Manufacturing services · Chapter C · Method 13

CNC milling

Rotating cutters remove material from a fixed block under computer control. Used for master patterns, mould tools and finished parts.

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CNC spindle and cutter with coolant on a vertical machining centre. Representative process photo · Daniel Smyth · Pexels

Milling machine in use in the TCI workshop. TCI workshop

How it works

CNC milling, step by step.

A labelled schematic of the process (not to scale), and the four steps every job goes through.

Labelled diagram showing how cnc milling works — Schematic · not to scale. Drawn by TCI Group.

STEP 01

CAM

Programme toolpaths from the 3D model.

STEP 02

Fixture

Clamp stock in a vice or custom fixture.

STEP 03

Machine

Rough, then finish with smaller cutters.

STEP 04

Inspect & deburr

Break edges, deburr and measure.

Reference figures

What to expect.

Typical industry values to help you plan. We agree the figures for your part on the drawing.

Tolerance±0.13 mm metalsISO 2768 unless stated

Plastics±0.25 mmPlastics and composites

FinishRa 3.2 µmAs machined, or better

Form0.13 mm to 300 mmFlatness, parallelism

Materials	Aluminium, steel, stainless, brass, copper, titanium; plastics such as POM, nylon, PEEK, PTFE and acrylic; tooling board.
Finishes	As machined, bead blasted, anodised, powder coated, plated or polished.
Design guidance	Add internal corner radii slightly larger than the cutter. Keep pocket depth under about 4× cutter diameter. Call out only the tolerances that matter.
Best suited to	Mould tools, master patterns, brackets, housings and precision prototypes.
Watch-outs	Deep pockets and thin walls raise cost; sharp internal corners are not possible.

Other methods in CNC machining

Previous: Plastic extrusion Next: CNC turning

Next step

Not sure this is the right route?

Send a sketch, photo, sample or CAD file with your quantity and target date. We will recommend the most sensible route and explain the trade-offs before quoting.

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Reference figures are typical published industry values for planning, not a guarantee; final tolerances, materials and finishes are agreed in writing for each project.