DIGITAL MACHINEDESIGN DESK / DFM-05

Surface finish & coatings

Treat texture, appearance and coating requirements as separate decisions.

DESIGN INTENTDeposits shrink bores and grow outside diameters.
01Before: machined bore
Section through a bore with gray substrate on both sides. An arrow across the open space measures the initial 10.000 mm diameter.

Initial diameter = 10.000 mm

02After: inward deposit on both walls
The same bore after an ideal uniform deposit. Gold layers project into the opening from both walls. The finished opening is 9.980 mm, reduced by 0.020 mm total.

Finished diameter = 9.980 mm

WORKED EXAMPLE / mm

Bore: Dfinal = Dinitial - 2t | Outside diameter: + 2t

10.000 - (2 x 0.010) = 9.980 mm
03Separate texture from looks

A process name or cosmetic sample is not a roughness value. State parameter and units where texture affects function.

CAD: mark functional and cosmetic zones.

04Show what stays uncoated

Masking keeps selected surfaces free of a coating. Identify critical bores, threads, contacts and datum features; define mask boundaries.

CAD: mark no-coat and contact-restriction zones.

05Review edges and recesses

Local buildup depends on geometry and process access. The uniform 2t example does not predict coating distribution.

CAD: agree actual allowance before sizing fits.

06Define the complete finish

State process specification/revision, required records and final size. Digital Machine coordinates outside special processes; color is not equivalence.

CAD: call out the finish and acceptance condition.

WHAT THIS DOES NOT PROVE

Here t is buildup beyond the original surface, not automatically total coating thickness. Anodizing also penetrates the substrate; use process-specific growth data.

BEFORE RELEASE Protect fit, loads, sealing and required material sections when changing geometry.
  • Separate cosmetic zones from functional surfaces.
  • State roughness parameter and units.
  • Specify coating type and governing revision.
  • Identify masking and rack/contact restrictions.
  • State pre- or post-finish dimensional acceptance.
  • Request required process certificates and inspection records.