This article is part of the CNC Machining Materials Guide: Metals, Plastics & Superalloys on CNX Precision.
Clear plastic machining turns transparent engineering plastics into lenses, guards, and display components. The two most common choices are acrylic and polycarbonate. Both offer clarity, but they behave very differently in service. This guide explains clear plastic machining and helps you choose between acrylic and polycarbonate for your next part.
Acrylic gives superior optics. Polycarbonate gives superior toughness. The clear plastic machining comparison starts with impact and optics. Understanding the trade-offs prevents costly mistakes.
Acrylic vs Polycarbonate: Key Differences
The table below compares the two materials across the properties that matter most.
| Property | Acrylic (PMMA) | Polycarbonate (PC) |
|---|---|---|
| Light transmission | About 92 percent | About 88 percent |
| Impact strength | Low, brittle | Very high |
| Scratch resistance | Better | Softer, scratches easier |
| UV resistance | Excellent | Good with coatings |
| Chemical resistance | Moderate | Poor against solvents |
| Machinability | Easy, polishable | Good, tougher chips |
| Typical use | Displays, lenses | Guards, housings |
Acrylic transmits more light and resists scratches better. Polycarbonate absorbs impact that would shatter acrylic. These differences drive most material decisions in clear plastic machining.
Temperature limits differ as well. Acrylic softens around 80 degrees C. Polycarbonate holds its shape to roughly 120 degrees C. Weight is close, with acrylic slightly lighter. Both materials cost more than glass but weigh less and resist shattering. These factors narrow the choice further.
When to Choose Acrylic
Choose acrylic when optical quality is the priority. It transmits more light with less distortion. This suits display panels, instrument windows, and retail showcases.
Optical clarity also matters for instrument covers. Gauge faces stay readable through acrylic. Light guides distribute LED light evenly. Retail displays show products without tint. In each case, the material’s transmission is the deciding factor.
Acrylic also resists UV and weather better. Outdoor signage stays clear for years. Scratches are less likely, which matters for surfaces that people touch. The material is easier to polish, so transparent edges are simpler to produce.
Acrylic also accepts secondary processes well. It lasers, engraves, and cements cleanly. Edges can be flame polished to a glass-like finish. This makes it ideal for display products where appearance drives the sale. The same properties speed up prototyping and sampling.
Choose acrylic when weight matters. It is slightly lighter than polycarbonate for the same volume. For large display panels, this difference adds up. For display-grade parts, clear plastic machining of acrylic is the classic route.
Think about handling as well. Acrylic parts ship well when protected with film. Polycarbonate tolerates rougher handling but still benefits from care. Tell your supplier how the parts will be used. This helps them choose packaging and handling steps.
- Display cases and signage
- Lenses and optical windows
- Retail and museum fixtures
- Light guides and LED covers
When to Choose Polycarbonate
Choose polycarbonate when impact resistance is critical. It can be far more impact-resistant than glass in many forms. Machine guards, safety shields, and protective covers rely on this toughness.
Polycarbonate also handles higher temperatures than acrylic. It keeps its shape where acrylic softens. Its dimensional stability is good, so parts hold tolerance under load. Clear plastic machining of polycarbonate is standard for these parts.
Polycarbonate also dampens vibration better than acrylic. This suits equipment with moving parts and noisy environments. It retains impact strength at low temperatures. Cold-climate glazing and vehicle parts benefit from this behavior.
However, polycarbonate scratches more easily and can crack under chemical stress. Solvents, cleaners, and even some adhesives cause crazing. Protect surfaces with hard coatings or choose a coated grade for demanding service.
Fasteners and assembly differ too. Polycarbonate accepts inserts and hardware without cracking when designed well. It drills and threads with less risk than acrylic. Mounting holes can be placed closer to edges. These advantages simplify mechanical design for enclosures.
- Machine guards and safety shields
- Protective housings and covers
- Transportation and industrial glazing
- High-temperature clear parts
Clear Plastic Machining Tips for Both Materials
Both acrylic and polycarbonate need careful machining, but the risks differ. Acrylic chips and cracks. Polycarbonate melts, gums, and stresses. The tips below address both.
- Use sharp carbide tools with polished flutes.
- Climb mill to reduce chipping on acrylic edges.
- Use coolant to prevent melting and gumming.
- Drill pilot holes and peck-drill deep holes.
- Reduce clamping pressure to avoid stress cracks.
- Polish edges for optical clarity where required.
Thermal expansion matters in clear plastic machining. Plastics expand several times more than metal. A large acrylic panel changes size noticeably with temperature. Design mounting holes with clearance to allow movement.
Watch how parts are stacked and stored. Clear plastics scratch easily in contact. Use paper or film between finished parts. Store them flat to avoid warping. A little discipline in the shop protects the optical quality you paid for.
Surface finish controls appearance. Milled edges look frosted. Flame polishing restores transparency on acrylic. Polycarbonate edges can be diamond-polished or flame-finished. Specify the desired edge finish in your drawing.
Drilling deserves special mention. Clear plastics crack at hole exits. Support the exit side with a sacrificial backing plate. Peck-drill deep holes to clear chips. Keep drill speeds moderate to avoid melting. These practices apply to both materials.
Tolerances also differ. Acrylic holds about plus or minus 0.1 mm on standard parts. Polycarbonate holds similar values when supported well. Both materials need stress relief between heavy cuts. At CNX Precision, we apply these practices to deliver clear parts that meet spec.
Inspection lighting reveals flaws. Hold the part against a light source and look for cracks, marks, and internal stress. An experienced inspector catches issues before shipping. This step is especially valuable for optical parts. It protects your reputation and your customer’s product.
Frequently Asked Questions
Which clear plastic is stronger?
Polycarbonate is far stronger under impact. Acrylic is stronger against scratching and UV. Choose based on the failure mode you fear most.
Can clear plastic machining produce polished edges?
Yes. Flame polishing and diamond polishing produce transparent edges on both acrylic and polycarbonate. Specify the finish in your drawing.
Is acrylic or polycarbonate better for outdoor use?
Acrylic resists UV naturally and stays clear longer outdoors. Polycarbonate needs UV coatings to avoid yellowing. For outdoor parts, acrylic is usually the better value.
Conclusion
Clear plastic machining gives you two strong options. Choose acrylic for optics, UV resistance, and easy polishing. Choose polycarbonate for impact resistance and temperature performance. Match the material to the application, not the other way around.
For reference, machining standards such as the ASTM material standards define the quality and tolerance requirements we follow.
CNX Precision machines both acrylic and polycarbonate to tight standards under ISO 9001 quality systems. Our team will recommend the right grade and finish for your product. Send your drawings today for a fast quote.