Surface Finish Guide: Ra Values and What Achieves Them
What Ra numbers mean on drawings, which finishes milling and turning reach in practice, and the machine and tooling factors behind each step.
Ra appears on every drawing, yet many buyers quote it without knowing what it costs. Ra 3.2 microns is ordinary milling territory. Ra 1.6 asks for sharper tooling and steadier feeds. Ra 0.8 and below usually means a dedicated finish pass, better spindle condition and sometimes grinding.
What Different Finishes Need
- Ra 6.3 to 3.2: standard roughing and semi-finishing cutters, any healthy VMC.
- Ra 1.6: fresh geometries, light radial passes, low runout holders.
- Ra 0.8: high-speed finishing passes, thermal-stable machine, clean coolant.
- Ra 0.4 and below: grinding or honing territory for most steels.
Finish correlates strongly with machine health. Worn ballscrews create banding; a spindle with runout leaves scallops no parameter table can hide. That is why our run-off test measures surface finish on real cut pieces, not just geometric checks.
Tell us the Ra your drawings demand and we will confirm which machine class holds it in production, not just on day one.
Talk to VITOP Machinery
Questions about this topic or your upcoming project? Email vitopmachinery@163.com or message us on WhatsApp: +86 183 1908 0212. Browse all machines at www.vitopmachinery.com. We reply within one business day.