Guides / For Machine Shops

The Overage Conversation Every Shop Should Start

September 25, 2026

A machined aluminium case that has been blasted and anodised cannot be reworked. A scratch found at final inspection is not a polish and a touch up, it is a new part from raw stock, back through every operation.

That single fact is the whole of this article. Everything else follows from it.

Why this work scraps and your normal work does not

On a functional part, a light mark on a face nobody sees is cosmetically irrelevant and dimensionally irrelevant. It ships.

On a keyboard case, the surface is the product. The buyer will hold it under a desk lamp within an hour of opening the box, and they will photograph it and post the photograph. A mark that would never have been noticed on a bracket is a rejected part here.

And because the oxide layer is transparent and grown out of the metal, anodising hides nothing. Every witness mark, every blast inconsistency and every handling scratch underneath it shows through, magnified rather than covered.

So a run of two hundred good cases requires more than two hundred blanks. The only question is who pays for the difference.

Three ways shops handle it, and two of them are wrong

Absorb it silently. You quote two hundred, you start two hundred and twelve, and you eat the twelve. This works until a run goes badly, and then a job you priced at a reasonable margin delivers at a loss. Worse, you have taught the customer that overage is free, which makes the next negotiation harder.

Promise exact quantities. You quote two hundred good parts from two hundred blanks. Every experienced buyer in this niche reads that as inexperience, because it is. And when the run comes up short, you are choosing between shipping a marginal part and telling the customer late.

State it and price it. You quote a number, explain why, and agree who carries it. This is the only version that survives a bad batch.

How to state it

Two sentences in the quote:

Priced with a cosmetic overage of X percent. Blanks started: 200 plus overage. Good parts above the ordered quantity are available at the per unit machining rate, or scrapped at your instruction.

That is it. It converts an invisible risk into a visible line, and a visible line can be negotiated instead of argued about.

Where your number comes from

Not from an article. From your own history on comparable cosmetic work, adjusted for three things:

The finish. A fine bead blast with a bright anodised colour is the least forgiving combination in common use. A coarser texture or an e-coat hides more and scraps less.

The geometry. Long flat visible faces scrap more than broken up surfaces. Sharp external edges take damage in handling. A deep pocket that requires a long reach tool is a chatter risk on a face somebody will look at.

The customer’s standard. This is the biggest variable and the one you can influence. A written standard with zones and viewing conditions can halve your realistic scrap rate compared to an unwritten expectation of perfection, because you are no longer rejecting parts against an imaginary bar.

If you have no history on cosmetic aluminium at all, say so and quote the first run with a larger overage and an offer to revise it on the repeat. Customers respect that far more than a confident number you cannot support.

Get the standard written, then quote against it

The scrap rate and the cosmetic standard are the same conversation. You cannot price one without the other.

If the enquiry arrives without a standard, ask for one before you quote. Viewing distance, lighting, duration, zones and per zone limits for scratches, blast variation and racking marks. If the customer does not have one, point them at a template.

This is not pedantry, it is self defence. Without it, the inspection bar moves after the parts exist, and it always moves in one direction.

Racking marks are not scrap

Worth its own paragraph, because it causes arguments.

Anodising requires the part to be held, and the contact point does not take colour. That is physics, not a defect, and every anodised part on earth has one somewhere.

Agree where it is allowed to sit before production. Underside, inside a screw recess, on a face that mates with another part. Get it on the drawing. A customer who discovers a racking mark on the front face in month five is entitled to be upset, and a customer who agreed its location in month one is not.

The spares are worth money to both of you

At the end of a run you will usually have good parts above the ordered quantity. Do not scrap them by default.

Group buy organisers want spares. Units get damaged in transit, parcels go missing, and a buyer whose case arrives dented is a refund unless there is a replacement on the shelf. Many organisers will happily buy the extras at the machining rate.

Agree the destination of spares in the quote, alongside the overage. It turns the last awkward conversation of the project into a line item that was settled in month one.

What good looks like

A quote that says: here is the per unit price, here is the overage and why, here is who carries it, here is what happens to spares, and here is the cosmetic standard I am quoting against.

Five lines. They will not lose you the job. They will filter out the customers who were going to be a problem, and they will win you the ones who have been burned before and can recognise a shop that has done this.

Frequently asked questions

Keep reading

• Should Your Shop Run Anodising In House?
• Why Your Anodiser Decides Whether You Keep This Work