Design Guidelines: CNC Turning

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


Maximum Dimensions

Diameter 75mm



Minimum Dimensions

Diameter 4mm


Wall Thickness




Hole Diameter

Soft metals Ø0.5 mm and hard metals Ø1.2 mm*

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.

Small features may be allowed, but the diameter in any region should not be less than 0.76mm. Sharp conical points are allowed; angles should be greater than 30 degrees. Walls thinner than 0.5mm typically do not survive the machining process. For specific turning dimensions by material, see maximum part extents for machining.

Typically, Protolabs can maintain a machining tolerance of +/- 0.1mm.

Live Tooling Capabilities

Our lathe machines contain live tools that allow additional milled features to be added to turned parts including flats, slots, and grooves. We can also add on-axis, axial, and radial holes to turned parts, but only support holes that are either parallel or perpendicular to the axis of revolution, and we cannot accommodate holes at odd angles.


  • Aluminium
  • Brass
  • Mild Steel
  • Stainless Steel
  • Titanium


Get a realistic snapshot of the surface finishes that are possible on machined plastic and metal parts.

Surface Finishes


Parts that are turned typically have a very smooth surface finish. The as-machined surface finish of the cylindrical areas will typically be much smoother using the lathe than the mill, so consider this when selecting the machining method for those parts that qualify for either. Areas cut with live tooling, such as flats and slots, may have visible tools marks. If desired, the metal parts can be lightly bead blasted leaving a fine matte finish. Hard metals like steel and stainless steel can also have edges broken (deburred) with a light bead blast to remove metal slivers, and sharp or rough areas.




ALUMINIUM Edges broken with visible toolmarks, edges broken with light bead blast, or sharp edges with visible toolmarks
ALL OTHER METALS Edges broken with visible toolmarks or edges broken with light bead blast

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 before the part is milled. Turned outside corners will typically include a 0.13 mm chamfer.



Holes and Grooves

We can add on-axis, axial, and radial holes to turned parts, and we support holes that are either parallel or perpendicular to the axis of revolution. Holes at odd angles are not supported at this time.

Text on Parts

Text is not supported on turned parts at this time.

Minimum hole size:

  • On-axis and axial: 1mm
  • Radial: 2mm


  • Minimum OD groove width: 1.2mm
  • Maximum OD groove depth: 24.1mm—varies with groove width
  • ID grooves are not supported at this time
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