Sneak peak.

[Selfbowman]

Mark my cross section looks like Steve first cross section on the thread. The cross section kept the same ratio in diminishing mass .I trapped the bow before I started the tiller. Some fine adjustment on the traps after.

[mmattockx]

Fade to mid limb.

Now that's interesting. The straight width taper pyramid profile will overstress the outer mid part of the limb (~2/3 of the way from fade to tip) if the thickness is kept constant as most people say to do with the pyramid shape. To maintain constant thickness from fade to tip the limb sides need to be curved out a bit from straight to keep the strain the same all along.

Did you want to go with the same 1-1/8" width out of the fades or try a bit wider this time?


Mark

[avcase]

Well the bow came in at 20.9 oz. 50@27 shot one arrow between 220-230 several times. Shot a 500 gr arrow 200 plus. It lost half of the reflex from fade to mid limb in set. Good bow. May need to do a stretch test on this bow.

Hello Arvin,
I just read through the 8+ pages of this bow build and have some questions. According to the statement above, you initially shot a 10 ggp arrow over 200 fps with the bow drawn 27”?  The 27” draw is measured from the bow back or belly?  Next, you narrowed the tips some amount, the bow started taking some set and then the speed dropped to 169 fps with a 497 grain arrow. This is drawn the same 27”? Do I have this right?

Was the draw weight with the 169 fps shot less than with the 50# draw weight measured for the initial 200+ fps shot?  Of course, draw weight changes will effectively change the grains per pound for the 169 fps shot compared to the initial shot. Thanks!

Alan

[Selfbowman]

Alan the bow never shot 200fps! It shot 500 grain over 200 yds.  The arrow that shot 220 -230 several time’s weighed 460 gr. When I took more mass off the ends it did not do as  good at 28” the set killed the bow. I always measure to the back of the bow.

[avcase]

Thanks Arvin. I misunderstood that you were talking about yards, not feet per second!  Ha!
Alan

[Selfbowman]

Fade to mid limb.

Now that's interesting. The straight width taper pyramid profile will overstress the outer mid part of the limb (~2/3 of the way from fade to tip) if the thickness is kept constant as most people say to do with the pyramid shape. To maintain constant thickness from fade to tip the limb sides need to be curved out a bit from straight to keep the strain the same all along.

Did you want to go with the same 1-1/8" width out of the fades or try a bit wider this time?


Mark

Two inches from handle 11/16”mid limb 9-1/6. 2” from tip 9-16”

[Selfbowman]

The new handle glue up worked out fine.

[Selfbowman]

I peeled a bit more weight off this bow cause I like shooting it. This bow took more set than sneak peek  two the wiggle bow. I think it failed in tension due to the trapping. Can’t prove it though. Arvin

[Bob Barnes]

This should be your 3D bow!   

[Selfbowman]

Here they are together

[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.   

[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