Machining (CNC) of plastic parts


Machining is frequently regarded as old technology or disregarded, as it is a subtractive not additive process, however it remains the benchmark by which most processes should be assessed. The issues that favour the RP processes are frequently cost and speed of response, those that favour machining would be material choice, accuracy and repeatability.

However, as Smartprotoype sources globally, we are able to deliver the benefits of machining at a competitive price point and in leadtimes of typically 10 days or less. (elapsed not working!)

The material options include ABS, PC, POM, PP, PMMA, PBT, PTFE, and Nylon giving a wide range of properties that whilst not having the structure of an injection moulded part, get very close in other properties.

Data format for machining is preferably STEP or IGES, STL is sufficient for quotation but not viable for completing the order.

Process Features


Minimum Feature Size

This is a geometry function as with machining it is also related to cutter reach/feature location. Preferably the smallest cutters used would be 1 mm, leaving a 0.5mm internal radius. However 0.2 mm cutters can be used if required.

Layer Thickness

Not applicable, machining is a continuous 3 axis process.

Bed Sizes

Bed sizes up to 800 x 600 mm are readily available with access to larger machines as required.

Post Processing

Most machined parts are manually dressed smooth and can be left natural, primed or painted as required.


Most machining work undertaken is 3 axis milling or turning as applicable. In some instances it is necessary to combine machining with fabrication where the part size is large, stock sizes are insufficient or complexity/reach prohibit access. In these instances all parts are assembled and dressed such that any indication of fabrication is removed.

Whilst parts may be supplied in a natural state, it is more common to supply parts dressed and primed ready for a final topcoat, or fully finished with texture/gloss finish as applicable.

Clear Parts using Machining

Clear plastic parts can be machined. and do the high polsih same as injection part.

Metal Parts using Machining

The same limitations apply to machining metal as apply to machining plastic, that acknowledged this usually represents the quickest way to achieve a metal prototype.

Whilst a range of materials is supplied the vast majority of this work is undertaken in aluminium using 3 axis machines. However, if the complexity or application demands it, full 5 axis capability is available in materials including Titanium and Magnesium.

With the sophistication of today’s machine tools and if the quantities are low enough, where a casting is going to require anymore than minimal post machining, then machining from solid should be considered. Not only is this possibly faster, but also bypasses many of the issues that can occur with casting, such as porosity.

Global sourcing delivers competitive solutions to 3 axis as well as 5 continuous axis work, facilitating a viable alternative to casting, where the geometry permits.

For more information, please contact:

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