Aluminium is the most commonly milled metal, and for good reason. It cuts easily, is light, conducts heat well and finishes nicely with anodising or bead blasting. Housings, brackets, base plates, heat sinks and fixtures are therefore often milled from a block of aluminium.
Makernaut has CNC machining carried out by selected partners. You send your file and drawing; we handle the quote, production and follow-up. You get your quote within one working day.
Which aluminium alloy should you choose?
Aluminium is rarely pure: it's an alloy, and the choice sets strength, corrosion resistance, weldability and how well the part anodises. Three alloys come up most often in Europe.
| Alloy | Strength | Corrosion | Welding | Anodising | Choose it for |
|---|---|---|---|---|---|
| 6082 | Good | Good | Good | Good | General structural parts, brackets, housings |
| 7075 | Very high | Moderate | Not recommended | Good, less decorative | Highly loaded, lightweight parts |
| 5083 | Moderate | Very good, including seawater | Very good | Possible, less decorative | Base plates, marine and welded parts |
The table is a qualitative comparison based on the usual properties of these alloys. Exact values depend on the temper and the supplier's datasheet.
- Choose 6082 if you have no special requirements. It's the safe default: machines well, anodises well and is widely available.
- Choose 7075 when strength-to-weight is decisive, as with drones, robot arms or sports equipment. It costs more and resists corrosion less well.
- Choose 5083 for damp or salty environments and for parts that will be welded. It's softer, which makes milling fine details harder.
Not sure? Tell us what the part has to withstand and we'll suggest an alloy.
Design rules for milled aluminium
A cutter is round and has a limited length. Almost every design rule follows from that. Keep it in mind and you get a part that's quicker, and so cheaper, to make. The values below are common rules of thumb, not hard limits.
Internal radii
An internal pocket corner can never be sharp: the cutter always leaves its own radius. Draw the internal radius slightly larger than the cutter radius so it can move smoothly through the corner. A rule of thumb is a radius of at least a third of the pocket depth. If you need a sharp corner for a square part, add a relief in the corner (a dog-bone).
Pocket depth
The deeper a pocket, the longer the cutter and the more it vibrates. As a rule of thumb, a pocket stays comfortable to mill up to about three to four times the cutter diameter. Deeper, narrow pockets are possible but need special tooling and more time.
Wall thickness
Thin walls deflect and vibrate during milling, which hurts accuracy and surface finish. Keep walls as thick as your design allows, especially tall ones. A tall, thin wall is harder than a low wall of the same thickness.
Threads
- Use standard metric sizes (M3, M4, M5…) so standard tooling will do.
- A thread depth of about one and a half to two times the diameter is usually enough; going deeper adds little strength.
- Will a screw be undone and refitted often? Consider thread inserts, as aluminium threads wear faster than steel.
- Mark threads on the drawing: in a STEP file a hole is often just a cylinder.
Tolerances only where needed
Tight tolerances take time: slower machining, extra measuring and sometimes an extra set-up. So only specify them on functional faces, such as fits for bearings, pins or mating parts. Elsewhere a general tolerance is enough, for example to ISO 2768. The CNC machining service page shows what our partners' machines achieve.
Finishing: anodising and blasting
- As machined: the tool marks stay visible. Fine for internal parts and prototypes.
- Blasting (for example with glass beads): an even, matt surface that hides tool marks and small scratches.
- Anodising: a hard oxide layer that protects the surface, natural or coloured. Hard anodising gives a thicker, wear-resistant layer.
- Blasting followed by anodising is a popular combination for visible parts with a clean, matt look.
Note: anodising adds a thin layer. Mark on the drawing which fits and threads need masking.
What drives the price of milling aluminium?
There's no fixed price per cm³ for CNC machining. The price depends mainly on machine time and preparation. These are the biggest factors:
| Factor | Why it matters | How to keep it in check |
|---|---|---|
| Number of set-ups | Every time the part is flipped takes time and a new reference. | Design so as much as possible can be milled from one or two sides. |
| Material | The alloy and the size of the raw block set the material cost. | Choose 6082 unless you really need the properties of 7075 or 5083. |
| Tolerances and surface | Tight tolerances and fine roughness mean slower machining and more checking. | Specify them only where functionally needed. |
| Geometry | Deep pockets, small radii and thin walls need smaller tools and more time. | Follow the design rules above. |
| Quantity | Programming and set-up are one-off costs spread over the batch. | Order a few extra if you know you'll need them. |
| Finishing | Blasting, anodising and masking are extra steps. | Only finish the visible or functional parts. |
What to send for a quote
- A STEP file of the part, modelled in millimetres.
- A technical drawing (PDF) with tolerances, threads and finish.
- The alloy you want, or what the part needs to do.
- The quantity.