Guides / Finishing

Agreeing What Counts as a Defect Before You Order

September 21, 2026

Machining tolerances are numbers, so they are easy to agree. Cosmetic quality is a judgement, so it is where most disputes in this niche end up.

The fix is not to demand perfection. It is to write down, before anyone cuts metal, what acceptable looks like and how it gets checked.

Why “flawless” fails

A shop cannot price flawless because it cannot inspect flawless. There is no measurement, no threshold and no way to know when a part passes.

What actually happens when you write it is one of two things. A careful shop adds a large allowance for scrap and rework and your quote comes back high. A less careful shop agrees, ships, and you have the argument later with nothing written down to settle it.

Both outcomes cost more than the fifteen minutes it takes to define a real standard.

Define viewing conditions

Every cosmetic standard needs three things: how far away, how long and under what light.

A workable default for a keyboard case:

Inspected at 400 mm under diffuse office lighting of roughly 500 lux, for 10 seconds per surface.

That is roughly how someone looks at a board on their desk. It excludes defects only visible at 100 mm under a raking spotlight, which is fair, because that is not how the product is used.

Write the numbers. “Normal lighting” and “arm’s length” mean different things in different workshops.

Define zones

Not every surface on a case deserves the same standard. Zoning is the single most effective thing you can do to control cost.

A typical three zone scheme:

Zone A, primary. The top surface, the front face and the sides. Everything a buyer sees constantly. Highest standard.

Zone B, secondary. The underside, the back face and the area around the port cutout. Visible occasionally. A relaxed standard.

Zone C, hidden. Internal pockets, gasket shelves, anything under the plate. Functional only, no cosmetic requirement at all beyond being clean and burr free.

Mark the zones on the drawing. A shop that knows zone C is hidden will not slow down a finishing pass for it, and that is real money.

Define defect types and limits

You do not need a page per defect. You need the four that actually occur:

Scratches and witness marks. State a maximum length and whether any are allowed in zone A at all.

Blast inconsistency. Patches of visibly different texture. Usually zero in zone A.

Racking marks. Anodising requires the part to be held, and the contact point does not take colour properly. Decide where racking marks are allowed to sit and put it on the drawing. This is a normal and unavoidable feature of the process, and designers who do not specify it get to be surprised by wherever the anodiser chose.

Colour variation. Handled by the golden sample rather than by a description. See colour matching across a run.

The golden sample settles everything else

Words go so far. A physical approved part goes the rest of the way.

Once you approve a prototype, name it in writing as the acceptance standard, keep a copy each where possible and inspect production against it. When someone says a batch is too light or the blast is too coarse, the sample answers rather than the email thread.

This is one of the main reasons a prototype is worth its cost even when you are confident about the design.

Agree the overage before you order

Cosmetic machining scraps parts. On an anodised finish there is no rework, so a rejected part is replaced from raw stock.

That means a shop making 180 good cases starts more than 180. Three things need agreeing up front:

1. What the expected overage is, as a number.
2. Who pays for it.
3. What happens to any good spares at the end.

Many organisers sell the spares, which converts a cost into a buffer against transit damage and lost parcels. That is a much better conversation to have in month one than in month seven.

Put it on one page

A complete cosmetic standard for a keyboard case fits on a single sheet:

• Viewing distance, duration and lighting
• Zone map with the standard for each zone
• Limits for scratches, blast variation and racking marks
• Allowed racking locations
• Colour governed by the approved golden sample
• Expected overage and who pays
• What happens when a batch is borderline

Attach it to the RFQ. Shops quoting against a clear standard quote lower and argue less, and you will get comparable numbers back instead of three prices that were each guessing at a different definition of good.

Frequently asked questions

Keep reading

• Two Colours on One Case: What Masking Adds to an Anodised Run
• Specifying E-White So Cases Match Each Other and the Keycaps