You can only work with the wood you have so get that string tight along the back and draw out the bow as best you can. Try to get the knot in the centre or off one edge. You can always put a small localised waggle in the stave if the knot falls half on the the edge*. When in doubt just leave extra width, it can be taken off later. Extra width is less troublesom than extra thickness.
E.G if the knot falls off the edge and leaves a 1/42 nick out of the edge, just allow a 1/4" bulge out on the opposite edge. Tyr to respect the flow of the grain where you can.
Today I say a cheapo Hickory bow that had failed. Looking at the edge the grain dipped down and back up severely, but the bow had just been cut out with no attempt to allow for it... the back failed with a crack following the exact line of the dip.
I'm currently tillering a 95-100# Yew warbow on my blog, I've put up plenty of video clips and pictures, which will hopefully help you.
Del
