Rule 19 of 31 · Chapter IV — Keep Tools Sharp
Match the bevel to the job
Why this rule exists
The angle you grind an edge to is a trade between sharpness and durability. A low bevel slices sweetly but crumbles in hard wood; a steep bevel survives abuse but needs more push. Grind a paring chisel like a mortise chisel and it tires you out; grind a mortise chisel like a paring chisel and it chips on the very first blow. Picking the right angle for the work makes the tool feel built for exactly that task.
In practice
Aim around twenty-five degrees for general bench chisels and plane irons, dropping toward twenty for paring softwood, and climbing to thirty or more for mortising and chopping hardwood. Add a small secondary micro-bevel so honing is quick and you're not regrinding the whole face each time. Use a honing guide until the angles are muscle memory in your hands. If an edge keeps chipping, steepen it a touch; if it feels dull too fast, it may just need honing, not regrinding.
When it doesn't apply
Freehand sharpeners often run one consistent bevel across tools and adjust their technique instead, and that works fine once skilled. Specialized edges, like a steep scraper burr or a skewed paring angle, follow their own rules. Treat these angles as sensible starting points, then tune to your wood and your feel.