Polypropylene (PP) is one of the easiest plastics to CNC machine. It has a low friction coefficient (0.1-0.2) and can be machined at speeds of 3000-5000 RPM, causing minimal tool wear, making it ideal for beginners.
Plastics That Are Easy to Machine With a CNC
Have you ever wondered which plastic is the best for CNC machining? I have some interesting data and experience to share. First, let’s take a look at those plastics—it’s like choosing a chocolate cake in a store, each one has its own characteristics and suitable scenarios.The latter is often made of polypropylene (PP). Why? This low tool wear-rate is generally suitable for cheap, free-machining materials. To be specific for PP, the friction coefficient is about 0.1-0.2 which is far smaller than other plastics like ABS (0.35-0.4). You can machine a 10mm PP sheet up to speed of 3000-5000 RPM, while the PVC oft is machined at an average range between 2000-3000 RPM.
Polyethylene (PE) has applications in almost all fields like food packaging to toys. PE is a very versatile material. One type is low-density polyethylene (LDPE), which is employed in applications where its lightness, superb chemical resistance, and wear resistance are beneficial. LDPE density is about 0.91-0.93 g/cm³ which is much lower than other plastics like PVC (1.38-1.41 g/cm³). LDPE tensile strength is 8-12 MPa versus HDPE at up to 20-30 MPa. Cutting speed for machining 50 mm diameter LDPE rod is 4000 RPM with material removal per pass of 1-3 mm.Polyoxymethylene (POM) or acetal is another material that people tend to underestimate. One of the advantages is that this plastic features high mechanical strength and rigidity, with very good results during machining. POM is cut with a cutting force of about 40-50 N, so it will also shape the material into high precision parts. Tensile strength: 60-70 MPa, Hardness: 85-90 Shore D. Machining to a sheet thickness of 20 mm with cutting speeds up to 3500 RPM and cutting depth usually between 2-4 mm. As the expert said, “POM is like Iron Man in the plastic world, looks so hard & tough.”
Finally, Polycarbonate (PC) aspect also needs to be mentioned here. PC has very high impact strength, as high as 70-80 kJ/m² (250 times the density of ordinary glass). Even though it needs better machining than other materials, the fact that it is transparent and resistant to impact makes it very interesting for optical devices or protective covers. For example, a 5mm thick PC sheet may be machined at cutting speeds of 3000-4500 RPM to reach an average depth of cut in the range from about 0.5 to 2 mm. If there’s a plastic that can survive no-holds-barred testing, it’s polycarbonate—as someone once said: “Polycarb the Wonder Plastic,” or words to that effect.
Best Plastic Types for Beginners to Machine on CNC
If you’re new to CNC machining, finding an easy-to-machine plastic is key. Trust me, these data will surprise you.First up is ABS plastic. Automotive parts, electronic product housings, etc.!! ABS hardness: 90-100 Rockwell R, processing temperature is about 200-250°C. A friend said, “The machining of ABS will not cause overall deformation without warping.” This has a tensile impact strength of 50-60 kJ/m² and performs well even at low temperatures. A 20 mm diameter ABS rod can be machined with a cutting speed of around 2500 RPM and also 1-2 mm depth cuts.
A good material is Nylon (PA), mainly PA6 and PA66. Nylon has high strength, wear resistance, and heat resistance with a tensile strength of 70-90 MPa, and temperature control to 100-120°C. Data shows that cutting speed can reach 3000-4000 RPM for machining nylon boards of about 10 mm thick, and the depth of cut allows 3-5 mm! Benefit: Nylon has a low friction coefficient of 0.2-0.25 and therefore minimally wears the tools in machining processes, resulting in longer tool life as compared to other polymers.It is a good material to start with, and that’s because of its availability everywhere; almost anything you think about making can at least get the shape right through acrylic (PMMA). Why? Due to the high transparency and easy cutting of it. PMMA offers a hardness from 90-105 Rockwell M and has a tensile strength of between 60-70 MPa. It is processed at 150-180°C and during machining of a PMMA sheet with the thickness of 5 mm, it can reach cutting speeds as high as 3500 RPM in conjunction with the cut depth between 0.5-1 mm. A professional in the industry once said: “PMMA of CNC proofing is like drawing on paper, simple and beautiful.”
Also, obviously PTFE is a good option. Chemically resistant and low friction coefficient (0.04-0.10). PTFE tensile strength is 20-35 MPa, processing temperature can reach up to 260°C. When machining a PTFE sheet with a thickness of 5 mm, the cutting speed can be as fast as 2000 RPM with a depth between 1-2 mm. As an old engineer recounts: “PTFE in the plastics world is just like Teflon, non-stick and no-wear.”Last but certainly not least, is the high-density polyethylene (HDPE). HDPE has a density of 0.94-0.97 g/cm³ which makes it more durable than low-density polyethylene (LDPE). It has a tensile strength of 25-35 MPa with a processing temperature of 130-160°C. You can machine an HDPE rod with a diameter of 1 inch at a cutting speed of about 3000-4000 RPM, with a typical depth of cut between 1-3 mm. The friction coefficient of HDPE is about 0.2, so it has better smoothness and is easy to control during the process.
Common plastic materials
Do you know which plastics are best for CNC machining? I have experiences and data to show.
We will be discussing some of the popular plastic materials prevalent. The materials from which a drip tray is made are ABS plastic, mainly used in automotive parts or housings for electronic goods. ABS has a Rockwell R hardness of 90-100, and the processing temperature ranges from about 200 to 250 °C (400…480° F). One of my friends said that “machining ABS will not warp at all.” Material with tensile impact strength 50-60 kJ/m², ideal for low-temperature applications. ABS Rod 20mm Diameter – machining at speeds of approx. 2500 RPM with a depth cut between about ~1-2 mm.Nylon (PA) is another excellent material, especially PA6 and PA66. High strength, wear resistance, and heat resistance are some of its features. In terms of tensile strength: nylon has a tensile strength of 70-90 MPa; in terms of temperature control, the temperature setting should be around 100-120 degrees. Data shows that when processing a board with thickness up to 10 mm, for cutting speed straight piece helical column can reach 3000-4000 RPM. With side depth meters adjusted, preferably 3-5 mm cut-depth. Nylon has a very low friction coefficient, 0.2-0.25, which means significantly less tool wear, making tools last much longer compared to other polymers.
Let me just discuss acrylic (PMMA) one last time. This is a good choice of material since it is so abundant everywhere. Its transparency is high, and it can be cut well. Its Rockwell M hardness number ranges between 90-105, and its tensile strength is around 60-70 MPa. It is processed at 150-180° C. For cutting a 5 mm thick PMMA sheet, the rotation decreases to about 3500 RPM and the depth of cut ranges from 0.5 – 1 mm. As an industry expert might say: “PMMA and CNC coloring is like drawing on paper – simple and pretty.“PTFE is also noteworthy because it is resistant to chemicals and has a low coefficient of friction (0.04-0.10). PTFE can achieve a tensile strength of 20-35 MPa, and its processing temperature is ≤260°C. The cutting dimension should be about 5 mm thickness, with the speed of the blade reaching 2000 RPM, and the cut depth should be between 1~2 mm. A former plastic industry engineer joked: “The old saying goes that PTFE in the plastics world is just like Teflon, non-stick and no wear!”
Lastly, but most definitely not least, is High Density Polyethylene (HDPE). HDPE has a linear density of 0.94–0.997 g/cm³, which makes it more rigid than low-density polyethylene (LDPE). It offers a tensile strength of between 25 and 35 MPa, with recommended processing temperatures around 130–160°C. You can machine HDPE rod punches averaging about one inch in diameter at speeds ranging from three to four thousand RPMs and typical cutting depths measuring between one to two millimeters across the workpiece surface area. HDPE has a friction coefficient of about 0.2, making it smoother and easier to adjust during the process. HDPE is arguably the easiest to machine material out there, making it ideal for beginners. For practical use, HDPE can be used as pipe material and toy packaging bottles, offering chemical resistance at a low price.
