Wood elastic limit....

[jeb532]

Seems to me that the best way to keep from breaking a bow limb is to avoid exceeding its maximum allowable %elongation.  For red oak that appears to be 0.8%.  Makes it pretty simple to figure out the maximum you can draw a given limb length and thickness combination.  Working on a simple spreadsheet to figure this.  I'll post it when I'm finished.

Comments on this idea are appreciated.

[Dano]

Make about 100 board bows, aim for the same draw weight every time and put that info on a spreadsheet and we'll talk. Course the boards would have to be from the same tree.   :D

[bjhaug]

Put the physics into compound bows.  Even holding all things consistent, it's too hard to say.  Just listen to the guys on here that have been doing it just as long as you've been an engineer - they know from experience, not from spreadsheets.

[Pat B]

A good generalization would be don't draw your selfbow more than 1/2 it's length(in a perfect world). An old saying...a bow fully drawn is 9/10th broken. I like to add 10% to 20% to my draw length and double that for a bow length.

[DCM]

Nothing at all wrong with the idea.  But estimating the working properties of a particular specimen can be difficult to impossible without testing.  What you see printed is at best a rough average, frequently just a test of one specimen.  What bowyers have found is that wood can vary as much between specimens as between species.

[jeb532]

Thanks for your comments!  Especially like the generalization that "a bow fully drawn is 9/10ths broken"...otherwise you are carrying around extra mass for no good reason...

[jeb532]

How do I paste a spreadsheet into this forum?