Lathe & mill
Surface finish predictor
What finish a feed leaves, or what feed a print's Ra callout allows. For a ball end mill, the cusp a stepover leaves, or the stepover for a cusp.
Finish
—µin Ra
The geometric ideal. Chatter, built-up edge, wear and a soft setup make real finish worse.
The last digit of the insert code: 2 = 1/32″, 08 = 0.8 mm
Show the math
Fill in the fields to see it worked out.
Rz (peak to valley) = f² ÷ 8r; Ra is about a quarter of it (Sandvik, Mitsubishi).
Related tools
- Turning troubleshooterStringy chips, chatter, a torn finish, built-up edge or chipped inserts: causes and what to change.
- Turning speeds & feedsMaterial, insert and setup to speed, feed, DOC, RPM and G-code.
- Milling speeds & feedsEnd mill, material and cut to RPM, chip load and IPM, with chip thinning.