Guides / For Machine Shops

Why Your Anodiser Decides Whether You Keep This Work

September 25, 2026

You can hold your dimensions. That was never the risk on this work.

Nearly every keyboard case run that goes badly goes badly at the finisher. The colour comes out light, the two halves do not match, a racking mark lands somewhere visible, or the batch arrives three weeks after the customer’s public ship date. None of those are machining problems and all of them are yours, because you are the one who quoted.

So the finishing relationship is not a purchasing detail here. It is the core capability you are selling.

Why colour moves at all

Anodising converts the aluminium surface into a porous oxide layer, draws dye into the pores and seals them. The colour lives inside the metal’s own oxide, which is why it wears so well and why so many things influence it.

Four variables move the result and you control two of them.

The alloy. Silicon and copper do not convert to clear oxide. They stay as particles and haze the colour. 6063 comes out brightest, 6061 slightly cooler and duller, 7075 darker and least predictable. You control this by refusing to let two alloys into one colourway.

The blast. Grit size sets the texture and the texture changes the apparent colour. A repeat run blasted at a different grit will not match the first. You control this by writing the grit as a number in your own work instruction, not as a word.

The dye bath. Dye depletes as parts are processed, temperature drifts across a shift, and time in the dye is judged by an operator. You do not control this. You contain it by batching.

The seal. Hot water sealing lightens the shade slightly, cold nickel holds it closer. Ask which your finisher uses and keep it consistent.

The one instruction that prevents most failures

Every part that has to match goes in the same load.

Top case, bottom case, any exterior accent. They meet in a seam that runs the whole perimeter of the board, and two loads of the same dye will not agree closely enough for that.

Put it on your purchase order to the finisher, in those words, not as a verbal request. Then put it on your order confirmation to the customer as well, so they can see you have done it. It costs nothing and it is the single highest value line in the whole job.

What to agree with your finisher before you quote

Five things, once, and then it applies to every keyboard job you take.

Batching. That they will hold your matching parts and run them together, even if it means waiting for a fuller load.

A sample process. That they will produce a single approved part first, at a sensible price, and keep a retained sample against which later batches are checked.

Racking discipline. Where contact points are allowed to sit on your parts. Get it agreed as a standing instruction, then put the allowed location on the drawing you send the customer.

Lead time, honestly. Their real queue, not their best case, and a commitment to tell you when it moves. You are going to quote this number to a customer with a public date.

What happens to a batch that misses. Strip and reprocess, accept with an adjustment, or remake. Agreeing the three options with your finisher before you need them means you can offer the customer the same three.

Quote finishing as its own line

Two reasons.

Buyers in this niche ask about the finish before they ask about the price, because they have read that it is where runs fail. A quote that shows finishing as a visible line with its own lead time reads as a shop that has thought about the real risk.

And the batch minimum is genuinely different from the per unit cost. On fifty cases the batch term can be a third of the finished price, and it barely changes at two hundred. Showing that separately explains your quantity curve for you, and it stops a customer thinking your machining is overpriced.

The golden sample protects you, not just them

When a customer approves a physical sample, that object becomes the acceptance standard for the run. Make sure it is written down as such, and keep a copy yourself.

This is usually framed as a buyer protection. It is at least as much a shop protection. Without it, “not quite the right blue” is an opinion formed in month five under a desk lamp, and you have nothing to point at. With it, both sides are holding the same object and the conversation takes ten minutes.

Repeat colourways: what to promise

A year later they want the same colour again. Treat it as a new colour and say so.

The dye lot is gone. The bath is different. Your finisher may have changed a process. What you can honestly offer is: we will get close, we will make a new sample and put it next to your original for approval, and we will tell you before production if there is a visible difference.

Customers accept that readily when it is said at the start. They do not accept it when it arrives as an explanation after two hundred cases have been made.

The short version

Pick one finisher and stay with them. Batch matching parts together, in writing. Get a sample approved and keep a copy. Quote their real lead time, separately. Never promise an exact repeat.

Do that and the cosmetic side of this work becomes as predictable as the machining, which is the whole difference between a shop that takes one keyboard job and a shop that keeps getting them.

If you want requests that already specify the alloy, the grit and the batching, see what we look for.

Frequently asked questions

Keep reading

• Should Your Shop Run Anodising In House?
• The Overage Conversation Every Shop Should Start