The Unique Nature of CNC Plastic Machining

The world of CNC manufacturing is inherently complicated. Customers and engineers demand difficult, intricate parts, and expect reasonable turnaround times at a competitive price. However, it’s not uncommon for things to go wrong, or for problems to be far more complicated than first imagined. No matter how you slice it, CNC manufacturing is a tough world that requires tough-minded people to get the job done. Things become ever more difficult when you add one simple word to that phrase: CNC Plastic Machining. 

Things become increasingly difficult when you add in additional variables, like the type of material being used. Not all materials can be treated the same. Some are harder, requiring tougher tooling, and some are softer, which can present issues with galling or debris buildup on cutting surfaces. And that’s only scratching the surface of the issues and considerations that need to be made with different materials.

Cutting plastic requires an entirely different understanding than cutting metal, given its different makeup and characteristics. But what exactly are the differences between the two?

The following is a list of five different challenges that you may encounter while trying to cut plastic.


Chipping and cracking are common problems with brittle plastics. The likelihood of chipping or cracking increases with thin cross-sections and sharp corners. It is, therefore, necessary to machine these parts slower. Choosing the right tool path and cutter can help to alleviate this issue. Plastic may crack under heat, so it is recommended to have proper cooling measures like coolant and fans to help as well.


Burrs are a common occurrence in most machining processes, but they are often more frequent when machining plastic materials because of their softness. While some burrs can be removed by machining extra passes, others need to be deburred later on by hand, which is usually the best method of catching any stragglers.


When machining plastic sheet stock, parts are prone to warping. A thin sheet of plastic or certain types of plastic resins are more likely to show this type of deformation. Modifying the tool paths can minimize the effects of stress that causes warping. Much like the issue of cracking, temperature control and feed speeds also play a role in how the material behaves.

Fixturing and Tooling Complications

Plastic materials/parts that are brittle or too soft can pose a challenge when holding. Overtightening the fixture can lead to damage or warping of the parts. Cutter wear is typically greater with plastics, sometimes drastically so. This requires careful selection of the cutter, as well as frequent monitoring. If you are machining plastics, uncoated tools produce a much smoother finish, but they are more susceptible to wear and tear.

Distorted Raw Material

Due to their general malleability, sheets of plastic are not always perfectly flat, and plastic rods are not always straight. Fixturing and bar feeding can be challenging as a result. Thus, it is important to qualify raw plastic materials before machining. A machinist can solve these issues by using techniques such as fly-cutting.

The nature of the plastic manufacturing industry is combatting the ever-present process of entropy. Things always go wrong, but it’s up to the experts in the industry to make it right. Half the battle is knowing what can go wrong, and then being prepared and equipped with the proper tools to solve the issue. Hopefully, this list leaves you feeling just a bit more prepared to solve the common issues involved with CNC plastic machining.