Milling

Milling removes material with rotating cutters to produce precise flat and contoured features on prismatic parts, supporting tight tolerances and complex 3D geometries.

Overview

Milling is a subtractive machining process that uses rotating cutting tools to remove material and create accurate flat surfaces, pockets, slots, and complex 3D contours. It excels at prismatic parts and multi-face features, especially when using 3-, 4-, or 5-axis CNC machines or gantry mills for large components.

Use milling when you need good dimensional accuracy, clean surface finishes, and the flexibility to iterate designs quickly from prototype through low-to-medium production volumes. It handles a wide range of metals and plastics, but part cost rises with deep cavities, tiny tools, and heavy material removal. Tradeoffs include longer cycle times on very large stock removal, limited ability to create sharp internal corners, and higher setup costs for complex fixturing or multi-side machining.

Common Materials

  • Aluminum 6061
  • Aluminum 7075
  • Steel 1018
  • Steel 4140
  • Stainless Steel 304
  • ABS plastic

Tolerances

±0.001"–±0.005"

Applications

  • Machined brackets and mounts
  • Valve bodies and manifolds
  • Equipment housings and panels
  • Mold bases and mold plates
  • Fixtures and inspection jigs
  • Heat sink plates and cold plates

When to Choose Milling

Choose milling for prismatic parts with flats, pockets, slots, and multi-face features that need accurate dimensions and reliable repeatability. It suits prototypes and low-to-medium volumes where flexibility and setup changes matter more than raw cycle time. It is especially effective for parts needing multiple features aligned across several faces or moderate 3D surfacing.

vs Turning

Choose milling instead of turning when the part is not primarily rotational, or when key features are flats, pockets, slots, or patterns on multiple faces. Milling is better for rectangular or irregular shapes, complex 3D surfaces, and parts that cannot be held efficiently as round stock in a chuck.

vs Drilling

Choose milling instead of drilling when you need more than simple round holes—such as pockets, slots, counterbores, profiles, or interpolated holes with tight positional tolerances. Milling can combine drilling operations with contouring in a single setup, improving feature alignment and reducing total setups.

vs Grinding

Choose milling instead of grinding for most stock removal and general feature creation where standard machining tolerances and finishes are acceptable. Milling gets you close to final size efficiently, leaving grinding only for critical surfaces that need ultra-tight tolerances or very fine surface finishes.

vs Electrical Discharge Machining (EDM)

Choose milling instead of EDM when the material is easy to cut, features are accessible with standard tools, and ultra-sharp internal corners or extreme hardness are not required. Milling usually offers lower cost and faster turnaround for general prismatic parts, reserving EDM for hard materials, deep narrow slots, or intricate internal geometries.

vs Broaching

Choose milling instead of broaching when you need flexibility in geometry, lower part volumes, or when you do not want to invest in dedicated broach tools. Milling is ideal for varied keyways, slots, and contours that change from design to design, whereas broaching only makes sense for high-volume, repeatable internal profiles.

Design Considerations

  • Model realistic corner radii so internal corners match standard end mill sizes; avoid specifying sharp internal corners
  • Limit pocket depth relative to tool diameter (ideally ≤3–5x) to avoid chatter, deflection, and excessive cycle time
  • Keep wall thicknesses robust where possible; thin walls drive special tooling, lighter cuts, and longer machining times
  • Consolidate setups by designing clear datum surfaces and clamping areas that are flat, accessible, and free of critical features
  • Specify tolerances no tighter than functionally required; over-tolerancing dramatically increases machining and inspection cost
  • Avoid unnecessary 3D surfacing on cosmetic areas; use planar faces and simple chamfers/fillets wherever possible to reduce programming and runtime