What is CNC Machining?

CNC machining is a subtractive manufacturing process. A machine starts with a solid block of material, usually metal or engineering plastic, and cuts material away until only your part remains. CNC stands for computer numerical control: the cutting tools are guided by a program generated automatically from your CAD file, not by a human operator turning handwheels.

How it works

When you upload a STEP file to OpusFab, the geometry is read and translated into a toolpath: a sequence of cuts a machine will follow. During production, rotating cutting tools remove material from the workpiece in controlled passes. Because the machine follows the same program every time, CNC machining is highly repeatable from part to part.

Mills and lathes

CNC machining covers two main machine types, and OpusFab lists them as separate processes:

• Milling (CNC Machining): the cutting tool spins and moves across a stationary or moving workpiece. Mills are best for prismatic parts: blocks, brackets, plates, housings, and anything with flat faces, pockets, slots, and drilled holes.
• Turning (CNC Turning): the workpiece spins in a lathe while a cutting tool shapes the outside or inside. Turning is best for round parts: shafts, pins, bushings, nozzles, and any geometry that is symmetrical around a central axis.

See CNC milling vs. turning for a detailed comparison.

Materials and tolerances

Because the part is cut from solid stock, its strength, density, and thermal behavior match the raw material exactly. This is a key difference from 3D printing, where layer lines can create directional weaknesses. Common CNC materials on the platform include 6061-T6 and 7075-T6 aluminum, plus stainless steels and engineering plastics. Check the material dropdown in the quote editor for the current live list.

CNC machining holds tight tolerances. On OpusFab, the standard tolerance shown at checkout for CNC parts is ±0.05mm. If your drawing requires tighter control on specific features, request a custom quote.

Surface finish

A machined part straight off the machine shows fine tool marks. The default finish is “Raw (As-Machined)”. You can add post-processing in the quote editor: bead blasting for a uniform matte look, anodizing for corrosion resistance and color, or powder coating for a durable colored surface. See Surface finishes overview.

When CNC is the right call

Choose CNC machining when:

• The part must perform like the final product under real mechanical load, heat, or chemical exposure.
• You need the same material as production, since substituting a weaker printed material can hide problems.
• You need tight tolerances for fit checks against other machined or molded components.
• You are in a later validation stage where the prototype should represent the production part closely.

CNC is usually not the best choice for very early concept models, where speed matters more than accuracy, or for geometries a cutting tool cannot reach, such as fully enclosed internal cavities. In those cases, look at SLA, SLS, or metal 3D printing. For a side-by-side decision, see Choosing a process.

DFM feedback on upload

OpusFab runs automatic DFM (design for manufacturability) analysis when you upload a part. Parts with potential machining problems, such as internal radii below the current 0.5mm warn threshold, get a “DFM Warning” pill in the quote table so you can fix the geometry before ordering. See DFM overview for what the checks cover.