Recommended Method of Sharpening Round Edge Edgers:
With each round edge edger, Ron's supplies a metal rod sized to the concave of the tool purchased (any round rod of the appropriate size will work).
To properly sharpen the tool, lay the rod on your workbench and place a piece of 400-600 grit emery paper over the rod. Rub the cutting tool over the emery paper as you would a sharpening stone, feeding new paper to the work area as needed. Move the rear of the handle up and down as you rub it over the rod to prevent making a flat spot on the cutting edge. We suggest you feed the emery paper over the rod from alternating sides to prevent the cutting edge from being ground off-center by having the fresh grit on the same side as the tool.
After sharpening the tool, fold the emery paper or lay it over a piece of leather the appropriate width and use this as a device to strop the inside edge of the cutting tool. Finish smoothing the edges by buffing both the inside and outside of the tool. This method of sharpening maintains the correct radius on the cutting edge of your tool.
See how to sharpen the Round Edge and Montana Edgers. (Embed one of these videos)