Plexiglass is widely used in advertising signage, medical devices, electronic products, and industrial shielding due to its high light transmittance, strong weather resistance, and aesthetic appeal. However, during actual CNC machining, acrylic is prone to issues such as burrs, edge chipping, cracking, or even thermal melting and sticking to the cutter.
Combining professional CNC machining experience with scientific operational standards, this article breaks down the complete process—from tool selection and cutting parameter configuration to cooling, chip removal, and post-processing—to help you achieve high-precision, high-gloss acrylic machining.
Why Does Plexiglass Machining Require a “Scientific Method”?
Plexiglass is a thermoplastic, and its physical and thermal properties differ significantly from those of metals or hard woods. Understanding its material characteristics is essential for developing a proper machining plan:
Low Heat Deflection Temperature: Acrylic has a relatively low melting point and easily softens under the heat generated by high-speed cutting. If chip removal is poor or cooling is insufficient, chips will re-weld to the workpiece or tool (known as “tool burning”).
High Brittleness: Compared to other engineering plastics, acrylic is prone to stress cracking (crazing) or edge chipping under uneven stress or sudden impacts.
High Optical Clarity Requirements: Many acrylic components require highly polished edges or overall transparency, which places strict demands on post-machining surface roughness.
Therefore, abandoning traditional methods like cutting with utility knives or blindly applying metal-machining parameters in favor of scientific CNC machining strategies is key to ensuring finished product quality.
Core Technical Points for CNC Machining Acrylic
To achieve flat, burr-free, and near-transparent cut edges, precise control across three dimensions—cutting tools, parameters, and cooling systems—is required.
Tool Selection: Single-Flute End Mills Are Preferred
Recommended Cutter: Using a single-flute end mill specially designed for plastics is strongly recommended. Single-flute cutters feature a large chip flute space, allowing generated plastic chips to be evacuated quickly and effectively reducing frictional heat build-up.
Sharpness Requirement: The cutting edge must be extremely sharp. The sharper the blade, the less drag and stress concentration occur during cutting, resulting in a smoother finish.
Common Mistakes:Never attempt to use utility knives, standard dual-flute/multi-flute steel cutters, or worn tools. These lead to rough cuts and cause material melting due to poor chip evacuation.
Parameter Configuration: Balancing Spindle Speed and Feed Rate
The primary goal of cutting parameters is to “cut without generating excessive friction heat.”
Spindle Speed: Recommended between 12,000 and 15,000 RPM. Excessively high speeds cause severe frictional heat, while speeds that are too low can cause excessive cutting force, leading to edge chipping.
Feed Rate: Recommended at around 500 mm/min. Maintaining a stable feed rate ensures an appropriate chip load per tooth, preventing friction from moving too slowly or crushing the material from moving too fast.
Cooling and Chip Evacuation: Maintaining Low Temperatures and Clean Cuts
Cooling Method:Continuous cooling must be applied during machining. Air blast or mist cooling is recommended.
Key Functions:
Temperature Control:Timely removal of cutting heat prevents edge burning or softening.
Chip Clearance: High-pressure air rapidly blows chips away from the cutting zone, preventing re-cutting, scratches, or tool sticking.
From CNC Roughing to Mirror Polishing: The Complete Process
While scientific CNC milling produces clean, flat edges, achieving optical-grade transparency (a mirror finish) requires systematic polishing and post-processing steps.
CNC Finishing Stage
After roughing removes most of the stock, leave a margin of about 0.1 to 0.2 mm for a high-speed, light finishing pass. The finish pass eliminates tool marks left by rough machining, establishing a solid foundation for polishing.
Mechanical Sanding and Polishing
Sandpaper Sanding:Use progressively finer wet sandpaper with water to gradually remove minor surface scratches.
Buffing Wheel Polishing:Use a soft buffing wheel paired with acrylic-specific polishing compound (such as green or white compound) at high speeds to quickly restore surface gloss.
Flame and Solvent Polishing
Flame Polishing: Uses a hydrogen-oxygen flame to briefly melt an extremely thin surface layer of the acrylic, utilizing surface tension to create a mirror-like gloss upon cooling. Move the flame tip continuously to prevent overheating and bubbling.
Solvent Polishing:For complex internal cavities or tubing, solvents like dichloromethane can be used for vapor or wipe polishing. Proper ventilation and safety precautions are required.
Troubleshooting Common Issues
If processing quality issues arise during production, consult the following table for troubleshooting:
| Issue | Potential Cause | Recommended Solution |
| Melting / Tool Sticking at Edges | Poor chip evacuation, spindle speed too high, or lack of cooling | Lower RPM, activate air blast/mist cooling, switch to a single-flute cutter |
| Edge Chipping / Cracking | Dull tool edge, feed rate too fast | Replace with a new sharp cutter, lower the feed rate |
| Deep Tool Marks on Surface | Insufficient machine rigidity or mismatched feed parameters | Perform a light finishing pass, optimize chip load per tooth, and improve clamping |
By selecting single-flute cutters, setting parameters to 12,000–15,000 RPM with a 500 mm/min feed rate, and pairing them with effective air blast cooling, you can achieve efficient, high-quality CNC cuts on plexiglass (acrylic), laying a solid foundation for subsequent optical-grade polishing.