Lathe

turn the spinning blank down to the pencil line.

a woodturning lathe: press the chisel into a spinning maple blank to match the outline

The chisel takes wood wherever its edge sits, a little every moment, so holding it longer takes more, and nothing grows back. Each piece is scored by how much of the wood the outline asked for you took, and no more.

Concepts: subtraction, patience.

An interactive you play with one thumb, on Wundr.