Custom CNC aluminum parts: how to choose a supplier you can actually work with

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  Key takeaways
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  What to weigh before you send an RFQ
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  Pick the alloy before you argue about price
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  Tolerance belongs on features, not on the whole drawing
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  Five-axis setups cut part count and error stacking
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  Finishing and inspection are where schedules slip
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  Order size, lead time and confidentiality
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  How to run a custom CNC aluminum parts order

Most custom CNC aluminum parts we quote come in through a 6061-T6 default. That is usually the right call. It machines fast, welds predictably, anodizes cleanly and holds ±0.005 mm on bores and faces without special fixtures. If your part is a bracket, a housing, a manifold block or a chassis plate, 6061-T6 is the baseline and anything else has to justify itself.

7075-T6 is the choice when strength-to-weight drives the design, such as drone arms, racing suspension links or structural plates. It cuts about 20–30% slower than 6061 and the chips are abrasive, so cycle time rises. The payoff is roughly double the yield strength. If your load case does not need that, you are paying for margin you will never use.

2024-T4 sits between the two on strength but is the least forgiving to machine. It has poor corrosion resistance on its own, so it usually needs anodizing or a conversion coat. 5052 and 5083 are for formed or welded parts where toughness beats stiffness. 6082 is the European near-equivalent of 6061 and behaves almost the same in the spindle.

ADC12 is a die-casting alloy, not a billet grade. If a quote lists ADC12 for a machined part, ask why. It machines to a duller finish and can show porosity when you cut into it. For prototypes that will later be die cast, machining from ADC12 stock is a reasonable way to test the shape, but do not expect the same surface quality as 6061.

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  Default to 6061-T6Fastest to machine, best finish, widest anodizing options.
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  Use 7075-T6 only for loadHigher strength, slower cutting, more tool wear.
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  Treat 2024 as a coating partPlan anodizing or conversion coating from the start.
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  Question ADC12 in a machined quoteIt is a casting alloy and can expose porosity.

A drawing stamped ±0.005 mm on every dimension is the single most common reason an aluminum quote comes back high. That tolerance is achievable, and we hold it daily on bearing bores, dowel holes and mating faces. Applying it to a 300 mm cosmetic edge or a non-critical clearance slot is wasted money.

The practical split is three tiers. Features that locate the part or carry a bearing get ±0.005 mm. Features that mate with another machined face get ±0.02 mm. Cosmetic and clearance geometry gets the general tolerance block, typically ±0.1 mm. Send a drawing with that split marked and the quote reflects the real work, not the worst case on every line.

Thin walls are the other cost driver. Below about 1.5 mm on an aluminum wall, the part starts moving under clamping pressure and cutting forces. We can hold 0.8 mm on short walls, but it needs light finishing passes, sharp tooling and often a support fixture. If the design allows 2 mm instead of 0.8 mm, take it. The part will be stiffer and cheaper.

Deep pockets matter too. A pocket deeper than about four times its tool diameter forces long-reach tooling, which deflects. Either open the corner radius so a larger cutter fits, or accept slower feeds and a higher price. The geometry fix is free. The machining fix is not.

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  Three tolerance tiers±0.005 mm on fits, ±0.02 mm on mating faces, ±0.1 mm general.
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  Watch walls under 1.5 mmThey deflect during clamping and need support fixtures.
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  Open deep pocket cornersA larger tool radius avoids long-reach deflection.

Every additional setup adds a datum transfer, and every datum transfer adds error. On a part with features on four sides, a three-axis route might need four fixtures and four setups. A simultaneous 5-axis center with a Ø400 mm rotary table can reach most of those faces in one or two setups, which is why the tolerance stack stays tighter and the lead time shortens.

That matters most for parts with angled ports, undercuts, sculpted surfaces or pockets that open on two planes. Those are the shapes where three-axis machining either cannot reach or needs an electrode and EDM step. If your part is a simple plate with drilled holes, a three-axis machine is the cheaper and faster answer. Match the machine to the geometry, not to the marketing.

Size sets the ceiling. Our largest travel is 4,000 × 400 × 150 mm, with medium envelopes at 750 × 1,150 × 550 mm and 600 × 600 × 600 mm. Long, thin aluminum parts in that top envelope are the hardest to hold flat, because the material moves as you remove it. Rough, stress-relieve, then finish. Skipping the middle step is how flatness fails.

Turned aluminum parts follow the same logic. Mill-turn centers handle a shaft with cross-drilled holes or milled flats without a second op, which removes a chucking step and the runout that comes with it.

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  Count your setupsEach one adds a datum transfer and error.
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  Five-axis for reachAngled ports, undercuts and sculpted surfaces.
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  Three-axis for simple platesCheaper and faster when the geometry allows.
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  Rough, relieve, finishLong thin parts will not stay flat otherwise.

Machining a part is only part of the route. Anodizing, plating, powder coating and laser marking are separate steps with their own queues. Clear and color anodizing change dimensions slightly, so if a bore has a ±0.005 mm fit, the anodize thickness has to be accounted for before the part is cut, not after.

Hardcoat anodizing builds a thicker oxide layer than decorative anodizing and will close a tight bore. Conductive anodizing is the option when the part needs masking for electrical contact. Laser marking needs a minimum character height of 1.5 mm to stay legible after coating. If your part number is small, cut it into the metal instead of marking it on top.

Inspection is the last gate. We check raw material on arrival, monitor in-process, and inspect 100% before shipment, with reports on request. For aluminum parts, that usually means dimensional checks on the critical features plus a visual pass for tool marks, burrs and coating defects. Ask for the report format you need before the run starts, not after.

The qualification rate we see on aluminum work is 99.99%, but that number only holds when the drawing is unambiguous and the tolerance tiers are realistic. When a drawing is vague, time goes into clarifying rather than cutting, and the schedule absorbs it.

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  Plan coating into the dimensionsAnodize adds thickness inside tight bores.
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  Masking for conductive anodizeTell us which surfaces must stay conductive.
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  1.5 mm minimum marked charactersSmaller text blurs under coating.
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  Agree the inspection report earlyFormat and features, before the run starts.

There is no minimum order quantity on our side, so a single prototype and a 10,000+ part run go through the same quoting path. That matters for aluminum because the first article often reveals a wall that is too thin or a pocket that needs a larger corner radius. Finding that out on one part is cheap. Finding it out on a production run is not.

The timeline we work to is a quotation and free DFM analysis within 12 hours, production starting within 24 hours, and parts shipping in 3–5 days. Those numbers assume the material is in stock and the drawing is final. If a grade has to be ordered or a tolerance needs a fixture that does not exist yet, the schedule moves. Ask which of the two you are in.

Confidentiality is a common blocker for custom CNC aluminum parts in aerospace and medical programs. Uploads stay secure and confidential, and an NDA is available on request. If your program requires one before you release drawings, say so on the first contact and it will not slow the quote down.

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  No minimum order quantityOne prototype or 10,000+ parts, same path.
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  12-hour quote and DFMFree DFM analysis with the quotation.
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  3–5 day shippingWhen material is in stock and the drawing is final.
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  NDA on requestRaise it before drawings are released.