D section limbs

[upstatenybowyer]

Just wondering under what circumstances a bow stands to benefit from D section limbs. Thoughts?

[PatM]

Continuous war.

[FilipT]

And so it begins...

[upstatenybowyer]

Uh oh. I hope I didn't open Pandora's box with this one.  It's just that I noticed Marc (whose work I greatly admire) often employs shallow D section limbs.

[Marc St Louis]

I think Pat is being overly dramatic  . 

D section limb are best used with wood elastic in compression and are very useful in taking strain off the back.  This is good for a higher stress design since the elastic belly wood works harder giving the back a "break" in the workload  .

[PatM]

Overly sarcastic.

[George Tsoukalas]

The English war bow came about because with the longer, narrower bow you could get  more bows from a tree. The rounded limbs mean you can turn them out faster.

Marc, sounds good but most woods are stronger in tension than compression. So specifically what woods are you talking about?

Jawge

[Selfbowman]

I build primarly Osage but D comes in to play usually when my stave is on the thin side. They seam to take a bit more set but has good cast from the limb being long and narrow. Most are not completely D in design. The belly is still flat some what in the mid limb section. Yes they do seam easier to tiller. Arvin

[FilipT]

I heard that osage in longbow "D" configuration (more rectangle then D) produces handshock, is it true?

[Marc St Louis]

George
Wood is stronger in tension but all that means is that it resists stretching more than it resists compressing.  That has nothing to do with the wood's elasticity.  A wood can be elastic and strong in tension and a bow made from that wood will not likely fail in tension and/or it will make a great backing material.  A wood that is elastic in compression will resist cellular compression failures (chrysals)

You've been making bows for quite awhile now so you should know which wood species are elastic but just in case here are some.  Yew, Osage, ERC, HHB, those are some of the better NA species

[Dances with squirrels]

I have YET to make a wooden bow with a flat belly, and have no plans to. My bows range from deep D cross section in English longbows, through the spectrum, to a squashed, yet fully radiused belly on woods that aren't nearly as elastic in compression. That said, three of those four Marc mentioned are #1, 2, & 3 of my favorite three bow woods. Coincidence probably 

[Stick Bender]

I know Dean Torges in his book Hunting with the osage bow is a big fan of the radius belly & goes into some detail about it , when I get my tillering skills better I would like to try one , I read that there saposed to easer to tiller.

[upstatenybowyer]

This has been very informative to say the least. Lots to sublimate. Thanks to everyone for your input. 

[George Tsoukalas]

Yes, Marc, I do know which woods are considered to be elastic.
I've read TBB 1
I meant to ask which woods do you prefer for your particular design- rounded belly, high stressed..
Jawge

[Marc St Louis]

Yes George I've also read TBB 1 but experience has been a  better teacher 

When talking backed bows then I prefer Yew and Osage in that order with ERC not far behind then HHB.  I would change that order and put HHB before ERC for selfbows and add top grade Elm to the list next to HHB.  Heat-treating adds another dimension to this altogether since that increases the compression strength of wood thereby increasing the stress to the back, doesn't increase the elasticity of the wood though.