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Sneak peak.
mmattockx:
Arvin,
I haven't forgot about doing a bow layout for you, I've just been too busy to sit down and do it. I'm also still trying to figure out the best way to post the output when it's done.
Mark
mmattockx:
All right, Arvin. Attached are (hopefully) 2 pdf files of your requested bow. One shows a crappy graphic of the back and side profiles with dimensions in millimetres and the other is a spreadsheet giving the actual dimensions in millimetres and inches. This assumes the same modulus of elasticity as the samples you sent to Alan Case for bend testing a while back, so you may need to tweak the thickness a touch to hit draw weight if this piece of wood has a different stiffness than the test pieces.
The design is 67", nock to nock. Draw weight target is 50lb @ 28". It is a touch wider than 1-1/8" at the fades with the grip area 1" wide x 1-1/2" thick. The limbs are assumed to be rectangular in cross section, to the dimensions given. Don't round the corners much or you will screw up the design. I round the corners no more than maybe 0.1" (at most) on my bows and they have been fine with that.
The bow is designed using David Dewey's spreadsheet which I have found to be very close to my real world results so far. I think it gets you as close as you will find to the perfect diminishing mass as you travel along the limb to the tip. The spreadsheet only works for flat bows, so if you recurve the tips much it will throw things off and possibly overstress the outer limbs where they blend into the tips. You will be better off to reflex the whole limb in a smooth curve from fade to nock if you insist on adding any reflex. For it to work you must stay very close to the dimensions given. The last bow I made this way I found I could get within 0.002-0.003" on thickness and +/-0.010" on width and that worked.
One thing to note that is not obvious, the sides of the limbs are not a straight pyramid taper, they are bowed outwards a bit. This is correct and not wrong. A straight pyramid with constant thickness will overstress the outer-mid portion of the limbs. The limb needs this width profile to provide truly equal strains over the full limb length.
Mark
Bob Barnes:
mmattockx... Thank you. I know that Arvin has worked hard on this and your calculations will help him get closer to his perfect flight bow. You two are amazing. :OK
George Tsoukalas:
Arvin, I think your bow has a great profile and the chrono reading I saw seems right on.
Your bow making skills are incredible.
Thanks for sharing.
Jawge
bjrogg:
Nice bows Arvin.
I always assumed that the set was from compression, but you really got me thinking about it.
I’m starting to think you might be right about stretching in tension and developing set.
My HHB seems to take more set than my Osage.
It never shows any signs of frets on the belly. Still shoots fine but whenever I get set it always annoys me.
Maybe I should try trapping the belly?
Bjrogg
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