(...) in one little area that doesn't seem to be spreading, the fiberglass has lifted from the bow. Looks like it just didn't have enough contact, or it pulled loose material up.
Now I see ERC's and black walnuts with NO backing at all?? help me out fellas, do I need a backing on my sap wood bows and my soft wood bows (maple)? I'd like them to last a little while.
IF you glue any type of backing (f!b€rgl@$$, rawhide, sinew, wood, linen cloth etc.) onto a stave bow, you need to remove all cambium and inner bark, and apply the backing directly onto the wood. Cambium is not so tightly attached to the wood, generally speaking, so it's very understandable that the backing will peel off from the wood, taking the cambium with it.
There is a difference between "softwood" and "soft wood". Mind the space! Eastern red cedar (ERC), yew and pine are all softwoods: woods from needle leaf trees. Any wood from a broadleaf tree species is considered a "hardwood". The terms softwood and hardwood have nothing to do with the hardness of the wood! High ringcount yew is a softwood with hard wood, while balsa wood is a hardwood with soft wood. Maple is a hardwood with hard wood. Although there is also soft maple (such as red and silver maple) which is a rather softish hardwood. To add to that, not all wood species have sapwood and heartwood. Walnut, yew and ERC do indeed have clearly visible sapwood and heartwood. But maple (and also ash and hickory, to name a few) don't have heartwood. It's all sapwood, while old trees might form a dark heart, which is 'false heartwood'.
So when do you need a backing? It has nothing to do with the wood being soft, or the wood species being a softwood, or the bow having a sapwood back! The necessity for a backing is dictated with the tensile strength of the wood species (a mechanical property of the species), or by the grain pattern on the back of the stave/board. ERC has a fairly low tensile strength, while it has a very decent compression strength and excellent elasticity (inherent properties of the wood species). As such, a bow will likely fail in tension (=on the back) before it fails in compression (=on the belly). A backing is therefore a smart choice, since it elevates the tensile strength of the bow.
The wood species ash generally has a high tensile strength and a decent compression strength. It would not need a backing, based on the mechanical properties of the wood species, yet we see backed ash bows every now and again. That is usually done when the back of the bow is compromised, when it does not show the best properties for a highest tensile strength configuration. That is the case when the grain is violated, such as in a board that is not straight grained.
Black walnut and ERC are both wood species with a pretty low tensile strength and they are generally backed. However, the backing is not necessary, and a skilled bowyer can easily make a selfbow (without backing). When the back is as strong as possible, the tensile strength can still be enough. The back must be straight grained, with no violations, and the design of the bow must be adequate to handle the tensile forces. For a beginner, this may not be as easy as it sounds. A backing is then a smarter idea, since it adds a lot of security to the bow.
