Custom Housing Parts CNC Machining: How to Choose a Supplier
This guide is for engineers and buyers sourcing enclosures, covers and housings that must fit a PCB, a sensor or a gearbox. It covers the checks that actually change the outcome: tolerance, wall thickness, finish, material, MOQ and certification. Read it before you send an RFQ.
In this article
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Key takeaways
What separates a machining supplier from a broker
Use this table when two quotes look similar on price.
| Check | Direct machine shop | Broker or trading company |
|---|---|---|
| Machine list | Names 5-axis, mill-turn, max travel | Says 'advanced equipment' |
| DFM feedback | Returns marked-up drawing in 12 hours | Forwards your file and waits |
| Tolerance reply | States a number for your feature | Repeats your drawing tolerance |
| Certificates | ISO 9001, IATF 16949, ISO 13485 on file | Borrows a partner's certificate |
| Material trace | Mill cert available on request | Rarely available |
| Setup disclosure | Number of setups and fixtures listed | Not listed |
| Inspection | 100% before shipment, reports on request | Vague, 'we check quality' |
| Change response | Engineer answers the phone | Sales only |
The short version
Send a drawing with datums and split tolerances, ask the shop to name the machine and the certification, and approve a first article before the batch. Do that and most housing problems never reach the assembly line.
What tolerance does custom housing parts CNC machining actually hold?
A housing is a fit problem, not a shape problem. The bore that holds a bearing, the pocket that seats a PCB, the face that mates with a gasket: those features set the tolerance budget. Everything else can be looser. GreatLight machines to ±0.005 mm (±0.0002 in) on critical features, but applying that number to a 300 mm outer profile adds cost without adding function.
Split your drawing into two groups before you send it. Critical features get a tight callout and a datum scheme. Cosmetic and clearance features get a general tolerance note in the title block, typically ±0.1 mm or ±0.2 mm. Shops quote the tightest number they see, so a loose part with one stray tight callout gets priced like a precision part.
Thin walls are the second trap. A 1.2 mm aluminum wall can be machined, but it will chatter if the shop takes a heavy pass. Ask how the wall is supported. On 5-axis work with a Ø400 mm rotary table, thin walls are usually finished with light radial passes at high spindle speed rather than one deep cut.
Datum choice matters more than most engineers expect. If the PCB mounting face is your A datum, say so. If the shop picks a different datum, the housing will pass inspection and still not fit the assembly. Put the datum callout on the drawing, not in an email.
- 1Tight where it fitsBearings, seals, connector openings, mating faces.
- 2Loose where it showsOuter profile, non-mating ribs, cable exit areas.
- 3Name the datumThe assembly face should be A, not whatever is convenient to clamp.
- 4Flag thin wallsAnything under 1.5 mm in aluminum or 1.0 mm in plastic.
Material and finish choices for housing parts
Aluminum covers most housings. 6061-T6 machines cleanly, takes anodizing well and has enough stiffness for a wall around 2 mm. 7075 is stronger but anodizes to a darker, less uniform color, so it suits brackets more than visible covers. If the housing is die-cast in volume, ADC12 is the usual alloy and the CNC step becomes a finishing operation on the casting.
Stainless enters when the housing sees washdown, salt spray or sterilization. 303 is the free-machining grade and the cheapest to cut. 316L is the choice for medical and food equipment. 17-4PH (SUS630) gives high strength after heat treatment and is common on valve and pump housings. Expect longer cycle times and more tool wear than aluminum.
Plastics show up in prototypes and low-volume electronics enclosures. ABS and PC machine easily; POM holds a thread well; PEEK survives high temperature but costs far more. Carbon fibre reinforced stock machines with sharp tooling and dust extraction, and it will dull a cutter faster than any metal on this list.
Finish is a specification, not a decoration. Anodizing adds 5–15 μm per surface, which changes a press-fit bore. Hardcoat anodizing adds more and can be 25 μm or thicker. If a bore must stay at size after coating, machine it undersize and let the coater bring it back, or mask the bore. Tell the shop the finish before machining starts, not after.
- 16061-T6Default for machined aluminum housings.
- 2316LMedical, marine and washdown environments.
- 3ADC12Die-cast housing bodies finished by CNC.
- 4PEEKHigh-temperature or chemically aggressive service.
How to check a custom housing parts CNC machining supplier
Start with the machine list. A housing with deep pockets on five faces needs a 5-axis center or a mill-turn machine. A 400 mm long housing needs travel to match; GreatLight runs up to 4,000 mm maximum processing size, with 16 simultaneous 5-axis centers and 16 mill-turn centers in the shop. If a supplier cannot name the machine that will cut your part, they are not cutting it.
Then check certification against your industry. ISO 9001:2015 is the baseline. Automotive programs usually require IATF 16949:2016. Medical device housings require ISO 13485:2016, and ISO 27001:2022 covers information security for customer drawings and CAD data. Certificates should be current and issued to the company you are paying, not to a sister company.
Ask about inspection. A supplier that inspects 100% before shipment and can send dimensional reports is different from one that samples. For a housing, the critical checks are bore diameter, pocket depth, hole position and flatness of the mating face. First article inspection on the first part of a run is normal practice; ask for it in writing.
Finally, test the communication before you place the order. Send a drawing with one deliberate ambiguity and see what comes back. A shop that returns a marked-up drawing with questions in 12 hours will catch problems in production. One that says 'no problem' to everything is telling you they did not read it.
- 1Machine fit5-axis or mill-turn for multi-face housings.
- 2Certificate matchISO 13485 for medical, IATF 16949 for automotive.
- 3Inspection plan100% before shipment, reports on request.
- 4Communication testAmbiguous drawing in, useful questions back.
Cost, MOQ and lead time: what actually moves the number
Machining has no tooling cost, so there is no minimum order quantity to amortize. One prototype and a 10,000-part run use the same setup. What changes is the per-part price: setup time is spread over more parts. This is why a single housing prototype costs far more per unit than the hundredth part, and why a supplier that demands a large MOQ is often a casting or molding shop, not a machine shop.
The biggest cost levers on a housing are the number of setups, the tolerance class and the finish. A part that can be cut in two setups is cheaper than one needing five. A ±0.005 mm bore costs more than a ±0.05 mm bore. A hardcoat anodized surface costs more than as-machined. If a quote comes in high, ask which of these three is driving it before you ask for a discount.
Lead time has two parts. The first is the quote and DFM turnaround, which should be within 12 hours. The second is production. Once the drawing is frozen and material is in stock, machining can start within 24 hours and parts ship in 3–5 days for typical housing sizes. Large 4,000 mm parts and exotic alloys take longer because stock has to be sourced.
Risk sits in the changes. A housing revision after machining starts means scrapped parts. Freeze the drawing, run a first article, then release the batch. If you expect revisions, prototype first and treat the production run as a separate order.
- 1SetupsFewer setups, lower price.
- 2Tolerance classReserve ±0.005 mm for features that fit something.
- 3FinishHardcoat and masked bores add steps and cost.
- 4RevisionsEvery post-release change risks scrapped parts.
Step by step: from drawing to shipped housing
Follow this order to avoid the common rework loops.
- 1Send the 3D model and a 2D drawingSTEP or IGES plus a PDF with datums, tolerances and finish notes. A model alone leaves the tolerance open to interpretation.
- 2Wait for DFM feedbackThe shop should return a marked-up drawing within 12 hours, flagging thin walls, deep pockets and features that need a special cutter.
- 3Freeze tolerance and finishConfirm which features are critical and which are general. Confirm the finish and whether any bore must be masked before coating.
- 4Approve material and stock size6061-T6 plate, 316L bar or ADC12 casting. Stock size affects how many parts come from one blank and therefore the price.
- 5Run a first articleCut one part, inspect it fully, compare against the drawing and the mating assembly. Do this before the batch, not after.
- 6Release the production runWith the first article approved, machining can start within 24 hours and typical housing batches ship in 3–5 days.
- 7Inspect before shipment100% inspection with reports on request. Check bore diameter, hole position and mating face flatness first.
Questions buyers ask before ordering housings
What file formats do you need for a housing quote?
A STEP or IGES model for geometry, plus a 2D PDF drawing for tolerances, datums and finish notes. If you only have a model, we can quote it, but we will ask which features are critical before machining.
Native CAD is welcome but not required. Send the files through the secure upload on the quote page; uploads stay confidential and an NDA is available on request.
Can you machine a housing from a casting?
Yes. Die-cast ADC12 housings are commonly fixtured and CNC machined on the mating faces, bores and threads. The casting holds the general shape and the machining brings critical features to size.
This is usually cheaper than cutting the whole housing from solid once volumes pass a few hundred parts, because less material is removed.
How thin can a housing wall be?
In aluminum, 1.2–1.5 mm is practical for a supported wall. Below that, deflection during clamping and chatter during cutting become the limiting factors, not the cutter.
In plastics, 1.0 mm is workable with light passes. If the wall is long and unsupported, add a rib or accept a looser tolerance on that wall.
Do you offer surface finishing in house?
Anodizing (clear, color, hardcoat, conductive), electroless nickel, zinc, silver and gold plating, powder coating, black oxide, bead blasting, tumbling, brushing and polishing are all available, along with laser marking at a minimum character height of 1.5 mm.
Tell us the finish before machining. Coating thickness changes bore sizes, and masking decisions are made at the machine, not at the coater.
What is the smallest order you accept?
There is no minimum order quantity. One prototype and a 10,000+ part run are both normal.
The per-part price drops as quantity rises because setup time is spread across more parts, not because tooling is amortized.
Which certifications apply to housing work?
ISO 9001:2015 is the baseline quality system. Automotive housings typically fall under IATF 16949:2016, and medical device housings under ISO 13485:2016.
ISO 27001:2022 covers information security for drawings and CAD data. Tell us your industry at the RFQ stage so the correct documentation is attached.
Send your housing drawing for a DFM review
Upload a STEP file and a 2D drawing. You get a quotation and a free DFM analysis within 12 hours, with the machine, setup count and tolerance notes spelled out.
12-hour quoteNo MOQ100% inspectionNDA on request
More from the shop floor
We publish setup notes, tooling trials and inspection data from the factory floor.
