Sources and scope for this page: Industry convention — no single governing standard (conventional usage, definitions vary between sources), covering the definition of gummy (material). No independent source check is recorded for this page: the content rests on the sources listed and on the working shown on the page. How sources, methods and updates are recorded.
Definition
"Gummy" is not a formal property, but it describes a real behaviour: low-carbon steel, pure aluminium, copper, austenitic stainless and many plastics all tend to deform plastically ahead of the edge rather than shearing cleanly. The result is a smeared finish, poor chip control and built-up edge.
The remedies overlap: sharper and more positive rake, higher surface speed, and a polished tool face to reduce adhesion. Free-machining additives address it at the material level.
Common misuse
Attacking a gummy material with a heavier feed to "force" a chip. It usually makes the smear worse — speed and edge geometry are the levers.