What is CNC machining, and when should you use it?

CNC machining makes a part by cutting it out of a solid block of metal, plastic or wood, with spinning tools guided by a computer program. Use it when the part must be solid metal, fit to within a twentieth of a millimetre, or carry a clean machined surface; use 3D printing, sheet metal or moulding when it does not need to be.

CNC machining at a glance: what it makes and how long it takes

Lead time is a rough guide for a part about 10 to 15 cm across. Bigger parts and parts that need many setups take longer, so check with us.

Know it should be machined? Send the file for a quote

How CNC machining works: a cutter carves the part from solid

CNC stands for computer numerical control. A program written from your 3D file moves the tool, so the tenth part comes out like the first. Machining is the opposite of 3D printing: printing builds a part up, machining cuts it away.

Most of our work is milling: the block is clamped still and a spinning cutter moves over it, making flat faces, pockets, slots and holes for blocks, plates and brackets. Our mills are 3-axis: the tool moves left and right, forwards and back, and up and down. We also turn round parts, such as pins, discs and shafts, on request.

See what our CNC machining service covers

Materials: aluminium, brass, plastics and hardwoods

• Aluminium 6061 and 7075 for brackets, fixtures, enclosures and prototype housings. It is light, cuts cleanly, and can be anodised.
• Brass C360 for hardware, decorative trim and badges where the metal is part of the look.
• Delrin (POM) and nylon for low-friction wear parts and jigs: slides, bushes and guides.
• Teak, walnut and oak for product casings, bases and fixtures that need a real wood finish.

We pick the stock to suit both what the part has to do and how it has to look. For another material, send the drawing and we confirm whether we can cut it.

Not sure which material? Tell us what the part does

Tolerances: down to ±0.05 mm where you mark it

A tolerance is how far a size may be off and still be right. We hold down to ±0.05 mm on the dimensions you mark, and check the first part with digital calipers and pin gauges before making the rest. A 3D print is accurate to about ±0.3 mm on parts up to 100 mm, so a face that must fit is a machining job. Our guide to 3D print tolerances shows where that line falls.

Mark only the dimensions that matter: the hole a bearing presses into, a face that sits against another part, a hole for a pin. Tight tolerance on every edge adds time and cost without making the part better.

Have a fit that must be exact? Ask us about it

Cost and time: setups, tight tolerances and deep pockets add the most

CNC parts are priced per part, and the price follows the time on the machine. These add the most:

• Setups. Each time the part is unclamped, turned over and clamped again to reach another side is a new setup, with its own alignment and checks. A part cut from one side costs less than one cut from six.
• Tight tolerances. Every marked dimension means slower finishing cuts and more measuring.
• Deep, narrow pockets. They need a long, thin cutter that bends if pushed, so it has to cut slowly in light passes.
• Material. Aluminium, brass and plastics cut quickly; a tougher material has to be cut more slowly.
• Quantity. Programming and setting up are done once, so the cost per part drops as the batch grows. We make 1 to 50 parts; past that, ask about moulding.

See how our CNC parts are priced

Design tips: round inside corners and shallow pockets

• Inside corners come out rounded. The cutter is round, so a pocket’s inside corner keeps a curve the size of the tool. Draw a radius there, and if a square part must sit in it, add a small extra cut-out in each corner so its square edge has room. Outside corners can be sharp.
• Keep pockets shallow and wide. A deep, narrow slot needs a long, thin tool. Make it wider, or shallower, or open it to one side.
• Design for as few sides as you can. Put holes and pockets on the same face where the part allows it, so it is cut in fewer setups.
• Mark the tolerances that matter, not all of them. A note such as “±0.05 mm on the bearing hole, standard tolerance elsewhere” is enough.
• Avoid thin walls. A thin wall vibrates under the cutter and can bend. Leave some thickness, or ask us first.
• Send a STEP file. An STL is a mesh of triangles and machines poorly. Export STEP from your CAD program.

Send your design and we flag what will cost more

When to use something else: printing, sheet metal or moulding

• 3D printing wins when the shape has hollow insides, channels or lattices that no tool can reach, or when you want a cheap plastic test part in a few days. Many projects print a plastic version first to check the fit, then machine the final part. Get an instant price for a print.
• Metal 3D printing wins when the part must be metal and the geometry is too complex to cut. Our metal printing versus CNC guide weighs the two side by side.
• Sheet metal wins for thin enclosures, covers and bent brackets. Machining those from a solid block would turn most of it into chips. See sheet metal fabrication.
• Moulding wins when you need hundreds or thousands of the same part. See 3D printing, silicone moulding or injection moulding.

If you are unsure, send the file and say what the part does. We offer all of these, so we tell you honestly which one suits the part. Our studio is at 994 Bendemeer Road, Singapore.

Not sure it should be machined? Ask us