A reel mower cuts grass by trapping it between a rotating blade and fixed blade. The basic idea behind sharpening a reel mower is this: using lapping compound, a kind of oily grit, you accelerate the wear between the blades and the cutting bar in such a way as to produce a tiny, but consistent gap between the working parts. Too much gap, and the grass is squeezed through the blades without being cut; too little gap, and the grass is cut, but the mower is difficult to push or use.

The sharpening process takes a couple of steps:

1. Assemble tools and materials
2. Measure the health of your mower to find out how much sharpening you need to do.
3. Disassemble and reassemble your mower enough to make it so that the wheels drive the blades in the backwards direction. I’ll explain why this is important shortly.
4. Apply lapping compound to the blades, and ajust the cutting bar.
5. Push the mower to drive the blades backwards.
6. Clean the lapping compound off the blades.
7. Restore the wheel drive to forward-only operation.

How is this different from what a commercial sharpening service does? It depends on the sharpening service - many do some variant of this procedure, though with a belt driving the blade assembly - there is less to disassemble that way. Other shops have fancy grinding jigs that can actually do a better job than you can do at home. A grinding jig is capable of bringing the blade edge to a wedge shape that minimizes contact with the cutting bed blade. However, you will pay significantly for this type of service.

There are kits available on the Internet that provide a handle to turn the blade, along with grit. However, I think it is easier to just push the mower.

Safety warning

Reel mowers, with their exposed blades, can be dangerous. Never put your hand or fingers into the blades while they are rotating, and be careful when applying force to a blade assembly that is tight and resisting rotation- it may suddenly break free with your fingers in a place where they could get cut or crushed. Easy does it. Finally, remember that your mower will be sharper after this process, and you might get cut on a blade that used to be dull.