Tim says: A back is as stiff as it's least-stiff area. If the cable is not uniform in diameter the narrow less-stiff areas would seem to represent the net stiffness of the back, the thicker areas being partially dead weight. The thinner areas will be stretched farther than thicker areas, possibly to failure." Even though the thicker area are harder to stretch I need to determine if they actually are storing less energy per mass than the thinner areas. Intuition isn't dependable.
So, this I knew already from reading your stuff, etc. , and I believe it's totally accurate. Let me add that a sinew cable is usually made of multiple smaller strands in order to eliminate weak and thin spots in the same way multiple strands benefit a bowstring, for that very reason.
Tim Says: Even though the thicker area are harder to stretch I need to determine if they actually are storing less energy per mass than the thinner areas. Intuition isn't dependable.
Intuition is NOT dependable, true. But, since sinew is SO elastic in tension, I doubt it is analogous to, say, limb thickness. We know a thick limb even even a small amount stores a BUNCH of energy. I may be wrong, but it seems to me that energy storage through elastic stretching is more dependent on travel, but that any amount of stretch stores energy. This should be testable by snipping a wide rubber band slightly narrower in one spot. I do however believe strapping or anchoring a cable down in one or several spots can change everything.
If the spacer DOESN'T have to be light weight, why are we using the glue-soaked cotton and not some other material? Or am I missing the point entirely of your design?
Tim says: "Yes, if two slats of wood they must rigidly be keep from slipping in relation to each other. But this might not be absolutely the case if the back is sinew."
OK, but I'm fairly sure it needs to be anchored at least somewhat to the belly to maintain their positional relationship.
What I mean is, I'm imagining a paddle bow, backed with sinew which covers the whole face of the back. The sinew back is essentially the same front shape as the belly. Now, similar to your experiment here, we somehow lift the entire sinew back and add a "spacer".
IF the sinew backing now floats unsecured atop the spacers, bound to the belly only at the tips, or even tips and handle, it basically becomes a badly misshapen, flat cable, over-stressed where it is narrowest.
IF, however, we do what you did, using glue-soaked cotton, the cotton is glued to the belly and the sinew back is glued to the cotton, indirectly anchoring the back to the belly.
Am I understanding this correctly? Does the cotton serve any functions I'm not imagining, besides anchor and spacer?
Tim says: Imagine a semi-rigid spacer, rigid enough to prevent the narrow outer-limb sinew from stretching dangerously more than the wider gripward sinew, but flexible enough to not fail when drawn from large reflex to a full draw
That's essentially the case with this bamboo/cotton-glue/sinew test bow. Surely not optimum, but worth noting."
That answered my question......
BTW, I'm ok to argue, but I mean to feed you ideas and perspectives that may help you further develop the idea.
