I have tried the sap wood method with agonizing results. The backs would either break, or the bellies fretted. Probably me , not the wood. I made 4 with no luck with that wood. Then I found a thicker ringed log ,and chased a clean ring into the heart wood. All of those came out good with no breaks, or frets, so I favor chasing a heart wood ring with Black Locust . Same thing with Osage. JMO. Good luck with yours.