When it comes to CNC machining of plastic parts, not all plastics are suitable—and choosing the wrong one can lead to warping, excessive tool wear, surface defects, or part failure. Whether you’re prototyping, testing fit and function, or producing low-volume parts, selecting the right plastic is a critical step.
In this guide, we’ll break down:
- Which plastics are commonly used in CNC machining
- Key differences in their properties and machinability
- How to choose the right material for your application
Which Plastics Are Commonly Used in CNC Machining?
The ideal plastic materials for cnc machining are those that offer good dimensional stability, machinability, and surface finish under subtractive processes. Below is a curated list of commonly used plastics in CNC machining, along with their key properties and typical applications.
Best CNC Machining Plastics Comparison: Properties & Machinability
| Material | Machinability | Heat Deflection Temp (°C) | Mechanical Strength | Dimensional Stability | Surface Finish | Cost Level | Key Traits |
|---|---|---|---|---|---|---|---|
| POM (Delrin) | ★★★★★ Excellent | ~100 | High | Excellent | Excellent | Medium | Strong, low-friction, ideal for precision parts |
| ABS | ★★★★☆ Very Good | ~80 | Moderate | Moderate | Good | Low | Low cost, impact-resistant, ideal for housings and prototypes |
| Nylon (PA6/PA66) | ★★★★☆ Good | ~120 | High | Moderate (moisture-sensitive) | Good | Medium | Self-lubricating, good for moving parts, absorbs moisture |
| PC (Polycarbonate) | ★★★☆☆ Average | ~135 | High | Excellent | Average | High | Clear and impact-resistant, but heat-sensitive during machining |
| PEEK | ★★★☆☆ Average | ~250 | Very High | Excellent | Good | Very High | High-performance, for demanding environments (medical, aerospace) |
| PTFE (Teflon) | ★★☆☆☆ Fair | ~260 | Moderate | Fair | Fair | High | Ultra-low friction, excellent chemical resistance, difficult to machine |
| HDPE | ★★★☆☆ Average | ~120 | Moderate | Fair | Fair | Low | Low-cost, good impact strength, but soft |
| PMMA (Acrylic) | ★★☆☆☆ Brittle | ~90 | Moderate | High | Excellent | Medium | Transparent and aesthetic, prone to cracking |
Typical Applications and What to Avoid
| Material | Ideal For | Not Recommended For |
|---|---|---|
| POM | Precision gears, guides, jigs, sliding parts | High-heat or bonded assemblies |
| ABS | Housings, brackets, basic functional parts | High-stress or load-bearing components |
| Nylon | Pulleys, bushings, wear pads | High-humidity environments or tight tolerance parts |
| PC | Transparent covers, electronic enclosures | Scratch-prone decorative parts |
| PEEK | Aerospace, medical, high-load/high-temp components | Cost-sensitive, low-spec parts |
| PTFE | Seals, bushings, anti-stick parts | High-tolerance or structural parts |
| HDPE | Fixtures, containers, sliding pieces | Precision parts with tight tolerances |
| PMMA | Light covers, display windows | Impact or load-bearing applications |
How to Choose the Right Plastic for CNC Machining?
When selecting a plastic for CNC machining, consider the following:
| Design Need | Recommended Material(s) |
|---|---|
| Tight tolerances | POM, PEEK |
| Wear or friction resistance | Nylon, PTFE |
| Transparency | PC, PMMA |
| High-temperature resistance | PEEK, PTFE |
| Budget constraints | ABS, HDPE |
| Smooth surface finish | POM, PMMA |
Practical Tips for Beginners
- For prototypes or first-time projects, start with ABS or POM — they are easy to machine and cost-effective.
- If tight tolerances are required, POM is your go-to option thanks to its excellent dimensional stability.
- Always prototype a single part before running full production — this helps test surface quality and tool compatibility.
If you’re unsure which plastic is right for your project, or you want expert advice based on your design and application, feel free to contact RJC Mold. We provide fast quotes and material recommendations based on real-world machining experience.
Learn more about our CNC machining services here.
