Cheap CNC machining: 5 affordable options that hold tolerance

Most quotes are dominated by setup, not by spindle hours. A part that needs three setups on a 3-axis mill carries three fixture builds, three zeroing steps, and three chances for stack-up error. Move the same geometry to a 4-axis or 5-axis machine and one setup often covers what took three.

We run 16 simultaneous 5-axis centers and 12 four-axis mills. For a bracket with features on five faces, the 5-axis route is usually cheaper even though the hourly rate is higher. The saving is in labor and fixturing, not in the cut.

There is a limit. Tiny parts with one flat face and two holes do not benefit from 5-axis. On those, a three-axis machine with a soft jaw is faster, and cheaper. If your part fits in a 500 × 310 × 200 mm envelope and has features on two faces, ask for the 3-axis price first.

Ask your supplier how many setups they quoted. If the answer is vague, the price probably has hidden setup in it.

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  One setup beats three5-axis handles five faces without re-clamping.
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  Fixture cost is realA custom fixture can add more than the machining.
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  Small flat partsStay on 3-axis; 5-axis adds no value.

Aluminum 6061-T6 cuts about three times faster than 304 stainless at the same surface finish. On a 500-part run, that gap is the single largest line item after material cost itself. If the drawing says 304 because the last project used 304, re-check whether 6061 or 7075 meets the load case.

Titanium TC4 (Ti-6Al-4V) and Inconel cost more per kilo and cut slowly. They are correct for high-temperature and high-strength parts. They are the wrong answer for a sensor housing that never sees 80 °C.

Plastics are the cheapest route when the part does not carry load. POM and ABS machine fast and hold decent tolerance; PEEK costs far more and is only worth it for chemical or thermal resistance.

Material substitution is a design decision, not a purchasing one. Get your stress engineer to sign off before you ask for the cheaper alloy.

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  6061-T6 firstFast cutting, good strength, wide stock availability.
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  304 only when neededCorrosion resistance has a real machining cost.
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  PEEK is not cheapUse it for temperature or chemistry, not for looks.

A ±0.005 mm callout on every dimension multiplies inspection time. If a bore locates a bearing, hold it tight. If a clearance hole passes a screw, ±0.1 mm is fine and costs less to verify.

We see drawings where the title block says ±0.005 mm and the part is a cover plate. That single line can add 20 to 30 percent to the price because every feature now needs a CMM report. Mark critical dimensions and leave the rest general.

Surface finish works the same way. Ra 0.2–0.8 μm needs extra passes and sometimes polishing. Ra 1.6–3.2 μm is the natural as-machined result on most aluminum parts. Specify the fine finish only on sealing faces and sliding surfaces.

One more: deep holes, thin walls, and sharp internal corners raise cost more than tight tolerance does. A 0.5 mm internal corner radius forces a small tool that breaks easily and cuts slowly. Open it to 1 mm or the tool radius your supplier names and the price drops.

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  Mark only critical dimsGeneral tolerance covers the rest.
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  Ra 1.6–3.2 μm is defaultFine finishes cost extra passes.
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  Open internal cornersSmall end mills cut slowly and break.

CNC is not always the cheapest route at every volume. For 1 to 50 parts, machining wins on lead time and accuracy. Above a few thousand identical parts, die casting or vacuum casting can beat it on unit price, though tooling adds cost and time up front.

3D printing sits between them. A printed prototype in a few days costs less than a machined one and lets you check fit before you commit to metal. We run both, so we can tell you which route fits your geometry rather than which one we prefer to sell.

Sheet metal fabrication is the cheap answer for enclosures and brackets under 3 mm thick. Laser cutting plus bending is faster and cheaper than milling a box out of solid stock. If your part is essentially a folded panel, do not machine it.

The decision rule is simple. Few parts and tight tolerance: machine. Many parts and moderate tolerance: cast. Thin and flat: sheet metal. Prototype for fit only: print.

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  1–50 partsCNC gives the best accuracy per dollar.
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  1,000+ partsCasting can lower unit price after tooling.
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  Thin panelsSheet metal beats milling solid stock.

Buying a used mill and running parts in-house looks cheap on the invoice. Add tooling, coolant, a cam programmer, floor space, and the learning curve on the first ten jobs, and the real number is higher. That math only works when you have steady volume and someone who can run the machine.

An online quotation service removes the capital cost. You upload a STEP file, get DFM feedback and a price, and pay per part. No machine payment, no idle time between jobs, no maintenance schedule. For teams without a machine shop, this is the lowest-risk path to a metal part.

Confidentiality matters here. We work under NDA on request and treat uploads as confidential. If your part is patent-pending or under a customer agreement, ask for the NDA before you send files.

The trade-off is control. You do not see the setup or choose the tool path. That is why the DFM report matters. Read it, fix the flagged features, and the second quote usually comes back lower than the first.

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  No capital costPay per part instead of per machine.
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  DFM firstFix flagged features before you order.
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  NDA on requestProtect design files before upload.