Milling

Milling removes material with rotating cutters to create flat faces, pockets, slots, and contours on prismatic parts with repeatable accuracy and flexible setups.

Overview

Milling is a machining process that uses a rotating cutting tool to remove material while the workpiece is held in a fixture. It’s the go-to method for prismatic geometry: planar faces, pockets, slots, profiles, bosses, and 3D contours. Common variants range from manual mills to 3-, 4-, and 5-axis CNC and gantry milling for large parts.

Choose milling for prototypes through medium volumes when you need tight feature control, good surface finish, and fast design iteration without tooling investment. Tradeoffs: internal corners require radii, deep pockets drive cycle time and chatter risk, and multi-side features may require additional setups unless using 4/5-axis. Cost is driven by material removal rate, tool reach, fixturing complexity, and inspection requirements.

Common Materials

  • Aluminum 6061
  • Aluminum 7075
  • Stainless 304
  • Stainless 316
  • Steel 4140
  • Titanium Ti-6Al-4V

Tolerances

±0.001" to ±0.005"

Applications

  • Machined housings and enclosures
  • Mounting plates and brackets
  • Precision fixture plates
  • Valve bodies and manifolds
  • Mold and die inserts
  • Pump and compressor components

When to Choose Milling

Pick milling when the part is primarily prismatic and needs controlled datums, flatness, and accurate pockets/slots. It fits best for prototypes and low-to-medium production where you want design flexibility and predictable lead times. It’s also a strong choice when multiple features must reference the same setup to control true position.

vs Turning

Choose milling when the part isn’t rotationally symmetric and you need pockets, flats, keyways, or complex external profiles. Milling also makes it easier to control relationships between multiple planar datums and hole patterns on different faces.

vs Drilling

Choose milling when you need more than simple holes: interpolated bores, counterbores with tight location, pockets, slots, and edge profiles in the same setup. Milling also supports helical interpolation for larger diameters or better positional control relative to milled datums.

vs Grinding

Choose milling when you need material removal and geometric features beyond precision finishing, or when tolerances and surface finish don’t justify grinding. Milling is typically faster and cheaper for bulk stock removal and complex shapes, with grinding reserved for ultra-tight size/finish.

vs Electrical Discharge Machining (EDM)

Choose milling for conductive materials when features are accessible with a cutting tool and you want faster throughput and lower per-part cost. Milling is better for open pockets, profiles, and 3D contours where EDM would be slow or require specialized electrodes/wire paths.

vs Broaching

Choose milling when quantities don’t justify dedicated broach tooling or when the feature may change during iteration. Milling can produce keyways and internal profiles in flexible ways, while broaching excels at high-volume repeatability once the design is locked.

Design Considerations

  • Avoid deep, narrow pockets; target pocket depth-to-width ratios that allow short, stiff tools
  • Add internal corner radii that match standard end mills; don’t model sharp inside corners unless required
  • Minimize setups by designing consistent datums and grouping critical features on accessible faces
  • Specify tolerances only where function demands; tight true position and flatness drive cost and inspection time
  • Provide clear material, finish, and critical-to-function notes; ambiguous callouts slow quoting and invite assumptions
  • Design for fixturing: include flat clamping surfaces and avoid thin walls that can distort under cutting forces