Chisel angles: what 25 and 30 degrees do
Most bench chisels do well with a primary bevel of 25 degrees and a micro bevel of 30. The primary bevel sets the shape of the edge, and the micro bevel is the small face you actually resharpen.
Why two bevels
Grinding or honing the full bevel takes a long time. Adding a micro bevel a few degrees steeper at the very tip means you only polish a sliver of steel each time. After several touch-ups the sliver grows, and you go back to the coarse stone to restore the primary bevel.
Which angle for which job
- Paring chisels, used by hand in softwood: 20 to 25 degrees. Sharp and delicate.
- General bench chisels: 25 degrees with a 30 degree micro bevel.
- Mortise chisels and anything struck with a mallet in hardwood: closer to 30 degrees, for a tougher edge.
The flat back
The back of the chisel matters as much as the bevel. Flatten the first few centimetres on a coarse stone until the scratch pattern runs right to the edge, then polish it. A bevel can only be as sharp as the back it meets.
Keep a simple routine: back, bevel, a few strokes on the finest stone, then test on end grain. If it shaves a clean curl, put it down and cut something.