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Stress and performance
Selfbowman:
Guys you know I’ve built the same bow design for years because it works well for me.and yes by doing so I’ve played with moving mass to accommodate for set. I was told I was wasting my time. That made me laugh because I was still getting set. But that being said my bows have 1-1/2-3” of reflex in my he last ten inches of the limb. Causing more stress fade to mid limb. So I made that area wider and by adding the mass it cut down on set. If you use your calculations for n a straight limb bow it will be different from say my design. I don’t know how to estimate the added mass needed to prevent the set . Deflex in the handle can balance the stress load more evenly but that’s another can of worms. The more early draw the faster the bow. Think compound for a moment. This is why I think the farther the tips in front of the bow handle with the same set the faster the bow will be! That requires more width fades to mid limb. Short or long bow. Just an opinion.
willie:
--- Quote from: Selfbowman on May 15, 2024, 06:46:33 pm ---That requires more width fades to mid limb. Short or long bow. Just an opinion.
--- End quote ---
adding width to limit set certiany seems like you can get a good handle on how much extra width it takes to make your design shoot better.
does your width out of the handle run straight for a ways before you begin to taper? if so, have you changed the distance out the limb before the taper starts? or just go a little wider to the same point as before?
Selfbowman:
Willie the best bow shots that I have gotten with broadhead arrows was with a straight taper bow 2-3/8” at fades to 1/4” at the tips. I have taken it parallel for 9” then @18” 1-1/4 wide and then to narrow tips. All with the same reflex. This is with Osage . I think the parallel for nine inches is working better but still testing. On a 28” working limb design it’s putting plenty of stress on the limbs especially the inner limbs. I am considering going to 2-3/4 at fades . It might overbuild it though.
Aussie Yeoman:
In Archery: The Tecnical Side Hickman showed that the ideal width profile for circular tiller is not straight line taper in width as we consider the classic 'pyramid' bow, but ever so slightly bulged near the flares/fades. I've found, when making pyramid bows with circular tiller, that running the limbs parallel width for 4-5 inches before tapering in straight lines to be a good-enough approximation for ease and speed of layout.
mmattockx:
Badger also mentioned keeping width parallel out of the fades for 2-3" and I have used that as well. It does a great job of evening the stresses out right at the end of the fade into the working limb portion. There tends to be a bit of a stress concentration right at that point and a short parallel section smooths that out.
A second thing not mentioned yet is that the theoretical pyramid shape tapers to a sharp point at the nocks. Since this is impossible in reality the way around it is to layout the pyramid taper to a sharp point, then draw a short parallel width lever section from the nock to where it intercepts the pyramid taper. This can be as narrow as you think you can make it. On my last lam bow I think that lever is about 5/16" wide for something like 6". I was worried about that being fragile and maybe unstable but it has not proven to be so.
If you straight taper to the nocks with some width at the nock then it tends to overstress the middle of the limb a bit and you need to taper the thickness in the outer half of the limbs to balance that off.
Mark
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