Precision CNC Machining for Polymers: Advanced Techniques & Tips

CNC machining is a highly versatile manufacturing process. In addition to being able to work with rigid materials such as metals and wood, it also works very well with polymers. CNC machining of plastics is, in many ways, like CNC machining of all other materials. However, there is a number of key differences. These include the cutting tool, the speed and feed, the cutting fluid (mostly air), and the surface finish of the manufactured part.

Polymer CNC Machining or 3D Printing?

Many customers consider 3D printing as an effective alternative to CNC machining of polymers. There are certain factors that you need to be aware of when deciding between these two manufacturing methods for a particular project.

• Build size: CNC machining has a much larger build size than 3D printing. Our partner network includes manufacturers with up to 1.625.6 x 812 x 965.2 mm build size capacity for CNC machining, compared to 600 x 900 x 900 mm for 3D printing (FDM). For manufacturing large parts from plastic, CNC machining is better.
• Mechanical properties: Most 3D printing processes build parts layer by layer. As a result of this, the mechanical properties of manufactured parts are compromised. In many applications, this doesn’t constitute a problem. However, certain applications require plastic parts to have excellent mechanical properties. CNC machining doesn’t affect the mechanical properties of machined parts, and so the process is ideal for manufacturing plastic parts for applications that require good mechanical properties.
• Dimensional accuracy: CNC machining offers better dimensional accuracy (up to ±0.025 mm). It provides tight tolerances and is great for features such as holes, overhangs, bridges, and other hard to print features.
• Surface quality: as-machined surface roughness for the polymer CNC parts has a standard 3.2 μm, while 3D printing technologies such as FDM, SLS, HP MJF usually give lower roughness.
• Number of parts. Because of its repeatability, speed, and dimensional accuracy, CNC machining is a better option than 3D printing for large numbers of identical parts (>10). For prototyping, however, and very complex parts 3D printing could be a better solution.
• Price: 3D printing is cheaper for prototyping and for small numbers of parts. However, as a rule for more than 10 identical parts CNC machining would be a cheaper option.

Check out our manufacturing technology selection guide, which covers over 10 various factors.

Materials

The following are some polymers that can be effectively machined and are available for instant quotation on our platform.

• ABS
• Acrylic 
• Acetal / Delrin / POM
• Nylon / Polycaprolactam
• PEEK / Polyether ether ketone
• PTFE / Teflon
• PC / Polycarbonate
• UHMW PE / Ultra-high-molecular-weight polyethylene

Check out our overview of available CNC machining materials for more information on the above-listed materials.

Post-processing

CNC machining can produce parts that are suitable for use as-machined. This process produces a standard surface roughness of 3.2 μm. This can be fine as 0.4 μm. However, it may be necessary to carry out post-processing for various reasons. These include improving surface finish and improving aesthetics. The following are some post-processing operations that may be carried out on CNC machined plastic parts.

• Bead blasting: After machining, some loose plastic threads may remain on the body of a part. Bead blasting is used to remove these threads and produce a smooth surface finish.
• Dyeing: Dyeing is a popular operation carried out to change the colour of a part. There are very many colours available but note that some materials have more colour options than others. Please refer to our material guide for more information.
• Lacquering: Lacquering is used to achieve a glossy finish for machined parts. It also improved certain physical properties such as resistance to wear.

Conclusion

At Xometry Europe, we offer CNC machining for plastic parts. Through our network with over 2.000 manufacturers, we ensure quality, ease, and speed. Head over to our Instant Quoting Engine to upload your models,select material and finishing preferences, to receive a quote in seconds.