CNC Milling

Rapid CNC machining manufactures custom parts from more than 30 different engineering-grade plastic and metal materials for high-quality prototypes, custom jigs and fixtures, and functional end-use parts. We use both 3-axis milling from 6 orthogonal sides and 5-axis indexed milling, which can accommodate complex geometries like off-axis features and non-orthogonal holes.
1 to 200+ parts
Shipped in 1 to 3 days
Parts start at $65

Design Guidelines


  • Maximum part size (3-axis milling): 10 in. by 7 in. (254mm by 178mm)
  • Maximum part size (5-axis milling): 2.6 in. by 2.9 in. by 3.9 in. (66mm by 73mm by 99mm)
  • Minimum part size: 0.25 in. by 0.25 in. (6.4mm by 6.4mm)
  • Maximum part depth: ranges from 0.75 in. to 3.75 in. (19mm to 95mm). The maximum depth that can milled from either side of the part is 2 in. (51mm). Please see our materials selection guide for more information.

Larger sizes

With 3-axis milling, larger part sizes may be available in ABS, acetal, aluminum 6061 and 7075, and magnesium materials.
  • For these materials with depths up to 1.75 in. (44mm), maximum size increases to 10 in. by 14 in. (254mm by 356mm).
  • For these materials with depths up to 0.75 in. (19mm), maximum size increases to 22 in. by 14 in. (559mm by 356mm).
  • For parts in aluminum 6061, depths up to 1.25 in. (32mm) are possible with a maximum part size of 22 in. by 14 in. (559mm by 356mm).
Larger parts can be milled from top and bottom only—no side setups. Both standard and larger envelope sizes are nominal; parts that fit within these constraints occasionally cannot be manufactured due to fixturing or other considerations.

5-axis milling capability

Along with 3-axis milling, 5-axis indexed milling is used at Proto Labs. With 5-axis indexed milling (also referred to as 3+2 milling), two axes are stopped while the tool is engaged with the part. This allows for more complex geometries and non-orthogonal features like off-axis holes. Better finishes are also possible on non-orthogonal surfaces and because 5-axis milling increases machining efficiencies, more cost-efficient parts can be had.
Firstcut size limits


Our CNC machining process typically requires nominal part thickness to be larger than 0.040 in. (1mm). Parts may be as thin as 0.020 in. (0.5mm) in regions as long as the nominal part thickness stays above 0.040 in. (1mm). Features thinner than 0.020 in. (0.5mm) typically do not survive the machining process.


In general, tolerances of ±0.005 in. (0.13mm) are expected and achieved.


Sharp inside corners on a part will be radiused (rounded) as a natural result of the CNC milling process. Our automated quotes highlight areas where these radii will occur.

Text on parts

Recessed text should have a minimum stroke width of 0.020 in. (0.5mm). The spacing between characters on raised text should be 0.020 in. (0.5mm) or greater. If your design permits it, opt for raised text versus recessed.

Surface finishes

All machined plastic parts are left as-milled, which typically means they show visible tool marks. Some metal parts, on the other hand, allow more choice. Magnesium, like plastic, is always left as-milled. Soft metals like brass, copper and aluminum can be lightly bead blasted leaving a fine matte finish. Hard metals like steel and stainless steel can also be de-burred with a light bead blast which removes metal slivers and sharp or particularly rough areas.
Surface finishes
Firstcut plastic as-milled finish
Plastic as-milled
Firstcut metal as-milled finish
Metal as-milled
Firstcut bead-blasted finish
Firstcut de-burred finish
Firstcut plastic as-milled finish
Plastic as-milled
Firstcut metal as-milled finish
Metal as-milled
Firstcut bead-blasted finish
Firstcut de-burred finish

Threaded holes

We provide the ability to easily add threaded holes to machined parts. We currently support UNC and UNF threads from #2 up to 1/2 in., and metric threads from M2 to M12. Because of the lack of standards between CAD packages for specifying threads, our automated systems decide where to put threads by looking for holes that could be pilot holes that are oriented suitably. Please avoid modeling internal threads on your part design. More details.
Threaded holes
Firstcut threaded holes


We offer a range of plastic and metal materials that can be CNC machined. Please note that only steel, aluminum, copper and brass are available for 5-axis machining at this time. See full list of materials.
  • ABS
  • Acetal
  • CPVC
  • HDPE
  • LDPE
  • Nylon
  • PEEK
  • PEI
  • PET
  • PMMA
  • Polycarbonate
  • Polypropylene
  • PPE/PS
  • PPSU
  • PS
  • PSU
  • PTFE
  • PVC
  • UHMW
  • Aluminum
  • Brass
  • Copper
  • Magnesium
  • Stainless Steel
  • Steel Alloy
  • Steel Mild Low Carbon
  • Titanium