What a Custom CNC Auto Part Actually Costs

September 21, 2026

A quote for a machined automotive part rarely looks like the price of a catalog part, and the reason is that almost nothing in it is the metal. Most of what you pay for is time on a machine and the hours spent getting the machine ready.

Here is what sits inside a typical quote, in the order it usually matters.

Setup and programming

Before a cutter touches anything, someone opens your file, decides how the part will be held, writes the toolpaths, sets the tools and runs the first piece slowly to prove the program. On a prismatic bracket that might be two hours. On a part with features on five faces and a fixture that has to be made first, it can be a day.

That work is paid once per order. It does not get cheaper because you only want one piece. On a single prototype it is often the majority of the invoice, which is why a one off and a batch of five can come back at nearly the same total price.

The practical consequence: if you think you will want a second one, order both now.

Material

Two things drive the material line. The alloy, and the size of the block it gets cut from.

A shop buys a rectangular billet large enough to contain your part plus clamping stock. If your bracket is 200 mm long with one 30 mm boss sticking out, you are paying for a block tall enough for the boss across its whole length. Most of that metal ends up as chips.

Alloy matters twice. Titanium and 4340 cost more per kilo than 6061, and they also cut several times slower, so they add machine time as well as material cost. Moving a part from 6061 to 7075 is usually a small change on the invoice. Moving it to titanium is not.

Tolerance and finish

Every tolerance you tighten adds passes, slower feeds, better tooling and more inspection. A hole called out at plus or minus 0.01 mm gets bored and measured. The same hole at plus or minus 0.1 mm gets drilled and reamed and nobody thinks about it again.

The same is true of surface finish. Ra 1.6 comes off a normal finishing pass. Ra 0.8 on a large face means a slower pass with a fresh tool.

Tolerance what the part needs: the bores, the sealing faces, the positions that have to line up with something else. Leave the rest at a general tolerance and say so on the drawing.

Quantity

Setup spreads. That is the whole story of the quantity curve.

At one piece you carry all of the setup. At ten you carry a tenth of it each. By a hundred the setup barely shows and the price per part is close to the cycle time plus material, so the curve flattens out. Past that, further savings come from the shop changing the process rather than from spreading setup, which means better fixtures, more parts per load or a bar fed lathe instead of a mill.

If you are close to a quantity break, ask the shop where it is. Most will tell you plainly that 40 pieces costs almost the same as 25.

Finishing and secondary work

Anodizing, powder coat, zinc plating, heat treatment, thread inserts, laser marking. These usually go to a second vendor, so they add cost, freight and a few days of lead time. A shop that already has those vendors handles it in the quote. One that does not will either subcontract with a markup or ask you to arrange it.

Heat treat deserves a note of its own on steel parts. If the part is hardened after machining it may move, so critical features get finished afterwards by grinding. That is a second process on a second machine and it shows up in the price.

Four changes that bring a quote down

Open the tolerances that do not matter. Look at every callout and ask what fails if it drifts. Most drawings tighten everything out of habit.
Shrink the billet. Losing 10 mm of height across a part can drop you into a smaller stock size and cut a roughing pass.
Round the internal corners. A 3 mm internal radius lets a shop use a bigger, faster cutter. A sharp internal corner means either a tiny tool or a second operation.
Order the quantity you will actually use. Not the quantity you need this week.

What to send so the quote is real

Shops price what they can see. Send a STEP file for the geometry and a PDF drawing for the tolerances, materials, finish and thread callouts. If you only have the old part, photograph it with a ruler in frame, measure the features that mate with something else and say what it bolts to.

A quote built on a clear drawing is a quote the shop can stand behind. A quote built on a photo and a hope carries a margin for everything the shop could not see.

Frequently asked questions

Why is one piece almost as expensive as ten?

Because programming, fixturing and the first proving cut are paid once per order, not once per part. Those hours sit on the invoice whether you order one piece or ten, so ten pieces cost far less each.

Does sending a STEP file make the part cheaper?

It makes the quote faster and more accurate, which usually means less padding. A shop working from photos alone has to guess, and guesses get priced with a margin for error.

Is it cheaper to have one shop do everything?

Usually yes, if the shop already has its plating and anodizing vendors. Splitting the job yourself adds freight, a second inspection and a gap where nobody owns the result.

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