some woods are more challenging than others,,to recuce frustration and increase success,, maybe just straight hickory,,, or something that is more forgiving, I have made nice bows from hickory boards,, I did have failures with backed bows, the tiller has to be more exact,, i think your failures are more the challenging wood than what you are doing,, try to keep it simple at first,,,, like you said its heartbreaking to pu that much work in and have it fail,, thats why investing in a good osage stave might be worth it,,time spent ,, usually comes with a shooter ,, that will outlast most bows,,