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Introduction to CNC Machining Plastics

A variety of different types of plastic parts produced through CNC machining.

Image courtesy of FormLabs

This is one of CNCCookbook’s Material-Specific Machining Guides.

Definition and Overview of CNC Machining

CNC (Computer Numerical Control) machining is a sophisticated manufacturing process that utilizes computerized controls to automate the movement of machine tools. This technology has revolutionized the way various materials, including metals, wood, and plastics, are shaped into precise components. In the realm of plastic manufacturing, CNC machining represents a remarkable advancement in terms of accuracy, efficiency, and versatility.

Introduction to Plastics and their Properties

Plastics are synthetic materials characterized by their ability to be molded into various shapes while maintaining their structural integrity. They are derived from polymers, which are long chains of molecules formed through chemical reactions. The properties of plastics can vary widely depending on factors such as molecular structure, additives used during processing, and the manufacturing technique employed.

Plastics possess numerous advantageous properties that make them appealing for a wide range of applications. They can be lightweight yet durable, have excellent resistance to chemicals and corrosion, exhibit electrical insulation properties or conductivity when required.

Additionally, plastics can withstand high temperatures or remain flexible at extreme cold conditions based on their composition. These versatile characteristics enable engineers and designers to create products with intricate geometries that fulfill specific functional requirements.

Importance of CNC Machining in Plastic Manufacturing

The significance of CNC machining in plastic manufacturing cannot be overstated. This advanced technology enables precise shaping and cutting of plastic components with exceptional accuracy at a rapid pace. With CNC machining techniques such as milling, drilling, turning, and routing specifically tailored for plastics’ unique properties; manufacturers can achieve complex designs with tight tolerances.

Furthermore, CNC machining allows for high repeatability in production batches since the machines operate based on programmed instructions rather than manual intervention. This consistency is crucial in industries such as automotive or aerospace where strict quality control measures are mandated.

Moreover, CNC machining reduces the dependence on human labor, resulting in increased productivity, reduced errors, and improved overall efficiency. CNC machining has revolutionized the plastic manufacturing industry by offering precise control over the production process.

From design to execution, this technology provides engineers with unparalleled flexibility in creating intricate geometries using a wide range of plastics. The next sections will delve deeper into understanding the intricacies of the CNC machining process and shed light on its advantages when applied specifically to plastic materials.

Types of Plastics Suitable for CNC Machining

Thermoplastics vs Thermosetting Plastics

When discussing plastics suitable for CNC machining, it is important to distinguish between thermoplastics and thermosetting plastics. Thermoplastics are polymers that can be melted and re-molded multiple times without undergoing any significant chemical change. They have a high level of molecular mobility, allowing them to be easily shaped and machined.

On the other hand, thermosetting plastics are polymers that undergo a chemical reaction during their initial curing phase, irreversibly solidifying into their final form. Once cured, they cannot be re-melted or reshaped without undergoing decomposition.

9 Commonly Used Plastic Materials in CNC Machining

There is a wide range of plastic materials suitable for CNC machining, but some stand out as popular choices due to their unique properties and ease of machinability.

– Acrylonitrile Butadiene Styrene (ABS):

ABS is a popular engineering thermoplastic known for its high impact strength and resistance, high head resistance, and good machinability.  It is a good insulator, so it ideal for electrical applications, and it remains mechanically stable over time.

It is frequently used for rapid prototyping of electronics enclosures, keyboard caps, and automotive dashboard components.

It is highly susceptible to wear by certain greases, solvents, and alcohols, so be sure to check your coolant on it.  If it hasn’t been treated with heat stabilizers, ABS will burn easily, even to the point of burning after the flame has been removed.

– Polytetrafluorethylene (PTFE)

PTFE is commonly known as Teflon.  It’s a versatile high-performance polymer with many excellent properties.  It is chemical-, temperature-, light-, UV-, water-, weathering-, and fatigue-resistant.

Teflon has excellent anti-adhesion properties, and is most commonly found in coatings for non-stick kitchenware but may also be used for gaskets, semiconductor parts, and medical devices.

PTFE has the lowest friction coefficient of any solid material and is one of the top five most corrosion-resistant plastics.  Unfortunately, PTFE’s mechanical properties are generally inferior to other plastics at room temperature.  This can be improved by adding various fillers.  PTFE is also sensitive to creep and abrasion.

Polycarbonate (PC):

Polycarbonate is a versatile thermoplastic known for its exceptional clarity, high impact resistance, and excellent dimensional stability.

It can withstand high temperatures without melting or deforming, making it ideal for applications requiring transparency and toughness like safety goggles or medical devices.

– Polyvinyl Chloride (PVC):

PVC is a widely used engineering plastic.  It generally comes in either plasticized or unplasticized forms.  Unplasticized is used in rigid parts like pipes and fittings.  This is the form that sees the most CNC Machining.

Plasticized PVC is suitable for applications that require flexibility, such as cables or small tubes.  PVC uses fewer nonrenewable raw materials so it is one of the greenest plastic available.  It machines relatively easily.

PVC has excellent ultraviolet resistance, it insulates well, and it is resistant to moisture.  It is a popular choice for piping and construction materials and is used in the electrical, energy, and medical industries.

Acrylic (PMMA):

Acrylic, also known as polymethyl methacrylate (PMMA), is appreciated for its optical clarity and scratch resistance.

It can be easily machined into various shapes while retaining its transparency.  It is widely known for its shatter resistance and is highly resistant to most laboratory chemicals.  However, it will break down when used with chlorinated or aromatic hydrocarbons, ketones, or esthers.  Also, PMMA is not very resistant to heat, impact, wear, or abrasion.  Product teams should only consider PMMA for low-stress applications.

Acrylic finds extensive use in signage, lighting fixtures, display cases, and architectural applications due to its aesthetic appeal.

– Polyetheretherketone (PEEK):

POOK is a high-performance thermoplastic that is known for being resistant to chemicals, wear, creep, fatigue, liquids, and temperatures up to 260C (480F).  It’s also lightweight, able to endure harsh environmental conditions, and insoluble in all common solvents.  Even better, PEEK is recyclable and biocompatible.

Like nylon, PEEK often replaces metal parts in CNC Machining.

Despite all that, PEEK isn’t resistant to UV light and doesn’t hold up will in the presence of halogens or sodium.  It is also one of the more expensive CNC machining plastics, so product teams should reserve it for their most demanding applications.

– Polyacetal polyoxyethylene (POM)

POM is typically known by its tradename, Delrin.  It is one of the most machinable of all CNC plastics and is a pleasure to work with.  It’s ideal when a high-strength, high-stiffness plastic with excellent heat, wear, weather, chemical, and fuel resistance is needed.

Delrin 570 and 150 are the most common grades of POM used in CNC Machining because they have excellent dimensional stability and are ideal for creating precise parts with tight tolerances.  However, they have poor resistance to acids and they can be difficult to bond.

POM is commonly used to make seat belt components, electronic cigarettes, insulin pens, and water meters.

Polyethylene (PE, LDPE, HDPE, and UHMW):

Polyethylene comes in different variants such as high-density polyethylene (HDPE), low-density polyethylene (LDPE), and ulra-high molecular weight (UHMW). It exhibits excellent chemical resistance along with good electrical insulation properties.

PE is often used in industries such as packaging, automotive, and construction for components that require durability and resistance to impact or moisture. Polypropylene (PP): Polypropylene is a lightweight thermoplastic known for its high chemical resistance, low cost, and good mechanical properties.

It can be easily machined into complex shapes while maintaining its strength. PP is widely used in applications such as automotive parts, food packaging, and household appliances.

– Polypropylene (PP)

Polypropylene is a cost-effective CNC Machining Plastic that offers a unique combination of properties.

It is lightweight, highly chemical resistant in corrosive environments, and resistant to most organic solvents, degreasing agents, and electrolytes.

Compared to LDPE and HDPE, PP has a lower impact strength but makes up for it in tensile strength.  Similar to PTFE, PP is limited to 3-inch thick sheets, so part size is limited.

– Nylon 66 also known as Polyamide (PA):

Nylon is a strong and durable thermoplastic characterized by its high tensile strength and resistance to wear. It exhibits excellent mechanical properties even at elevated temperatures.

Nylon can be machined into precision parts like gears, bearings, and bushings due to its self-lubricating nature and ability to withstand repetitive stress. Understanding the distinctions between thermoplastics and thermosetting plastics is crucial in determining their suitability for CNC machining.

Polycarbonate, acrylic, polyethylene, polypropylene, and nylon are among the commonly used plastic materials with unique characteristics that make them highly suitable for CNC machining processes. By selecting the appropriate plastic material based on the specific requirements of an application or project, manufacturers can achieve precise results while taking advantage of each material’s distinct properties.

– Garolite G-10:

Garolite is a thermosetting composite made from fiberglass and phenolic epoxy resin.  Since it is thermosetting, it cannot be injection molded, so CNC Machining is the preferred manufacturing method for this material.

Garolite has a high strength-to-weight ratio and excellent corrosion and moisture resistance, making it ideal for marine applications.  It is also fire resistant and is a great choice for circuit board substrates given it is a great electrical insulator.

Step-by-Step Explanation of CNC Machining

Designing the CAD Model

In the CNC machining process, designing a precise and accurate CAD (Computer-Aided Design) model is crucial. The CAD model serves as the blueprint for the final product, dictating its dimensions, shapes, and features.

To create the CAD model, engineers use specialized software such as AutoCAD or SolidWorks. They meticulously design each component with specific measurements, taking into account factors like tolerances and material properties.

Selecting the Right Plastic Material

Choosing the appropriate plastic material for CNC machining is essential to ensure optimal results. Different plastics possess varying characteristics in terms of hardness, heat resistance, durability, and chemical resistance.

It is important to consider these factors while selecting a plastic material that suits your desired outcomes. For instance, polycarbonate is ideal for transparent applications due to its high clarity and impact resistance, while nylon exhibits excellent strength and toughness for load-bearing components.

For more on the properties of various plastics, see the section “9 Commonly Used Plastic Materials in CNC Machining” below.

Preparing the Machine and Tools

Once the CAD model has been designed and the plastic material selected, it’s time to prepare the CNC machine for operation. This involves mounting appropriate cutting tools onto their respective tool holders or spindles in accordance with the desired machining operations.

The tools are carefully selected based on factors like cutter geometry, flute count (for milling), or tip shape (for drilling). Additionally, special attention should be given to tool alignment within the machine’s tool changer to ensure precise positioning during machining operations.

Setting Up Parameters for Cutting Speed, Feed Rate, etc.

To achieve optimal results during CNC machining of plastics, it is crucial to establish suitable parameters that govern various aspects of cutting operations such as cutting speed (surface speed at which tools move across materials), feed rate (rate at which tools advance along axes), depth of cut, and spindle speed. These parameters are determined based on the specific plastic material being machined, its hardness, and the desired precision. For instance, softer plastics may require higher cutting speeds to prevent excessive heat generation, while harder plastics may demand lower speeds for improved surface finish.

Having correct feeds and speeds when machining plastics is essential to success.

Our G-Wizard Feeds and Speeds Calculator has a large database of plastics it can create feeds and speeds for:

Executing the Machining Process

Once all the necessary preparations have been completed, it is time to execute the CNC machining process. The programmed CAD model is loaded into the CNC machine’s computer system or controller. The machine then carries out precise movements along predetermined toolpaths, following instructions from the CAD model.

The cutting tools are engaged with the plastic material to remove excess material and shape it according to the desired design. Throughout this process, operators monitor and adjust parameters as needed to ensure optimal results in terms of dimensional accuracy and surface finish.

By following these steps diligently, CNC machining of plastics can yield exceptional results in terms of precision, complexity of designs achieved, and overall productivity. Understanding each step’s significance enables manufacturers to leverage this advanced manufacturing technique effectively while unlocking its full potential for a wide range of plastic applications.

Advantages of CNC Machining Plastics

Precision and Accuracy in Plastic Component Production

When it comes to manufacturing plastic components, precision and accuracy are crucial. CNC machining offers unparalleled precision, allowing for the creation of intricate and complex parts with tight tolerances.

The computer-controlled nature of the process ensures that every cut and movement is executed with meticulous accuracy, resulting in high-quality finished products. One of the key factors contributing to the precision of CNC machining is the use of advanced cutting tools, such as end mills and drills with multiple flutes.

These tools can achieve extremely fine cuts, enabling intricate details to be accurately reproduced on plastic surfaces. Additionally, CNC machines employ sophisticated measurement systems that constantly monitor and adjust for any variations during the machining process, ensuring consistent precision throughout production.

Versatility in Complex Geometries and Designs

CNC machining offers unparalleled versatility when it comes to handling complex geometries and designs in plastic components. Unlike other manufacturing processes like injection molding or 3D printing that may have limitations in terms of shape complexity, CNC machines can produce virtually any shape or form imaginable.

The ability to work with various axes – including X,Y,Z movements as well as rotational movements – allows for the creation of intricate features such as undercuts, pockets, chamfers, fillets, threads, and more. Whether it’s producing parts with intricate internal cavities or those requiring complex external profiles, CNC machining can handle them all with ease.

Furthermore, CNC machines offer compatibility with 3D computer-aided design (CAD) software which allows designers to create highly detailed models that can be directly translated into machine instructions. This seamless integration between design software and CNC machines empowers manufacturers to bring their most innovative ideas into reality without compromising on intricacy or design complexity.

Cost-effectiveness for Prototyping and Small Batch Production

CNC machining is highly cost-effective, particularly for prototyping and small batch production of plastic components. Unlike traditional manufacturing methods that require expensive tooling or molds, CNC machines can start the production process with minimal setup costs. This makes it an ideal choice for companies looking to test and refine their designs before committing to large-scale production.

Moreover, CNC machines offer flexibility in terms of material usage. They can effectively utilize standard-sized plastic stock materials, minimizing waste and reducing costs associated with material procurement.

Additionally, thanks to the precise nature of CNC machining, the need for post-processing operations is greatly reduced or eliminated altogether, further minimizing costs in terms of labor and time. Furthermore, CNC machines are capable of producing consistently high-quality results across multiple iterations.

This eliminates the need for costly reworks due to errors or flaws commonly found in manual manufacturing processes. By optimizing production efficiency and reducing wastage, CNC machining provides a cost-effective solution that meets the demands of both prototyping and small batch production.

Milling Techniques for Plastics with Low Melting Points

Unlocking the Potential of Polycarbonate, Acrylic, Polyethylene, etc.

When it comes to machining plastics with low melting points such as polycarbonate, acrylic, and polyethylene, employing appropriate milling techniques is crucial to ensure optimal results. These materials possess unique properties that require careful consideration during the machining process. One essential technique is the selection of suitable cutting tools and their proper configuration.

Using sharp and well-maintained end mills with a high number of flutes can help reduce heat build-up and prevent melting or warping of the plastic. Additionally, it is advisable to employ techniques like climb milling rather than conventional milling to minimize chip load and ensure smoother cutting.

Moreover, controlling the cutting speed and feed rate plays a pivotal role in achieving desired outcomes. Lowering the cutting speed while increasing the feed rate helps manage heat generation during milling.

Cooling techniques such as employing coolant or compressed air can further enhance performance by dissipating excess heat produced during the process. By implementing these strategies alongside precise toolpath planning, CNC machinists can achieve exceptional surface finishes while mitigating potential issues associated with low melting point plastics.

Drilling Techniques for Harder Plastics

Mastering Precision in Machining Polypropylene, Nylon, etc.

When faced with harder plastics like polypropylene and nylon that require drilling operations using CNC machinery, specific considerations come into play to ensure accurate results without compromising material integrity. Firstly, selecting appropriate drill bits specifically designed for plastic machining is crucial for achieving clean holes without unwanted chipping or cracking along the edges. Carbide drill bits are typically ideal due to their exceptional hardness and ability to withstand high temperatures generated during drilling.

Furthermore, carefully controlling spindle speed based on material type ensures effective chip evacuation and prevents excessive friction-induced heat that may cause undesirable outcomes. Low spindle speeds reduce the likelihood of melting or deforming the plastic, while high spindle speeds can lead to more efficient chip removal.

Additionally, utilizing peck drilling techniques where the drill bit is retracted periodically during the drilling process helps in evacuating chips efficiently and reducing heat build-up. By employing these drilling techniques alongside appropriate cutting fluids, machinists can achieve precise and clean holes in harder plastics.

Turning Techniques for High-Density Plastics

Tapping into the Potential of Machining High-Density Plastic Materials

Machining high-density plastics such as HDPE (high-density polyethylene) or POM (polyoxymethylene) through turning operations requires careful attention to detail to ensure optimal results. These materials offer excellent stiffness and robustness, but they also pose unique challenges due to their density and tendency to generate heat during machining. To overcome these challenges, several key techniques should be considered.

Firstly, selecting appropriate cutting tools with sharp edges and a suitable rake angle is vital for achieving smooth cuts without excessive material deformation or heat generation. Using carbide inserts designed for high-speed machining can significantly enhance performance and prolong tool life.

Additionally, ensuring proper tool geometry minimizes vibrations that could lead to poor surface finishes or premature tool wear. Controlling cutting parameters like cutting speed, feed rate, and depth of cut plays a crucial role in optimizing turning operations for high-density plastics.

Lowering cutting speeds while increasing feed rates promotes efficient chip evacuation while minimizing friction-induced heat accumulation. Similarly, using smaller depths of cut distributes cutting forces evenly and helps prevent excessive heat generation.

By employing tailored milling techniques for low melting point plastics like polycarbonate and acrylic, optimizing drilling techniques for harder plastics such as polypropylene and nylon, and implementing turning techniques suitable for high-density plastics like HDPE or POM, CNC machinists can unlock the full potential of plastic materials in their machining endeavors. Detailed knowledge of material properties, tool selection, and cutting parameters empowers machinists to deliver exceptional results while ensuring the integrity and quality of the machined components.

Tips for Successful CNC Machining of Plastics

Choosing the Right Tooling and Cutting Parameters

Selecting the appropriate tooling and optimizing cutting parameters is crucial for achieving high-quality results in the CNC machining of plastics. Regarding tool selection, consider using tools with sharp edges, as they provide cleaner cuts and minimize the chances of chipping or melting the plastic material.

Additionally, carbide or diamond-coated tools are recommended for their superior heat resistance. Regarding cutting parameters, pay attention to the spindle speed and feed rate.

For softer plastics like polycarbonate or acrylic, higher spindle speeds combined with lower feed rates can prevent overheating and ensure smooth cutting. On the other hand, harder plastics such as polypropylene or nylon require lower spindle speeds to avoid excessive heat generation.

Securing Proper Fixturing and Clamping Techniques

To prevent unwanted vibrations or movement during machining, securing proper fixturing is essential. The use of dedicated fixtures designed specifically for plastic workpieces helps in achieving stability and accuracy throughout the machining process. Consider utilizing vacuum tables or custom clamping systems that provide sufficient support without causing deformation or damage to delicate plastic components.

Moreover, when clamping plastic materials, it is vital to use appropriate pressure levels to avoid distortion or warping. Applying excessive force can lead to undesirable deformations in softer plastics while insufficient pressure might result in poor rigidity during machining intricate designs.

Implementing Efficient Chip Control Methods

Efficient chip control plays a significant role in CNC machining of plastics as it contributes to maintaining a clean work environment while enhancing overall productivity. To achieve optimal chip control, consider employing methods such as air blast systems or compressed air cooling during the machining process. These techniques help remove chips effectively while keeping temperatures under control.

Furthermore, utilizing suitable coolants specifically designed for plastic machining can assist in achieving excellent chip evacuation and preventing excessive heat buildup. These coolants are formulated to be non-reactive with plastics, ensuring the integrity of the material while facilitating smoother chip removal.

Test Your Coolant on the Material

Some coolants can cause crazing or other damage to certain plastics.  Always test your coolant on the plastic before machining.

More Material-Specific Machining Guides

Graphite Machining


Polycarbonate and ABS are commonly CNC machined plastics.  ABS is one of the most cost-effective and simplest materials to CNC machine.

Polyoxymethylene (POM or Acetal), which is also called Delrin, is a very easy to machine plastic.


CNC machining of plastics offers endless possibilities for creating intricate components with exceptional precision and accuracy. By following these tips for successful CNC machining, you can ensure high-quality results while minimizing issues such as melting, chipping, or warping.

Remember to choose the right tooling and cutting parameters, secure proper fixturing techniques, and implement efficient chip control methods. Embracing the advancements in CNC machining technology has made plastic manufacturing more accessible and efficient than ever before.

With meticulous attention to detail and a well-thought-out approach, you can harness the full potential of CNC machining in producing top-notch plastic components. So go ahead, explore the world of CNC machining plastics with confidence and take your projects to new heights!



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Recently updated on June 25th, 2024 at 04:23 pm