I don't know if this is something that Dave has shared publicly, so I'm a bit reluctant to share....don't want to step on toes.
Here is the before image of a pretty standard chamfering that we probably all learned:
Dave proved to me by multiple metrics that this approach will leave a very slightly raised ridge around the perimeter of the stone...kind of like a burr. this will affect your flattening as well as your sharpening....and it caused a flattening problem I've had with one stone for several months now.
by taking this approach:
Starting about 2" from the edge and going all the way out, create a continuously decreasing radius compound curve. This is guaranteed to eliminate the ridge and reduce the chances of gouging the edge of the stone with the edge of your knife. It has the adverse effect of reducing the (easily) useful area of the stone.
Hope this makes sense.
i think i know and have the same problem, but my english is not good enough to understand the problem solving. need to read through this a few more times :D
i think i got it now, thanks. gonna try it out tommorow.
The idea is to remove the sharp corners/edges of the stone by rounding vs chamfering. By doing a series of overlapping chamfers you create a radius. If you start with the lapping plate on the stone's face and work in a series of bevels/chamfers the edge/corner becomes rounded.
While you give up a small amount of edge contact area you gain the entire middle of the stone as a contact area and that's because the knife now makes contact across the face instead of just the high edges/corners of the stone. This little trick can really make some stone's come alive, sure makes coarse stones cut faster and for naturals it keeps the edges from scratching that perfect finish.
This also serves you when lapping a stone - on a new stone or one that needs a lot of lapping - first round the corners lap and round as needed during the process to keep the corners down/away from the lapping plate to allow the plate to work the stone's face - because these high corners/edges won't allow some stones to be flattened correctly or efficiently.
Just a note on Danny's pictures above, the rounded corner he shows is either a tad too round (meaning maybe it's been rounded more than necessary up onto the stone's face) or the picture is macro showing a huge gap where this isn't necessarily the case. The pictures are a good representation of the difference between chamfering and rounding though.
Japanese Sword sharpeners use stones high in the middle