Design Guidelines: CNC Milling

Our basic guidelines for CNC milling include important design considerations to help improve part manufacturability, enhance cosmetic appearance and reduce overall production time.



Maximum Dimensions (3-axis milling)

254mm x 178mm x 95mm
254mm x 356mm x 44mm*
559mm x 356mm x 32mm**
559mm x 356mm x 95mm***

Maximum Dimensions (5-axis milling)

66mm x 73mm x 99mm

Minimum Dimensions

SIZE 6.35mm x 6.35mm



Soft metals Ø0.5 mm, plastics Ø0.6 mm and hard metals Ø1.2 mm*

*Note: Generally in; soft metals Ø0.5 mm, plastics Ø0.6 mm and hard metals Ø1.2 mm, holes/slots can be machined.

For more detail, upload your CAD for DFM advice.

There is a relationship between width and maximum depth, so designers should consider bigger holes/slots, where possible

Typically, Protolabs can maintain a machining tolerance of +/- 0.1 mm. Parts may be as thin as 0.5 mm in regions as long as nominal part thickness is above 1 mm. Maximum depth that can be milled is 50 mm from either side of part. For specific milling dimensions by material, see maximum part extents for machining.

*These part sizes can only be milled from two sides, and in ABS natural, Acetal black, Aluminium 6082/ 2024/ 7075.

**These part sizes can only be milled from two sides, and in Aluminium 6082, 2024 and 7075.

***These part sizes can only be milled from two sides, and in Aluminium 6082.

5-Axis Milling Capabilities

We use 5-axis indexed milling—in addition 3-axis milling and turning—to machine parts. 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.


5-axis milling is available for metals only.


  • ABS 
  • Acetal
  • CPVC
  • HDPE 
  • LDPE
  • Nylon
  • PEEK
  • PEI
  • PET 
  • PMMA
  • Polycarbonate
  • Polypropylene 
  • PPSU
  • PS
  • PSU
  • PTFE
  • PVC 
  • Aluminium
  • Brass
  • Copper 
  • Stainless Steel
  • Steel Alloy
  • Steel Mild Low Carbon
  • Titanium


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. Soft metals like brass, copper, and aluminium 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.



As-machined, deburred, or deburred with a light bead blast

Threaded Holes

We currently support UNC and UNF threads from #2 up to 1/2 in., and metric threads from M2 to M12. Avoid modeling internal threads on your part design.




Sharp inside corners on a part will be radiused (rounded) as a natural result of the CNC machining process. Resulting radii will be identified before the part is milled.




Recommended text considerations for CNC milling:

• Recessed text should have a minimum stroke width of 0.5mm.

• The spacing between characters on raised text should be 0.5mm or greater.

• If design permits it, opt for raised text versus recessed.

team of applications engineers

Free DFM analysis within hours


Request More Information

Thank you
customer service representative