Dan had done a great post on the arched grind line, I call it the SWOOSH. Anyway I could never get it to work and after many frustrating attempts decided there had to be a better way at least for me there had to be a better way. I rough grind all my blades on a 2x72 and then it is off to the lap wheel to final grind and finish them. I consider my lap wheels the most important piece of equipment in my shop. Note : my lap wheels (disk grinders ) run at 1200 RPM are reversible and have 1 degree bevel on the face so the blade does not touch the wheel on the other side of centre. Anyway here is the process that I use and has worked for me.