Different processes.
Different finishes.
Process-driven appearance.
Each manufacturing process leaves characteristic surface finish. Milled lines, turned circumferential marks, ground lines, cast textures. Match expected finish to process.
Key principles.
Tool path lines
Visible tool paths in machining direction. Ra 1.6-3.2 µm typical.
Circumferential rings
Concentric ring marks from rotational cutting. Ra 0.4-1.6 µm achievable.
Linear lines
Linear grinding marks. Ra 0.2-0.8 µm.
Matte finish
Random matte texture. Ra 1.6-6.3 µm depending on settings.
Striated edge
Slight striation marks on cut edge. Ra 3.2-6.3 µm.
Granular texture
Sand-cast: rough granular. Investment cast: smoother. Die cast: smoothest.
As-rolled
Original mill finish unless processed. Slight tooling marks at bend lines.
Uniform matte
Even matte finish. Ra 1.6-6.3 µm depending on bead size.
Layer lines
Visible layer lines per print process. Smoother with finer layers.
FAQ
How do I specify finish on drawing?
Use ISO 1302 or ASME Y14.36 surface finish symbols. Specify Ra value, direction (lay), or finish process (e.g., "ground", "polished").
Achievable Ra by process?
Mill 1.6 µm. Turn 0.4 µm. Grind 0.2 µm. Polish 0.05 µm. EDM 1.6 µm. Laser cut 3.2 µm. Each process has practical limit.
Combining processes for finish?
Common: mill rough + grind precision + polish cosmetic. Each step adds time + cost. Specify minimum needed.
Heat treatment affects finish?
Heat treat distorts surface, requires re-finishing. Specify finish after heat treat for tight Ra.
Cleaning vs finishing?
Cleaning removes contamination. Finishing changes surface. Both may be needed — clean before paint, polish for cosmetic.
Documentation?
Surface finish per drawing spec verified by surface profilometer. Record kept per part lot.
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