The general aim to try an follow a ring, but there may be areas where you need to violate rings. Try to make the violations rul along the length of the bow or at an oblique angle.
It's more important to try to keep a reasonable layer of sapwood say 4 - 5mm all over. Bear in mind the heart/sap boundary doesn't always follow a ring and can shift over the width of a bow. I had one ELB I named ridgeback as it had a streak of heartwood showing up the back at one point, it turned into a fine bow.
http://bowyersdiary.blogspot.co.uk/2012/04/weird-heartsap-boundary-emails.htmlIt's sudden changes or breaks in the sapwood going across the bow that spell trouble , or big knots that don't stand a bit proud.
The attached pic shows the back of my big old Yew ELB, you can see the heartwood dips down. If I followed a sap wood ring I'd have ended up with no heart wood. the solution was to reduce the thickness of the sapwood. You can see I've gone down through about 8 rings, pretty much right across the bow... conventional wisdow would say the sky would fall in... it didn't. But you can see I've kept a good layer of sapwood.
I'd say ideally you want about twice as much heart as sap, but one to one is ok. What you don't want is a gap in the sapwood or a really thin patch.
OK that's an extreme example, but those two examples give a fair idea of what you can live with.
I'm sure you wouldn't get away with violations like that on Osage!
Hope that sets your mind at reat.
Del
