CNC milling

CNC milling is a machining process in which a rotating cutting tool (a milling cutter, such as an end mill) removes material from a workpiece through controlled motion of the CNC machine's axes. Unlike turning, where the workpiece rotates, in milling the tool rotates and moves relative to the workpiece in space.

Milling can produce flat faces, pockets, slots, freeform surfaces and very complex 3D geometry (on 5-axis machining centers). It is a core process for making machine components, molds, jigs, fixtures and tools from metals (aluminum, steel, stainless steel, titanium) or engineering plastics.

The basic milling operations are face milling (flat surfaces), pocket milling, contour milling (2.5D profiles), 3D milling (freeform surfaces, for example for molds), thread milling and drilling. 5-axis machining centers can handle very complex geometry in a single setup.

The accuracy of CNC milling depends on the machine, the tool, the workholding and the material. Everyday work typically achieves ±0.01 to ±0.05 mm. Tighter tolerances require calibration, thermal stabilization and special procedures. For the most precise surfaces, milling is combined with grinding.

CNC milling suits prismatic (non-rotational) metal and plastic parts: plates, flanges, brackets, housings, covers, frames, fixtures, molds and EDM electrodes. It is used for one-off prototypes as well as production series, especially when a part needs accurate flat faces, precise hole positions or freeform surfaces.

For prototypes, milling from solid stock (for example aluminum or POM, also known as acetal) is a common alternative to 3D printing when you need the real material, higher accuracy or a better surface finish.

The design has to respect the shape of the tool. Internal pocket corners always have a radius at least equal to the cutter radius, and deep, narrow pockets require long tools that deflect and cut slowly. Thin walls chatter and deform during machining. Every side of the part that has to be reached usually means another setup and a higher price.

In your request for quote, state the material, general tolerances, surface roughness requirements for functional faces, deburring and surface finishing. Ask whether the shop machines on a 3-axis or a 5-axis machine, because that affects the number of setups, the accuracy of feature-to-feature positions and the price.