Worked on my mower.  It took long to sharpen the incredibly old blades.  I had to very slightly tighten the main cutting bar and wipe/apply the lapping compound about four times before getting good results.  It takes very little compound to sharpen. After the last application and tightening I turned the blades back with the included handle a few hundred times and as it started turning easily it got a very smooth action.  It mows like a dream now.