CNC Machining Guide

What Is CNC Machining?

CNC (Computer Numerical Control) machining removes material from a workpiece using computer-controlled cutting tools. Multi-axis machines move tools and workpieces along programmed paths to achieve dimensional accuracy and repeatability that manual machining cannot match.

Common CNC Processes

Process	Best For	Typical Tolerance
3-Axis Milling	Prismatic parts, pockets, slots, faces	±0.02–0.05 mm
4-Axis Milling	Parts needing rotary machining on one axis	±0.01–0.03 mm
5-Axis Milling	Complex freeform geometries, turbine blades, impellers	±0.005–0.01 mm
CNC Turning	Cylindrical parts: shafts, bushings, flanges	±0.01–0.02 mm
Swiss Machining	Small, complex, high-volume precision parts	±0.005 mm

Design Considerations

• Avoid sharp internal corners — use internal radii of at least 1× tool radius
• Deep pockets increase cycle time; keep depth ≤ 4× diameter where possible
• Specify tolerances only where functionally required — tight tolerances add cost
• Design for the tool: standard hole sizes, standard thread depths
• Consider mirror-polished surfaces vs. standard finish for cost control

Surface Finishes

Finish	Ra Value	Typical Use
Machined as-is	Ra 3.2–6.3 µm	General industrial parts
Fine machined	Ra 1.6 µm	Sealing faces, visible parts
Precision ground	Ra 0.8 µm	Bearing surfaces, guides
Polished	Ra 0.4 µm	Aesthetic or sliding surfaces

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