Sharpening angles
Plane cutters and chisel blades, like Ma¯ori adze blades, have cutting edges formed where a bevelled front meets a flat back. The smaller the angle between the two surfaces, the sharper the edge, but the more likely it is to chip and the longer it takes to sharpen. A compromise is needed, which usually results in an angle of about 30 degrees between the ground faces. In his book on scything, “The Scythe Book”, “The Scythe Must Dance “(2001), Peter Vido called it “the compromise between penetration and durability”.
The sharpening angle is important in plane cutters that are held at a fixed angle to the surface being worked, and instructions as to the correct angles can sometimes be found engraved on the chip-breaker of the plane. The plane works best when the cutter is sharpened to the indicated angle. Thin plane cutters are more easily sharpened than older, thicker ones because less metal has to be removed.
Many devices have been invented to aid the sharpening of cutters to a particular angle and examples, both cheap and expensive, are still available today. These sharpening jigs work by holding the cutter at a fixed angle to the surface of the sharpening material. Some hold the cutter at an angle to the direction of movement also, so that the cutting edge is also at an angle to the length of the cutter, which may provide a better cutting action in use.