Can someone clarify something for me? TBB1 says that the outside 10% of the thickness does 50% of the work so on a .500" thick limb .050" is doing 50%. So why does it matter if the boo is a little thick? If the outside is doing all the work isn't the rest of the boo just along for the ride? Why does it matter if that part is Yew or Bamboo?
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This is my understanding. It isn't that the backing is too thick, like theoretically or in principle. It's that IF the backing is very thick, that necessarily means the belly slat is thinner.
Early on in my bowmaking, I made a lot of bamboo backed boofloo and bamboo backed tropical hardwoods like ipe, jatoba, and bulletwood. I had fewer tools BTW, and frequently glued a 1/8" bamboo backing to a 5/8" or 3/4" thick piece of ipe or whatever AND forced it into a R/D posture. Number one, doing so was probably overstraining the belly slats glue surface in compression DURING glue-up, such that the glue line was a backing glued to over-compressed wood.
But number two, by the time I had worked the bow down from "construction beam" stiffness, I most often had a net limb thickness of 3/8" or less. Now I start with a 1/8" backing and glue on a pre-tapered 3/8" slat. BUT, imagine if you started with bamboo, say a highly crowned piece you want to be wide enough so you left almost 1/4" thick. Now your finished belly is only 1/8" thick. That' just not enough balance to hold the shape of the original form.
This is one benefit of tri-lams, BTW.
