NO! NO! NO!. Spin grinding is the process which txgrassguy described where a reel is spun by one drive and a grinding stone is spun by another, grinding the reel into a true cylinder. What I see happening even in my state where reel mowers are very common, is that is the extent of the sharpening. The next steps of relief grinding and backlapping to achieve a very slight gap along the entire length of the reel is totally skipped. If I see that the face of the reel is perfectly flat and the mower has to be adjusted to a really wide gap, my temptation is to drop that mower on the head of the person that did that. All he did was grind metal off the blades and ensure that the person would be back in short order because the machine stopped cutting cleanly. Backlapping is when a water based gel with silicon carbide is applied to a reel with a relief grind and then it is spun backwards. That and face grinding a bedknife are two relatively simple procedures that can restore quality of cut to a mower that is not rounded, nicked or otherwise severely damaged.