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)

10 in. x 7 in. x 3.75 in.
10 in. x 14 in. x 1.75 in.*
22 in. x 14 in. x 0.75 in.*
22 in. x 14 in. x 1.25 in.**
254mm x 177.8mm x 95.25mm
254mm x 356mm x 44mm*
559mm x 356mm x 19mm*
559mm x 356mm x 32mm**

Maximum Dimensions (5-axis milling)

2.6 in. x 2.9 in. x 3.9 in.
66mm x 73mm x 99mm

Minimum Dimensions

SIZE 0.25 in. x 0.25 in.

0.040 in.

SIZE 6.35mm x 6.35mm


Typically, Proto Labs can maintain a machining tolerance of +/- 0.005 in. (0.127mm). Parts may be as thin as 0.020 in. (0.508mm) in regions as long as nominal part thickness is above 0.040 in. (1.016mm). Maximum depth that can be milled is 2 in. (50.8mm) from either side of part.

*ABS, acetal, aluminum 6061 and 7075, and magnesium materials only

**Aluminum 6061 only

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.

milling off-axis features and holes


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


milling a block of plastic

Surface Finishes

Typically, we break (debur) the edges on all machined parts. All machined plastic parts are left as-machined, which may leave visible tool marks. Some metal parts, on the other hand, allow more choice. Parts left with sharp edges should be handled with care.


Edges broken with visible toolmarks
Edges broken with visible toolmarks
Edges broken with visible toolmarks, edges broken with light bead blast, or sharp edges with visible toolmarks
Edges broken with visible toolmarks or edges broken with light bead blast
machined metal gear

Threaded Holes

We currently support UNC and UNF threads from #2 up to 0.5 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 on your quote.




Recommended text considerations for CNC milling:

  • Recessed text should have a minimum stroke width of 0.020 in. (0.508mm).
  • The spacing between characters on raised text should be 0.020 in. (0.508mm) or greater.
  • If design permits it, opt for raised text versus recessed.
machining text into a part

team of applications engineers

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Thanks for your interest in Proto Labs. Please let us know how we can provide more information on our services. Once we receive your comments, an applications engineer from our team will follow-up as soon as possible.

If you have a 3D CAD model of your part ready, upload it online now to receive an interactive quote with free design for manufacturability feedback within hours.

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