US Patent 7338351 Apparatus and method for sharpening tool blades

A sharpening device for the blade of a tool such as a chisel or plane is in two parts. The first is a jig into which the blade is inserted with its tapered end projecting some distance beyond the jig. This distance is related to the angle to which the blade is to be sharpened. The second part is a marked reference member which is brought into a position alongside the jig. The blade is advanced through the jig until its tip reaches a marking on the reference member corresponding to the required sharpening angle for the tool. The tool is then clamped in the jig. The jig incorporates a roller which rolls on the sharpening stone while the tapered tip of the blade is sharpened by contact with the stone.