Aluminum CNC Machining: Grades 6061/7075, Tolerances & When to Choose It

Aluminum is the most machined metal in custom part work for a reason — it cuts fast, holds tight tolerance, anodizes cleanly and weighs a third of steel. Here is how to pick the grade, what tolerance to expect, and the design rules that keep an aluminum part cheap and accurate.

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Why Choose Aluminum for a CNC Part

Aluminum machines faster than steel with less tool wear, so cycle time and tooling cost both drop — and because it is light and dimensionally stable, it holds tight tolerance without the heavy clamping steel needs. For brackets, housings, fixtures, heatsinks and most prototypes it is the default choice. Where the part needs steel's hardness or load capacity, our materials overview compares the families. See the full numeric grade picture in the aluminium grade chart.

Grade	Machinability	Strength	Notes	Typical use
6061-T6	Excellent	Good	Weldable, anodizes well	Brackets, housings, fixtures
7075-T6	Good	Very high	Less corrosion resistant, hard to weld	Aerospace, high-load parts
6082	Excellent	Good	EU equivalent of 6061	General EU-sourced parts
2024	Good	High	Poor corrosion resistance	Structural, aircraft
5052	Fair	Moderate	Best corrosion resistance	Marine, enclosures
MIC-6 (cast plate)	Excellent	Low	Stress-relieved, very flat	Bases, plates, jigs

Custom aluminum 6061 manifold block housings — CNC milled with drilled, tapped and reamed features for fluid handling assemblies — **Typical 6061 aluminium housings** — milled, drilled and tapped in one setup on our 3-axis VMCs. See the full CNC milling service for tolerance, surface finish and lead-time details.

CNC machined aluminium valve housings — 6061 milled bodies with drilled and tapped ports — **Aluminium valve housings**
6061 milled bodies, drilled and tapped ports. See CNC milling.

Grid of precision CNC machined aluminium parts — brackets, fittings and small housings — **Precision aluminium parts**
Brackets, fittings and small housings in 6061/7075.

Tolerances and Surface Finish on Aluminum

Aluminum is predictable, which is why it machines to tight tolerance more easily than many steels: routinely ±0.025 mm, and ±0.01 mm on critical features with a controlled setup. The full table and the cost curve behind it are in our tolerance chart. For appearance or corrosion resistance, anodizing is the standard finish — Type II for color, Type III (hardcoat) for wear. Remember anodizing adds a few microns, so a bore or shaft that must fit after coating should be called out at finished size with the layer accounted for (or masked).

Which Process

Most aluminum parts are milled; round ones are turned. For parts with angled features or multiple faces, 5-axis machining reduces setups and keeps critical relationships true. Aluminum's speed makes it ideal for both one-off prototypes and low-volume runs. If you're weighing aluminium against stainless or titanium, our three-material comparison lays out the strength, machinability and cost trade-offs. Aluminium is also the default material for machined electronics enclosures — our guide to CNC machining electronics enclosures covers the wall-thickness, EMI-groove and thread rules that keep a box from warping.

Design Rules That Keep Aluminum Cheap

Aluminum is forgiving, but a few rules still matter. Avoid very thin walls that chatter or deflect. Standardize thread sizes and hole diameters to off-the-shelf drills and taps. Only call out tight tolerance where the function needs it — over-specifying costs money for no benefit. The deeper version is in our cost-reduction guide and the GD&T guide for buyers. If you are weighing aluminum against printing for a low-volume part, the machining vs 3D printing comparison helps you decide.

Frequently asked

What is the best aluminum grade for CNC machining?

6061-T6 is the all-round default: easy to machine, weldable, anodizes well, and strong enough for most brackets, housings and fixtures. 7075-T6 is the choice when you need strength closer to steel at a fraction of the weight — but it is less corrosion resistant and harder to weld. 6082 is the European equivalent of 6061 and common in EU-sourced drawings. Pick the grade from the function, not the habit.

What tolerance can CNC machining hold on aluminum?

Routinely ±0.025 mm on a well-fixtured part, and ±0.01 mm on critical features with a controlled setup. Aluminum is stable and dimensionally predictable, which is one reason it machines to tight tolerance more easily than many steels. The numbers and the tolerance-cost curve are in our tolerance chart.

Can aluminum parts be anodized after machining?

Yes. Type II anodizing gives a decorative colored, corrosion-resistant layer; Type III (hardcoat) gives a thick, wear-resistant surface. Anodizing adds a few microns to dimensions, so if a bore or shaft must fit after coating, the drawing should call out the finished size and let the shop account for the layer — or mask the feature.

Is aluminum cheaper to CNC machine than steel?

Usually yes. Aluminum cuts faster, needs less tool wear, and holds tolerance with lighter passes, so cycle time and tooling cost drop. The material itself is also lighter and often cheaper per part. The trade is lower strength and hardness — so aluminum wins when the part does not need steel's load or wear properties.

Need a custom aluminum part?

Send the drawing and the grade. We'll mill or turn it to tolerance, anodize if you want, and flag any dimension that is tighter than the function needs.

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Related: Material Selection Guide