Key Points Precision CNC (computer numerical control) machining delivers standard tolerances of ±0.25 mm (±0.010") in most shop environments, with tighter tolerances available at measurable cost and lead time premiums Multi-axis capability, particularly 5-axis, unlocks complex geometries in single setups, but not every part needs it, and specifying it unnecessarily adds cost Tool geometry is the fundamental constraint: cylindrical cutters cannot produce sharp internal corners, and every design that ignores this will be modified during production Surface finish, material selection, and volume suitability all interact in ways that affect both what's achievable and what it costs The most capable CNC shops are vertically integrated, moving your part from machined housing through finishing, gasket dispensing, and assembly without changing hands Precision CNC (computer numerical control) machining is the default process for tight-tolerance metal parts across aerospace, defense, and medical device applications. Engineers know the name. Fewer understand what separates a well-executed CNC program from one that produces scrap, or what a shop's equipment configuration means for their part. This article covers the technology in enough depth to inform real decisions: what multi-axis machines can and can't do, how surface finish is specified and achieved, which materials machine cleanly, and what volume range CNC genuinely serves well. For a broader look at where CNC fits within precision manufacturing processes, tolerances, and industries , that pillar resource covers the full landscape.