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Your Ultimate Guide to Plastic CNC Machining

Your Ultimate Guide to Plastic CNC Machining
The Silicon Review
19 December, 2019

CNC, or Computer Numerical Control, represents the automated control of machining tools with the use of a computer. CNC machining is essentially a manufacturing process in which you pre-program computer software to dictate how machinery will make parts. CNC machines can work with different materials, like plastic, metal, composite, ceramic, and wood.

Most people use this manufacturing process to make plastic parts. After all, plastic is a very cheap, durable, and lightweight material. Plastic CNC machining can create parts with complex shapes without missing a single detail. No matter the size of your desired parts, you can use this manufacturing process to create what you need.

How CNC Machining Works

Along with 3D printing, CNC machining is currently the only process that enables you to create a physical part from a computer design file. Nevertheless, these two processes are very different.

While 3D printing creates a part from a certain material through an additive process, CNC machining basically works by removing material from a solid block using different cutting tools to provide you with your desired shape.

Although both processes can provide you with equally good parts, CNC machining is without a doubt the superior option if you have to manufacture something in large quantities. It’s worth noting that once you program a machine properly, the output will be consistent every time. On top of that, it’s a known fact that machined parts have better mechanical properties than those that are printed.

The software used to control the machine is programmed with a specific CNC machine language known as G-Code, which is used to determine various features of the machines, including speed, feed rate, and coordination.

The Different Types of CNC Machines

Any machine that’s controlled by a set of commands from a controller can be referred to as a CNC machine. Factories typically use four different types of CNC machines to make plastic parts.

These include:

  • CNC Mills – These machines are usually used when you need to create a flat part. It works by holding the plastic material stationary while the spindle rotates with the tools along three axes to create the shape it was programmed to make.

    In some cases, the machine is programmed in a way to make the spindle stationary while the material moves into it.

  • CNC Lathes – When you need to make a plastic cylindrical part, you should use a CNC lathe. This allows you to create curved surfaces that you would never be able to make on a manual lathe.

    These machines work by spinning the material in the chunk of the lathe while a tool is moved in two axes to create your desired shape.

  • CNC Grinders – Typically used for creating surface finishes of high quality, CNC grinders work by moving a grinding wheel into the plastic. It’s worth noting that you should use these machines only for hardened plastic.
  • CNC Drills – Similar to CNC mills, the only difference between these two machines is that drills are designed to cut along one axis only. Namely, the drill moves down the Z-axis.

How is Plastic CNC Machining Different?

The most important thing that you should know is that there are no special machines used for manufacturing plastic parts. You can use the same machine to create both metal and plastic parts. With that being said, there are some things you should pay attention to when it comes to plastic CNC machining.

For instance, it won’t be that easy finding the right cutting tools for your needs, especially if you don’t have a lot of prior experience with CNC machines. One of the main reasons why you should pay close attention to the cutting tools you use is due to the varying composition of the plastic. It’s important to take the composition of the plastic into consideration since each type of this material will react to machining differently.

Keep in mind that some plastics are often hardened with carbide particles, which will enhance certain factors of the material, like thermal resistance. Although the milling and drilling tools used for metal and plastic are similar, there are some differences.

Namely, the tools used for machining metal have wider angles to make them more resistant. On the other hand, plastic cutting tools have sharper angles that would not otherwise work on metal.

In order to get the perfect product, there are a few things to consider when milling plastic:

  • First of all, the clamping should be free of tension to minimize distortion.
  • Secondly, the cutting tool should be very sharp.
  • Finally, you should use a coolant directly at the cutting tool to prevent a rupture. Make sure that the rotation speed of the cutting tool is low to prevent the temperature of the plastic from becoming too high.

The Different Types of Plastic Materials You Can Use

Belgian-born inventor named Leo Baekeland was the first person to create fully synthetic plastic. This was the first time a material was made that didn’t contain any molecules found in nature. Considering how plastic is widespread today, it’s safe to say this was one of the most revolutionary inventions of all time.

Today, you can use CNC machines to automate the process of manufacturing from different types of plastic.

Here are some of the most common plastic CNC materials today:

PVC: PVC is a plastic material used for various applications in most industries due to its cost-effectiveness, durability, and strength. Despite being such a strong material, PVC is very lightweight, which is why it is often used in construction.

Another thing worth mentioning is that this material is very safe. Keep in mind that PVC is more affordable than other CNC materials.

Nylon: Most people use nylon for CNC machining to make bearings, insulators, and products for injection molding. One of the main benefits of this material is that it’s incredibly easy to machine. Nylon is noted for its low-friction properties. Due to its composition, it’s often used for parts that could see a lot of wear.

It’s worth noting that this material is often used for making toys. In case you have a company that sells these products, you may be able to benefit from automated manufacturing. Nylon is prevalent in the automotive industry when it comes to certain parts, like radiator grills and door handles.

PEEK Plastic: PEEK stands for polyether ether ketone, a high-performance engineering plastic. It’s noted for its incredible resistance to harsh chemicals. On top of that, it has outstanding impact strength and dimensional stability. It’s very easy to machine PEEK plastic, which is why it’s among the top materials used in CNC machining.

PEEK plastic is often used in the automotive, aerospace, medical, and electrical industries due to its amazing properties. The only disadvantage of this material is its high price. Nevertheless, you should definitely consider using it in case you need high-performance and resistant plastic.

This type of plastic is known to outperform metals used in chemical and processing industries. In some industries, it’s currently replacing metals, like stainless steel and aluminum.

How to Set Up Plastic Blocks

In case you have some experience with metal CNC machining, you should be cautious when you start working with plastic. Keep in mind that plastic is not nearly as hard as metal.

With that being said, you should never clamp the plastic block with too much force. Otherwise, it may end up with a large mark on the surface.

The best way to ensure your blocks don’t have any marks on the surface is to use pads from a softer material between the part and the fixtures.

Making Prototypes with Plastic CNC Machining

Plastic CNC machining is an excellent way to make prototypes. After all, polymer materials, like plastic, are usually used for engineering validation and creation of prototypes. The reason why plastic is such a popular choice material is that it’s easy to machine it. You just need CNC plastic blocks to get your desired prototypes in a short period of time.

If you were to make a prototype using metal, you would need both molding and heating equipment. However, when it comes to making plastic parts, you just need a block of the material.

Why Should You Use CNC Machines?

Automating processes can help bring your company to the next level. If you’re currently dishing out a lot of money for manual labor in your manufacturing department, you should consider using CNC machines. Of course, considering the price of these machines, this is a decision that shouldn’t be taken lightly.

Before you make a purchase, it’s important to understand exactly why you should opt for CNC machining:

Scalability: If it has become a problem for you to complete orders by relying on manual labor, it’s definitely time to consider automating this process. Keep in mind that you’ll never be able to grow your business significantly if you don’t automate your manufacturing. This is a normal step every company has to take at a certain point.

Not only will plastic CNC machining allow you to fill orders more efficiently, but it’ll also enable you to focus on other designs. In other words, it’ll be easier for you to create different prototypes and make new products, which is also vital for the growth of your company.

Less Labor Needed: When you have a small business, manufacturing costs usually aren’t that high. However, as your company starts to grow, it soon becomes very expensive to hire labor to do manufacturing. Instead of paying several different employees to make your products, you can simply get several CNC machines and have one machinist watch over them.

This can save your business a lot of money in the long run. Not to mention that it will also allow you to easily expand your manufacturing when the time is right. Keep in mind that CNC machines can work long hours and even overnight to create as many plastic parts as you need. In fact, these machines can remain turned on for weeks at a time. They only need to be turned off when maintenance is required.

Almost every time you use plastic CNC machining to make a certain part, it’ll be flawless. The risk of human error is exponentially higher than a CNC machine error when it comes to manufacturing.

Aside from needing less labor, you won’t have to worry about things that are out of your control interfering with manufacturing. For instance, you won’t have to face the challenges of replacing a worker who called in sick on short notice to fulfill your orders. Thus, with automated manufacturing, there are simply fewer logistical issues you can encounter.

Quality: No matter how good your manufacturing staff is, a machine could do a better job of making products according to your specifications. Keep in mind that the computer systems that control CNC machines are extremely precise, so you’ll hardly ever encounter a problem with the end product.

On top of that, a CNC machine will provide you with an excellent plastic part every time, whereas the chance of human error or damage during handling is way too common in manufacturing. It’s worth noting that CNC software is so advanced that you don’t even have to produce a prototype.

Flexibility: One of the main advantages of CNC machines is their flexibility. In other words, you can easily reprogram it to make a completely different plastic product within just a few hours. On the other hand, teaching your employees how to manufacture a new product can take weeks.

In case you need to make a product that hasn’t been manufactured for a while, you can simply refer back to old designs. No matter what you need to make, you can easily shift between producing entirely different products using CNC machines.

Keep in mind that this will allow you to always keep up with customer demand.

Labor Safety: Whenever manufacturing work is being done, accidents are bound to happen. One of the main benefits of using CNC machines is that you’ll have fewer accidents in the workplace. The machinist operating them won’t have to go near the cutting tools, which will ensure his safety.


Plastic CNC machining is an excellent way to make physical parts from computer design files. You can use this method to automate your manufacturing, which will help boost the quality of your products, reduce accidents in the workplace, and save money.