right a little does the job of extending your draw length with a measure of safety.
sleek:
I kept records on all the short bows I made, then plotted them on a spreadsheet, and found they followed predictable patterns. I found a came up with a formula that works with them and have used that formula to design my flight bows, with good results. Recently I built a simple program that will give you the predicted set a bow will take based off its working limbs dimensions and its draw weight. Im hoping to attach that program to this site as part of this years upgrades. But im happy to help run some numbers for you if you like.
Edit: I forgot to add, the density if the wood is another plug in for the formula. But, you can go off the standard density for any wood on Google. The working limbs dimensions and its density will give you how much draw weight it can handle without set. The draw length is determined by the bend radius, so its thickness is not a factor.
Selfbowman:
This little bow is 52” long and bends in the handle. Made by Kenny Cartwright. 1-1/4” wide at fades 1” mid limb and slightly under 3/8” at tips. The bow is 40# @24”!! Impressive little bow. I ask Kenny how far it could be drawn. He told me I don’t know. He has about a 26 inch draw. The bow took very little set. This might mess with your theory sleek. Leave it to Cartwright to pull this off. The bow is Osage by the way. I would love to pull it to 26” with a flight arrow but have not had the opportunity yet. The bow weighs 11.9 oz
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