Guides / Sourcing / Design for Manufacture

Telling a Machine Shop Which Faces the Customer Will See

July 22, 2026

Every machine shop understands a tolerance. Very few have a process for appearance, because appearance is not usually on the drawing. On an audio part it is the most important thing on the drawing and it is almost always missing.

Why “cosmetic” needs defining

A machinist looking at a front panel sees a plate with holes in it. Nothing in the geometry says that the front face will be under a customer’s desk lamp for ten years and the rear face will never be seen again.

Without that information the shop has two choices, and both cost you:

Treat everything as cosmetic. Slower handling, more inspection, higher price, more rejects.
Treat nothing as cosmetic. Correct part, scuffed face, rejected batch, argument.

A three zone scheme

Define this once in your drawing template and use it on every part.

Zone A. Primary cosmetic. Seen by the customer in normal use, at close range, in good light. The front face of a panel, the top of a knob, the visible flank of a cup.

No scratches, dents, tool marks, rack marks or handling marks visible at 300 mm under diffuse light
Uniform texture and colour across the whole zone
Colour to match the approved reference sample

Zone B. Secondary cosmetic. Visible but not the focus. The sides of a chassis, the underside of a chamfer, an area behind a control.

No defects visible at 600 mm
Minor texture variation acceptable
Rack marks permitted only if noted on the drawing

Zone C. Non-cosmetic. Never seen once assembled. Internal faces, mounting bosses, the back of a panel.

Function only
Burr free where it matters for assembly and safety
Rack points and fixture marks permitted here

Then on the drawing, label the faces. A hatched region with a leader and “ZONE A” is unambiguous. A note saying “front is cosmetic” is not, because it does not say where the front stops.

The acceptance criteria that make it real

Three numbers turn an opinion into a test:

Viewing distance. 300 mm for Zone A, 600 mm for Zone B.
Light. “D65 diffuse illumination” is the usual reference. The key word is diffuse. A point light source shows defects that nobody will ever see in a living room, and a dim room hides ones they will.
Time. Some schemes allow five or ten seconds per face. It sounds arbitrary and it stops an inspector hunting for a defect with a loupe for two minutes.

Add the angle if the finish is directional. A brushed surface inspected along the grain and across the grain looks like two different parts.

What else belongs in the cosmetic block

Rack point location. Every anodized part has a contact mark. If you do not choose where, the finisher will, and it may be in the middle of Zone A. Specify a blind tapped hole or an edge in Zone C.
Grain direction, with an arrow on the view.
Edge treatment. “Break all edges 0.3 max” is a machining note. “All Zone A edges to be uniform and free of witness lines” is a cosmetic one. You may need both.
Handling requirements. Gloves after finishing, no stacking face to face, protective film on Zone A before shipping.
Reference sample. Which one, whose copy, dated.

A drawing note you can copy

COSMETIC SPECIFICATION

ZONE A (HATCHED): FRONT FACE AND TOP CHAMFER.
  NO SCRATCHES, DENTS, TOOL MARKS OR HANDLING MARKS
  VISIBLE AT 300 mm UNDER D65 DIFFUSE LIGHT, 10 SECONDS PER FACE.
  TEXTURE AND COLOUR UNIFORM. COLOUR TO MATCH SAMPLE REF 1042-A
  DATED 2026-03-14, HELD BY SUPPLIER AND BY CUSTOMER.

ZONE B: LEFT AND RIGHT END FACES.
  NO DEFECTS VISIBLE AT 600 mm. MINOR TEXTURE VARIATION ACCEPTED.

ZONE C: ALL OTHER SURFACES. FUNCTIONAL ONLY.
  RACK POINTS AND FIXTURE MARKS PERMITTED IN ZONE C ONLY.
  RACK ON M4 BLIND HOLE, REAR FACE, SEE VIEW B.

HANDLING: GLOVES FROM BRUSHING OPERATION ONWARDS.
  NO STACKING FACE TO FACE. PROTECTIVE FILM ON ZONE A
  BEFORE PACKING, APPLIED AFTER ANODIZE ONLY.

Tolerancing only what matters

The same discipline applies to dimensions. On a typical front panel:

Panel gaps and visible fits: tight, because the eye reads them. Plus or minus 0.05 mm is reasonable on a cutout that a knob passes through.
Connector cutouts: the connector has its own tolerance and usually a bezel that hides the edge. Plus or minus 0.2 mm is often plenty.
Mounting holes on hidden faces: general tolerance.
Overall thickness where nothing mates: general tolerance.

A general tolerance block of plus or minus 0.1 mm across an entire panel, with three critical features called out tighter, prices far better than plus or minus 0.02 mm everywhere.

The payoff

A drawing with a cosmetic block gets:

Quotes that are comparable, because every shop is pricing the same job
Fewer questions during the quote
A defined basis for accepting or rejecting the first article
A standard that survives when the person who designed the part leaves

Frequently asked questions

Is there a standard for cosmetic specifications?

Nothing as universal as GD&T. Some industries use scratch and dig notation borrowed from optics, others use their own zone systems. In practice a three zone scheme defined on your own drawing, plus a reference sample, is clearer than citing a standard the shop has never used.

Can I just write no visible defects?

You can, and the shop will either price for perfection or ignore it. Neither helps. Visible at what distance, under what light, by whom? Without those three, the phrase means nothing and it will be argued about after the parts are made.

Does marking cosmetic faces make the part more expensive?

Marking them makes the part cheaper. Not marking them means the shop either treats every face as critical, which costs more, or treats none as critical, which costs you a rejected batch. Specificity is the discount.

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Keep reading

This guide is part of Sourcing and Quality Control for Audio Parts, one of four sections in the guide library.