I own a very large metal file, and I use it to sharpen my lawnmower blade. Everything I’ve ever read about sharpening a mower blade indicated you don’t ever use power equipment. By that I mean something that spins at a high rate of speed with a sharpening wheel attached. The reason given is always the same. The steel used in lawnmower blades is hardened along the edges to hold the sharpness longer. When you try to resharpen the blade using a high speed spinning sharpening stone, the metal in the blade heats up. Sometimes it can heat up so much the metal turns color. When you see that color, you have effectively removed the hardening of the steel. It will now be just as soft as a wire coat hanger and not hold the sharp edge for very long. However today I read in Consumer Reports blog that they use a Dremel tool with a blade sharpening attachment. How is this different from your average cheap bench grinder? It’s hand held, but other than that, does it heat up the blade any less? I also have one of the electric drill attachments they mention in the article. I don’t use that tool for the same reason why I probably wouldn’t use the Dremel attachment, it’s going to heat up the blade as the sharpening progresses.
Another good sharpening option is Dremels Lawn Mower & Garden Tool Sharpener attachment about $8 is. Peter Sawchuk, our outdoor-power-equipment expert, uses this attachment at our mower/tractor-testing site in Fort Myers, Florida, where we check out several dozen models every year. “I see value in the attachment for homeowners,” says Sawchuk, noting that the nylon guide holds the blade at the right angle for maximum sharpness. In Sawchuks experience, the only drawback to the attachment is that it cant grind out major nicks. You can also get similar drill attachments for sharpening a mower blade. Properly clamping the blade in a stationary position and using two hands to guide the tool will help you get a uniformly sharp cutting edge.
from consumer reports