I have made a few multi-lam bows and I used 1/8" center lam and started with 1/8" belly lam that were reduced while tillering. I would only use the osage for belly wood and a lighter wood for a center lam. These would be for boo backing or hickory backing. Quarter sawn or bias sawn are preferred but flat grain will work also.
I, personally, would made a self bow out of a knotty stave. They look cool when done and it will teach you more about bow building than you could imagine.
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If you take your time with it and only work on it when you really want to you can make yourself proud with a beautiful character bow.
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Pat