The basics of rotary engraving: a rotating tool with a cutting lip is dug into a piece of material to remove material in its path. (A cutter or bit is the common term; the old term is needle). The cutters come in various configurations and tip sizes to allow more or less material to be removed. With manual engravers much of the machine’s speeds and feeds are controlled by the operator.
The depth of engraving is controlled by a couple of ways. A cutter is stopped by a defined amount by a stepper motor or a mechanical stop. Most utilized is a nose (a non-cutting ring around cutter) that allows depth to be regulated.
-Fred Schwartz, Quality One Engravers