id say 95% of the staves i correct are corrected,shaped,and tempered all in one session. it should only take once in most circumstances(and yes even with nasty staves) to make all the corrections and shaping. a form,some shims,and a heat gun will work wonders(especially with osage). personally i dont like the thought or idea of having to heat up a stave too many times,especially in the same areas that were already heated previously. thats just my two cents and opinion