Sources and scope for this page: ISO 3002-1:1982, covering the definition of clearance angle. 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
The clearance angle exists purely to stop the tool rubbing on the surface it has just cut. Without it, the flank contacts the work, generates heat by friction instead of by cutting, and the edge fails quickly.
Typical values run 6° to 8° for general turning, larger for soft gummy materials that spring back toward the tool, and smaller for heavy roughing where edge strength matters more. On an indexable insert the clearance angle is encoded in the second letter of the ISO designation — C is 7°, P is 11°, N is 0°.
Common misuse
Assuming a larger clearance angle is always better. Too much clearance weakens the edge and causes chipping, especially on interrupted cuts.