CNC Aluminum Service Guide

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  What matters most when sourcing aluminum parts
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  When aluminum CNC fits, and when another route wins
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  Pick the alloy from the load case, not from habit
• 4
  Match tolerance to the feature, not to the drawing border
• 5
  Finishes add material, so plan the mask before the cut
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  Read the quote for what it does not say
• 7
  7 checks to run before releasing the PO

Most aluminum parts we quote are 6061 or 6061-T6, and that is usually correct. It machines cleanly, welds, anodizes well and holds moderate tolerances without drama. The T6 temper gives roughly 276 MPa yield, which covers brackets, housings, manifolds and most fixture plates. A shop that pushes 7075 for every job is either reading your load case very carefully or padding the quote.

The exceptions are specific. 7075-T6 reaches about 503 MPa yield and is the right call for highly loaded aerospace fittings, racing suspension arms and tooling where stiffness per gram matters. It costs more per kilogram and cuts about 30 to 40 percent slower, so the part price moves with it. 2024-T4 is strong and fatigue resistant but has poor corrosion resistance unless it is clad or anodized. 5052 and 5083 are for formed sheet and welded tanks, not for tight-tolerance machining.

Small alloy changes can wreck a process. A 6063 extrusion looks like 6061 on a drawing but is far softer and gummier, so it tears instead of shearing and leaves built-up edge on the cutter. If your part starts life as an extrusion, tell the shop which temper and which standard you are buying to. ADC12 is a die-casting alloy, not a machining stock. Asking for it as a billet means someone will substitute something else.

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  6061-T6Default for structural brackets, housings and fixture plates.
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  7075-T6High load, weight sensitive parts. Expect a slower cycle and a higher price.
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  2024Fatigue critical, but anodize or clad it for corrosion.
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  5052 / 5083Sheet and weldments, not tight-tolerance turned parts.

A general tolerance block that says ±0.005 mm across the whole drawing is a claim nobody can meet on every feature. That number belongs on specific callouts: bearing bores, mating faces, dowel holes, spigots. On a 300 mm aluminum plate, thermal expansion alone moves the part about 0.007 mm for a 5 °C shop swing, so chasing microns across the full length is a losing argument. Put tight tolerance where the function lives.

Geometry decides which machine gets the job. A part with features on five faces and no good fixturing reference is a 5-axis job, and we run 16 simultaneous 5-axis centers for exactly that. A shaft with cross holes and a grooved profile is a mill-turn part. Simple plates with a few holes run faster on a 3-axis machine, and moving them there keeps the price down. The right question to a supplier is not "do you have 5-axis" but "which features need it".

Thin walls are the most common source of rework. Below about 1 mm, clamping pressure and cutter push-off both move the material, so the finished dimension drifts from the programmed one. The fix is sequence, not force: rough leaving 0.5 mm, stress relieve or let the part rest, then finish with light radial engagement. If your design has a 0.4 mm wall over a 100 mm span, expect to discuss a redesign rather than a tolerance waiver.

Anodizing is not a coating sitting on top of the metal. It converts the surface and grows outward, roughly half in and half out. Type II clear anodizing builds about 5 to 15 μm per surface. Hardcoat builds 25 to 50 μm and is much harder, which is why it is used on sliding surfaces and wear pads. That growth changes a bore diameter and a thread fit. A 6H thread that passes gauge before anodizing may not pass after it.

The engineering answer is masking, and masking has to be in the model or on the drawing before the part is cut. Threads, dowel holes, bearing seats and any press fit should be masked or the pre-plate dimension adjusted. Send the note with the RFQ, not after the parts come back undersized. We mask threads and bores on request, and laser marking with a minimum character height of 1.5 mm can go on a masked area or a machined pad.

Other finishes behave differently. Bead blasting gives a matte, uniform look and hides tool marks, but it slightly rounds edges, so it is a poor choice on a sealing face. Electroless nickel adds uniform thickness on complex geometry and is often used on aluminum where conductivity or solderability matters. Powder coating is thick, typically 60 to 100 μm, and will bridge small holes. Black oxide is for steel, not aluminum. Match the finish to the function and the stack-up, not to the photo in the catalog.

A useful quote has four things: a unit price with the quantity break, the alloy and temper in writing, the finish call, and a date tied to drawing approval rather than to the day you sent the RFQ. Quotes that arrive as a single number with no assumptions are hard to compare and easy to argue about later. We return a quotation and a free DFM analysis within 12 hours, and production can start within 24 hours of approval on stocked alloys.

Lead time is a chain, not a single number. Machining, anodizing, plating and inspection each have their own queue. Parts ship in 3–5 days on straightforward aluminum work, but a hardcoat line can add days on its own, and the historical late-delivery probability across our orders sits below 2 percent. When you compare two suppliers, compare the date they promise for the finished, inspected part, not the date they finish cutting.

Volume changes the economics but not the process. There is no minimum order quantity here, so one prototype and a 10,000-part run go through the same shop and the same inspection. On small quantities the setup, programming and fixturing dominate the price. On large quantities the material buy and the cycle time dominate. If a supplier's price barely moves between 1 and 1,000 pieces, ask what is missing from the small-quantity number.

Confidentiality is part of the package for aerospace, medical and automotive work. Uploads are secure and confidential, and an NDA is available on request before you send STEP files. If a supplier hesitates on a mutual NDA for a production program, that tells you something about how the relationship will run.