A couple of simple points Aussie Blue. First, I take it you run your DeWalt with the impact feature switched off. When I read morphias' post I momentarily visualised following this procedure with my rotary hammer drill, pushing it forward to deliver the standard 3,000 hammer blows of 3.8 Joules each, per minute, and figured the ballraces would last less than a second and the mower frame probably less than a minute. That would be a great way to get plenty of drill-power onto the job, but not a great outcome. Second, the general concern I have with back-lapping is that over time, the bedknife and the reel will both become wavy (the waves in the two parts will match each other, of course), so when you eventually get them ground, you will probably have to remove considerably more metal. So, the secret seems to be to keep a close watch on the flatness of the bedknife (since it will become exactly as wavy as the reel). When the first trace of waviness appears, it is time for a spin-grind and bedknife grind.
Note: 3.8 Joules impact energy is equivalent to dropping a two pound hammer on it from a height of seventeen inches.
