CNC (Computer Numerical Control) machining is a high-precision, efficient process for producing high-quality parts from diverse materials like ceramics, wood, and composites. If you need a plastic part and decide to have it CNC machined, the first step is to choose the right type of plastic. However, with so many machinable options available, how do you pick the right one? Keep reading— this article will guide you to the answers.
Common Plastic Materials Used in CNC Machining
Not all plastics are suitable for machining. A plastic’s machinability depends on key mechanical properties such as impact strength, wear resistance, and dimensional stability. These properties can also vary based on the material’s treatment—for instance, many high-temperature thermoplastics like PEEK and PPS undergo annealing before machining to reduce internal stress and improve stability.
Most thermoplastic materials can yield good results through CNC machining. Next, we will focus on the most commonly used plastics in CNC machining. For a broader selection of plastics, check out Chiggo’s Plastic CNC Machining Services for additional details.
ABS (Acrylonitrile Butadiene Styrene)
ABS is a versatile, general-purpose plastic offering excellent balance of toughness, impact resistance, and machinability at a low price. It is easy to process through injection molding, CNC machining, or 3D printing and has a relatively wide forming temperature range. It can also be easily finished with painting, coating, or plating.
However, ABS does not have good abrasion resistance and offers limited chemical resistance to strong acids, alkalis, and solvents. Prolonged exposure to UV light or harsh outdoor conditions can cause aging, discoloration, or cracking. Its strength and dimensional stability may also degrade in high-temperature environments.
Common Applications: Pre-injection molding prototypes, household appliances, electronic enclosures, automotive dashboards, and Lego bricks.
POM / Delrin/ Acetal (Polyoxymethylene)
Delrin is the DuPont trade name for homopolymer acetal. It has high tensile strength and stiffness, maintaining shape and strength under long-term or repetitive loads. With excellent dimensional stability and machinability, Acetal/POM is a top choice for CNC-machined plastic parts requiring precision and tight tolerances. Additionally, POM is highly resistant to various chemicals, including oils, fuels, weak acids, and bases. Its smooth surface and low friction coefficient make it particularly suitable for parts that require sliding or rolling applications.
POM can operate between -40℃ and 120℃ but may degrade or decompose at higher temperatures. Its UV resistance is poor, and as a flammable material, fire safety precautions are necessary during use.
Common Applications: Typically used in mechanical transmission parts, such as gears, bearings, pulleys, and cams. It is also widely used in automotive, consumer electronics, and medical devices.
Acrylic/PMMA (Polymethyl Methacrylate)
Acrylic, or PMMA, is a transparent thermoplastic with excellent optical properties. With a light transmission rate of up to 92%, it is even more transparent than glass and lighter in weight. These make it a lightweight alternative to glass or for light pipes. It also has good weather resistance and UV stability, performing well in outdoor environments.
Compared to engineering plastics like PC, PMMA has lower impact strength and is more prone to cracking or shattering. The surface is relatively soft and can scratch easily. Any machined surfaces on a piece of acrylic will lose their transparency and take on a frosted, translucent appearance. If transparency is needed on a machined surface, it can be polished as an additional post-processing step.
Common Applications: Light covers, display stands, optical lenses, decorative panels, screen protectors, and medical shields.
Nylon/PA (Polyamides)
Nylon is available in various forms, with Nylon 6/6 and glass-filled nylon being the most commonly used at Chiggo. Both are great materials for CNC machining and retain key benefits of standard nylon (e.g., Nylon 6), including high strength, toughness, low friction, exceptional wear resistance, and good chemical resistance.
Nylon 6/6 has a more ordered molecular structure and higher crystallinity compared to Nylon 6. This results in greater strength, rigidity, and a higher heat deflection temperature. While its moisture absorption is slightly lower than Nylon 6, it can still impact dimensional stability in humid environments.
Glass-filled nylon incorporates glass fibers, significantly enhancing strength and rigidity to handle high-load applications. It also has reduced thermal expansion, better dimensional stability, and superior heat resistance for demanding high-temperature environments. However, it is more challenging to machine, may cause greater tool wear during CNC processing. Both types resist oil, fuel, and many chemical solvents but perform poorly in strong acid environments.
Common Applications: Gears, bushings, fasteners, circuit board mounting hardware, electrical insulation, automobile engine compartment components, and industrial conveyor belt guides.
PC (Polycarbonate)
Similar to PMMA, PC is also a transparent thermoplastic but is 10~20 times more impact resistant, and is one of the toughest engineering plastics available. PC is easily processed by CNC machining, injection molding, and extrusion, and is suitable for drilling, cutting, and polishing. It also maintains dimensional stability and performs well over a wide temperature range (-40°C to 120°C). Its natural milky-blue tint and glossy finish can be dyed black for opaque applications, offering both functionality and aesthetics.
Pure polycarbonate has poor wear resistance and is prone to scratching. Anti-scratch coatings and vapor polishing can be added as a post processing step to improve wear resistance or optical clarity. It also has limited weather resistance and tends to yellow under prolonged UV exposure. Additionally, its cost is higher than that of general plastics like ABS, which can limit its use in large-scale applications.
Common Applications: Safety equipment like helmets and goggles, optical components such as lenses and LED covers, electronic housings, automotive parts like light covers, and construction materials like transparent roofing and sound barriers.
PEEK (Polyether Ether Ketone)
PEEK is a high-performance thermoplastic capable of withstanding extremely high temperatures—up to around 250°C, and even 300°C for short periods, far exceeding the thermal limits of most common plastics. It offers exceptional mechanical strength, rigidity, toughness, wear resistance, and chemical corrosion resistance. Its low moisture absorption ensures dimensional stability, and it also provides good biocompatibility.
Compared to other high-performance plastics, PEEK has a higher density . Despite its strong chemical resistance, prolonged exposure to UV light and oxygen may cause degradation. PEEK is also more expensive than most CNC plastics, due to both the high raw material costs and the complexity of the machining process.
Common Applications: Aerospace for engine components and seals, automotive for high-performance parts, medical for implants and instruments, chemical for valves and pumps, and electronics for cable insulation and connectors.
PVC (Polyvinyl Chloride)
PVC is an economical, easy-to-process, and practical plastic. It has strong resistance to acids, alkalis, salts, and organic solvents, and is an excellent electrical insulator. Due to its high chlorine content, PVC has impressive flame-retardant properties, making it a widely used material across various industries.
However, PVC has poor heat stability and can degrade or become brittle when exposed to high temperatures for extended periods. During processing, PVC may release harmful chlorine gas, so appropriate safety measures must be taken.
Common Applications: Drainage pipes, electrical cable insulation, infusion tubes, pharmaceutical packaging, consumer goods packaging, billboards and signs, as well as flooring materials, window frames, and door frames in building materials.
HDPE (High-Density Polyethylene)
HDPE stands for High-Density Polyethylene. Despite its name, HDPE is less dense than many engineering plastics (such as POM, PC, or PA). It offers excellent chemical resistance, electrical insulation, and maintains good impact resistance and toughness even at low temperatures. HDPE has an extremely low moisture absorption rate and is considered food-safe.
The main drawbacks of HDPE include relatively low heat resistance and poor UV stability. Additionally, its mechanical properties are slightly lower than some engineering plastics (like Nylon or POM), which may limit its performance in high-precision machining or under heavy load conditions.
Common Applications: Water pipes, food packaging, storage containers, agricultural irrigation systems, and chemical storage tanks.
PTFE/Teflon (Polytetrafluoroethylene)
PTFE, widely recognized by its brand name Teflon, is a white solid with an extremely low friction coefficient, often considered the lowest of any solid material. This means that PTFE parts typically do not require lubricants. Its ultra-low surface energy makes it highly resistant to contamination and effortless to clean. Additionally, PTFE is highly resistant to virtually all chemicals and has excellent heat resistance, capable of withstanding continuous exposure to temperatures up to 260°C (500°F). As a high-performance material, it is also an excellent electrical insulator.
However, PTFE has lower mechanical strength compared to other engineering plastics like PEEK or POM, and can be easily scratched or damaged. It also has a high coefficient of thermal expansion, and during high-temperature processing, it can release harmful gases. Therefore, precise machining of PTFE can be challenging.
Common Applications: Seals, pipe linings, and valves in the chemical industry; equipment for food processing and pharmaceuticals; electrical cables; as well as seals and insulation materials in the automotive and aerospace industries, and sliding components such as rails and bearings.
Helpful Considerations When Choosing a Plastic
From last section, we have an overall understanding of the common CNC plastics and may have noticed that different plastics vary significantly in their physical, mechanical, or chemical properties, which can affect the outcome of your project. Next, we’ll explain the various factors you should consider in plastic CNC machining.
Hardness and Strength
The hardness and strength properties of a specific plastic are important considerations to ensure it meets the requirements of its final application. High-hardness plastics typically offer better wear resistance, while high-strength plastics can withstand greater mechanical loads. Furthermore, these properties affect the way a material behaves during machining. Plastics with higher hardness and strength, such as POM, PEEK, and glass fiber-reinforced PA, tend to produce short, regular chips and achieve a high surface finish. However, they are more challenging to cut, and tool wear occurs more quickly.
In contrast, softer or lower-strength plastics, such as PP, PVC, and PTFE, generate long, stringy chips during machining, which can easily wrap around the tool. These materials are prone to adhesion and gouging, leading to surface quality issues.
Moisture Absorption and Reaction to Chemicals
Unlike most metals, which do not absorb moisture from the air under normal conditions, many plastics (such as PA and PC) absorb moisture from the atmosphere or cooling fluids. This can lead to dimensional expansion, affecting CNC machining precision. Moisture can also soften plastics, reduce their toughness, or release internal stresses, all of which impact the durability of the part. To prevent brittleness or machining defects, these plastics may need to be stored in air-conditioned rooms, sealed bags, or dried before machining.
On the other hand, plastics generally resist most acids, alkalis, and salts. For example, PTFE is virtually inert to all chemicals, even in harsh environments. However, some plastics, like ABS, are vulnerable to solvents such as acetone, which can dissolve the surface, while PC may crack under alcohols or alkaline solutions.
Appearance, Transparency, and Light Transmittance
For projects that require specific aesthetic or optical properties, the light transmittance of the material is a key consideration. Applications such as optical components and display covers demand materials with excellent transparency or specific optical characteristics, such as PMMA and PC, which offer high transparency.
However, machining can significantly impact a plastic’s optical performance. Even minor surface defects, scratches, or tool marks can reduce light transmittance and cause unwanted scattering, affecting optical clarity. To maintain high transparency and surface quality, fine cutting, polishing, or chemical treatments are often necessary .
Thermal Expansion and Heat Deflection Temperature (HDT)
Plastics expand when exposed to heat, a property measured by the Coefficient of Thermal Expansion (CTE). Compared to metals, plastics typically have a much higher CTE (50–250 × 10⁻⁶/°C vs. 10–25 × 10⁻⁶/°C for materials like steel and aluminum). The higher the CTE, the greater the dimensional changes caused by heat during CNC machining, which can affect precision. For high-precision applications, such as aerospace and medical devices, plastics with a high CTE, like POM and PTFE, may require design compensation to maintain accuracy. Alternatively, low-expansion materials, such as PEEK or glass fiber-reinforced composites, can help minimize thermal distortion.
Heat Deflection Temperature (HDT) measures a material’s ability to resist deformation under load at elevated temperatures. In general, a plastic’s HDT corresponds to its stiffness—materials with higher rigidity (such as glass-fiber-reinforced plastics and polyimides) tend to have higher HDT values, while more flexible polymers (like PE and PP) have lower ones. Plastics with higher HDT can remain dimensionally stable under load at higher temperatures, ensuring the part performs as intended. However, most plastics have an HDT significantly lower than metals. Their range typically falls between 50°C and 250°C, and only a few high-performance engineering plastics, such as PEEK and PAI, can reach around 300°C.
Conclusion
CNC plastics offer unique advantages over metals, including lower density, superior chemical resistance, excellent electrical insulation, and cost efficiency. Moreover, they are compatible with various manufacturing processes such as CNC machining, 3D printing, and injection molding.
We hope this guide has provided valuable insights to help you make an informed decision when selecting CNC plastics for your project. If you're unsure whether CNC machining or 3D printing is the right choice, or if you're seeking expert guidance and high-quality CNC machining solutions, contact Chiggo today—let’s get started!
Key Takeaways
Plastics are generally easy to CNC machine, and ABS offers one of the most cost-effective options for prototyping, manufacturing, and general-purpose applications, helping keep projects on budget.
Acetal (Delrin) is the most popular CNC-machinable plastic, valued for its strength, stiffness, and dimensional stability, particularly in precision parts for automotive, electronics, and industrial machinery.
Plastics like PEEK, PVC, HDPE, and FEP are excellent options for applications demanding strong chemical resistance.
Some heat-sensitive materials, such as PEEK and PVC, require careful temperature control during CNC machining to prevent material degradation or the release of harmful gases.
For applications requiring transparency, consider PC, Acrylic, or PET. However, be mindful of their thermal limitations.
A CNC mill is an excellent choice for machining plastics, but attention must be paid to mill speeds to avoid warping or melting heat-sensitive materials.
