The angle between the tool's flank and the machined surface, which prevents the flank from rubbing.
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°.
Assuming a larger clearance angle is always better. Too much clearance weakens the edge and causes chipping, especially on interrupted cuts.
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