Reviewed and updated September 12, 2026
In briefCNC machining uses programmed numerical instructions to control machine-tool movement. Material is removed from stock with cutting tools to create features defined by a CAD model and technical drawing.
From CAD to inspected part
- Design and requirements: a 3D model defines nominal geometry; the drawing defines tolerances, datums, threads, finishes and acceptance criteria.
- Process planning: the manufacturer chooses stock, workholding, machine, tools, setups and inspection method.
- CAM programming: toolpaths are generated and converted into instructions the controller can execute.
- Setup and machining: stock is located, tools are measured and material is removed in roughing and finishing operations.
- Verification: features are measured against the drawing; finishing, cleaning and documentation follow as required.
Milling, turning and combined work
In milling, a rotating cutter removes material while the workpiece is held. In turning, the workpiece rotates against a cutting tool. A part may need both: a primarily cylindrical body can be turned first, then cross-holes or flats can be milled.
| Geometry clue | Likely starting process | Typical examples |
|---|---|---|
| Prismatic, pocketed or planar | CNC milling | Housings, brackets, plates, manifolds |
| Rotational around a centerline | CNC turning | Shafts, sleeves, pins, threaded bodies |
| Rotational with off-axis features | Turn-mill or multiple setups | Valve bodies, connectors, custom fasteners |
What controls accuracy?
Accuracy is not a single machine specification. It depends on material behavior, tool condition, tool reach, setup rigidity, thermal stability, feature accessibility and the measurement strategy. This is why a responsible quotation reviews tolerances feature by feature.
What usually drives cost?
- Number of setups and orientations.
- Deep pockets, small internal radii and long-reach tools.
- Thin walls or features that can deflect.
- Broad use of tight tolerances or fine surface roughness.
- Special workholding, inspection, finishing and documentation.
What to send in an RFQ
- STEP/STP model and matching revision-controlled PDF drawing.
- Material grade, quantity now and expected repeat quantity.
- Critical fits, datums, threads and surface roughness.
- Finish, color, masking and cosmetic acceptance zones.
- Inspection records, certificates, packaging and delivery destination.
Sources and further reading
This article is an original engineering summary. Sources explain general principles; they do not replace project-specific process validation.