Which CNC machining material should your part be made in?

For most CNC machining, aluminium 6061 is the right material: light, rust-free, quick to cut and easy to anodise. Move to steel for hardness and wear, stainless steel for wet places, brass for fittings, titanium when a light part must be very strong, magnesium when it must be as light as possible, a plastic for low friction or insulation, and teak, walnut or oak for a real wood finish.

We machine all of these in Singapore as part of our CNC machining service. If you are new to the process, start with what CNC machining is and when to use it.

CNC machining materials at a glance

Accuracy: down to ±0.05 mm on the dimensions you mark. Lead time: about 5 to 7 working days for a part about 10 to 15 cm across, as a rough guide; check with us for bigger parts or a deadline.

Know your material? Send the file for a quote

Aluminium 6061 and 7075: the right start for most metal parts

Aluminium is much lighter than steel, does not rust, and cuts quickly and cleanly, which keeps machining time down. It is also the metal that anodises best (see finishes below).

• 6061 is the all-rounder. It resists corrosion well, welds easily and machines to a clean finish. Use it for brackets, fixtures, enclosures and prototype housings.
• 7075 is much stronger and harder, so it suits a light part that has to carry a heavy load, such as a high-stress bracket or a part in a moving machine. It is not usually welded.

If you are unsure, start with 6061 and tell us the load. We say so if the part needs 7075.

Ask whether your part needs 6061 or 7075

Steels: for hardness, wear and welded frames

Steel is heavier than aluminium but harder and tougher. We machine three kinds:

• S45C medium carbon steel is stronger than mild steel and machines well. It is the usual choice for shafts, pins, gears and other parts that turn or take a knock.
• Q235 mild steel is the most widely used steel. It is easy to weld and bend, so it suits base plates, brackets and frames.
• D2 tool steel is very hard and resists wear, so it is used for punches, wear plates and cutting edges. That hardness makes it slow to machine.

Plain steel rusts, so S45C, Q235 and D2 need a coating or oil unless they live somewhere dry. Ask us about a finish that suits where the part will be.

Not sure which steel? Tell us what the part does

Stainless steel 304 and 316: for wet places and food or lab use

Stainless steel resists rust without a coating, which makes it the metal for anything wet, washed or near food.

• 304 is the everyday stainless. It resists rust well indoors and in the open, is tough, and is not magnetic. Use it for housings, food and kitchen parts, and lab fixtures.
• 316 resists corrosion even better, especially against salt water, chemicals and harsh cleaning. Choose it for marine fittings and chemical or lab parts.

Both are tougher to cut than aluminium, so machining takes longer.

Ask whether your part needs 304 or 316

Brass: for fittings, valves and a gold look

Brass is one of the easiest metals to machine: it cuts cleanly into fine threads and small details. It resists corrosion and wear, and its warm gold colour is often part of the design. Use it for fittings, valves, small hardware, decorative trim and badges. It is heavy for its size, so it is not the metal for a part that must be light.

Send your brass part for a quote

Titanium and magnesium: when a part must be light and strong

• Titanium alloy is strong, light and resists corrosion, including salt water. It suits parts that must be both light and strong. It is slow to machine and costs more than the other metals here, so choose it when nothing lighter will do the job.
• Magnesium alloy is the lightest metal we machine, lighter than aluminium. It damps vibration and spreads heat well, which suits light housings and frames. It needs a protective finish in most places, so ask us about one.

For a light metal part with a shape too complex to cut, our guide to metal 3D printing versus CNC machining weighs the two routes.

Ask whether titanium or magnesium suits your part

Plastics: for light, low-friction or insulating parts

A machined plastic part is solid all the way through, with no layers, so it is stronger and more even than a printed one. Each plastic has its own job:

• POM (Delrin, acetal) is the all-round machining plastic: stiff, slippery and steady in size. Use it for gears, bushes, slides and lids.
• Nylon (PA6) is tough and resists wear. It suits wear pads, rollers and guides, but it takes up a little moisture, so its size can change slightly.
• PTFE is very slippery and resists almost any chemical. It suits seals, washers and parts that touch chemicals. It is soft, so fits are looser.
• ABS is the tough everyday plastic for covers, housings and prototypes. It paints well after a primer.
• Acrylic (PMMA) is clear and glossy for windows, light guides and display parts. It can crack if knocked.
• PC (polycarbonate) is very tough and takes more heat than ABS or acrylic. It suits guards and clear covers.
• PP (polypropylene) is light, flexible and resists chemicals, so it suits chemical-facing parts and hinges that flex. It is hard to glue.
• Bakelite is hard, resists heat and does not conduct electricity, so it is used for jigs and insulating parts. It is brittle if knocked.

Read how we made it in the POM fuel filling lid project.

Not sure which plastic? Tell us what it touches

Hardwoods: teak, walnut and oak for a real wood finish

A CNC machine cuts hardwood cleanly, so casings, bases and display pieces come out with clean edges and a real grain.

• Teak is oily and stands up to damp, so it suits pieces near water or outdoors.
• Walnut is dark with a fine grain, the usual pick for premium product casings and bases.
• Oak is hard and strong with an open grain, good for bases and fixtures that take handling.

Wood moves a little as the air gets wetter or drier, so leave room in any fit.

Send your wooden part for a quote

Finishes: anodising and bead blasting; ask us for the rest

• Anodising adds a hard, coloured layer to aluminium. Black is the colour we are asked for most. Titanium can be anodised too; we have made titanium parts anodised in gold.
• Bead blasting gives an even matt surface and hides fine tool marks. It is often done before anodising.
• As machined is a clean finish in its own right, and the right choice for most plastic parts.

For plating, brushing or any other finish, ask us and we confirm what suits your material. A finish adds time to the job.

Ask us about a finish for your part

Still not sure? Start from what the part has to do

Tell us four things: what the part does, what load it takes, where it lives (dry, wet, hot, outdoors) and how it must look. That is usually enough for us to suggest a material. If the part could also be printed, our materials guide covers the 3D printing side. Our studio is at 994 Bendemeer Road, Singapore.