Hi Jeff, welcome to Outdoorking. The purpose of the Bedknife Buddy is to sharpen the cutting edge of the bedknife, the fixed blade of a reel-type mower. Grass is cut scissors-fashion by the reel blades sweeping the grass back against the bedknife. The top of the bedknife needs to be ground flat and kept flat, and its front edge needs to be flattened in some suitable way and kept both flat, and at right angles to the top surface. You can't flatten the top of the bedknife without removing it from the mower and putting it on a surface grinder, so you protect it by very careful adjustment of the geometry so the reel's blades never actually touch the bedknife, though they miss it by less than 0.001". However the square edge at the front of the bedknife actually contacts grass, and wears away in the process. Occasionally you have to file or grind back the vertical front surface of the bedknife until its top corner is sharp again, instead of rounded by wear. Traditionally this was done by careful use of an oilstone. The Bedknife Buddy is a small tool that attempts to do it without requiring as much skill as an oilstone does.
Remember that the front surface of the bedknife must always be precisely flat along its whole length, and precisely parallel to the axle of the reel. This is very difficult to achieve and maintain, whether you use an oilstone or a Buddy. The advantage of the Buddy is that it keeps the front of the bedknife square to its top surface - keeping the front surface flat and parallel is still up to the person doing the sharpening.
