How does CNC milling work and what shapes can it produce for metal parts?

Quick Answer

CNC milling works by moving a rotating cutting tool along programmed toolpaths to remove material from a stationary workpiece. It can produce virtually any 2D or 3D shape: flat surfaces, square and round pockets, slots and keyways, threaded holes, contoured surfaces, complex 3D profiles, and precision features like undercuts and thin walls. Five-axis milling can even reach around corners to machine complex organic shapes in a single setup.

How CNC Milling Works

A CNC milling machine holds the workpiece on a table while a rotating spindle moves the cutting tool along programmed X, Y, and Z axes. The CAM software generates toolpaths that tell the machine exactly where to cut, how fast to move, and how deep to go. The cutting tool (end mill, ball mill, drill, or tap) rotates at speeds from 1,000 to 20,000 RPM while traversing across the workpiece, removing material in thin layers.

What Shapes Can Be Produced

3-axis milling produces flat surfaces, pockets, slots, drilled and tapped holes, and simple 2.5D profiles. 4-axis milling adds rotary motion for helical features, cylindrical cam profiles, and parts requiring indexing. 5-axis milling enables complex 3D surfaces, turbine blades, impellers, molds, dies, and undercut features -- all in a single setup, reducing lead times and improving accuracy.

Machinable Part Features

CNC milling can achieve: minimum wall thickness of 0.020" (0.5 mm) in metals, internal corner radii as small as 0.010" (0.25 mm) with small end mills, hole diameters from 0.005" (0.13 mm) to several inches, threads as fine as #0-80 UNC, surface finishes down to 16 Ra, and tolerances as tight as ±0.0005" on precision machines.

Why Choose SOMI Custom Parts

At SOMI Custom Parts, we operate 30+ CNC milling centers including 3-axis, 4-axis, and 5-axis machines capable of handling parts from 10 mm to 2000 mm. Our programmers use advanced CAM software to optimize toolpaths for the best balance of speed and quality. Whether you need simple 3-axis brackets or complex 5-axis aerospace components, SOMI has the equipment and expertise to deliver precision-milled parts on time.

Case Study

A robotics company needed complex aluminum chassis with 5-axis contoured surfaces, precision bearing pockets, and threaded mounting holes across six faces. SOMI programmed the part for a single 5-axis setup, eliminating 3 separate fixturing operations. The result: 30% faster production, tighter feature-to-feature tolerances, and 100% first-pass yield across a 2,000-unit production run.

Industry Data

According to the 2025 International Manufacturing Technology Show report, 5-axis CNC milling machines now account for 28% of new machine tool sales, up from 15% in 2020. Companies using 5-axis milling report an average 40% reduction in setup time and 25% improvement in part accuracy compared to multi-setup 3-axis machining.

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