Main Discussion Area > Flight Bows
Arvins 62" osage design
willie:
that thickness should be enough, maybe too much ,but I would not do any thickness reductions anytime soon.
the program has no way to account for any loss or addition of stiffness if we heat bend the wood or heat treat to set a bend. being too thick out there in the non bending section is not going to change the limb design elsewhere on the limb appreciably, so leaving it "as is" will be good.
maybe you typically set the bend with a scorching heat treat with most bows?, but maybe not doing that right away would be a good idea if you want to increase the bend later in the build.
taking any excess mass off the tip to reach a final highest possible arrow speed should be the last thing done, after (or before?) the hotter? heat treat to set the final bend.
just to get ahead of ourselves, I will see what a 3" hook does to the design as it stands >:D
willie:
to anwser Arvins earlier question about what happens if we make the outers work less and become more like levers, I adjusted the model. and might have to change my earlier opinion.
Directly below is the stress plot shown earlier with more bendy outers, and below it is the stress plot for the same design with stiffer outers. the stress increased 1/2 of 1% but the arrow speed went up from 222 to 236. quite an improvement for a modest increase in stress.
The difference is not easy to see at a glance, but a careful inspection arount the 24" mark will show less stress (and bending) and a straighter slope to the nock.
willie:
bending the recurve to 3" behind the handle from the 1.5" in the previous improved design raised the stress and increased the poundage from 50.9 to 55.9. But Arvin needs to stay at or below 50# to stay in the class.
Taking a few scrapes to bring it down to 50.1# and yields a bow with 10% more stress than the 1.5" recurve and the arrowspeed increases from 236 to ummmm... 229.
there could be any number of explanations. off the top of my head is
I am not doing something consistently with my models
I need to input a more realistic wood density
something with the new string angle is not helping
the tips are too thick and hence too heavy.
below is the stress plot for the 3" recurve and the arrow velocity during the powerstroke for both recurves.
the 190 gr arrow shot with the smaller recurve seems to leave the string sooner and comes up to speed quicker.
note how at the point of the highest velocity the curve seems to go flatter. this would be consistent with the observation that its hard to eek the last few fps out of a light arrow, and there are considerations that the program does not account for in addition to hoping the program for arrow velocity dynamics is accurate at the edge of the envelope. interesting to play with tho.
Selfbowman:
Willie try a 150 gr arrow though the new design please.Willie I’m curious about if the design has a specific need for a certain weight of arrow to have the most speed from the bow. It would be a pain probably to do but try 140-200 gr arrows through the design . Any design. Do it in 10 gr increments to see at what weight the arrow needs to be the most efficient. Please explain to me in simple terms if this would or would not be useful.
Selfbowman:
I’ve been using my trusty contour gauge and I have all 4” increments the same on both ends of the bow. Well the one right at the fades have a slight difference. All the rest match. So if I can get the thickness from each 4” increment right we should be good to go.
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