The Angle Follows the Job: Razor, Chisel, Knife, Axe

What does it cut? Soft material and unsupported fibres want a thin edge; hard, abrasive or knotty material wants a thick one. How is it driven? Hand pressure permits a thin edge. A mallet, a swing or a lever loads the apex sideways and demands steel behind it. This is the question people skip, and it is the one that breaks edges. How good is the steel? Harder and finer-grained steel holds a thinner edge. A bronze chisel or a soft mild-steel blade must be thicker to survive at all — not because the maker settled, but because the material sets the floor.

Set the blade bevel-down on a flat surface with a known stack under the spine and the angle follows from the geometry: sin(angle) = stack height / blade projection. A honing guide converts that directly into a projection setting. Do this before changing anything. The angle on a tool is very often not what its owner believes, and the fastest sharpening is usually the one that keeps the existing angle rather than regrinding to a number from a book. Write the measured projection on the tool handle in marker. Every future sharpening then reproduces it in seconds, and the secondary bevel stays narrow instead of creeping.

Read the failure and it names the fix. Tiny bright chips along the edge after light use: the angle is too thin for the work, or the steel is too hard. Go two or three degrees blunter on the secondary bevel and try again. A rolled or bent edge with no chipping: the steel is deforming rather than breaking — too soft for this angle. Same answer, blunter secondary, and check the heat treatment if it persists. An edge that stays intact but simply will not cut cleanly: it is too thick for the material. Go thinner, a couple of degrees at a time. Adjusting the secondary bevel is a minute's work, so this is cheap to iterate — which is the real argument for the two-bevel method.