When drilling plastic, the optimal speed varies depending on the type of plastic, the drill bit diameter, and the specific application. However, for general drilling, especially for pilot holes, a moderate speed is often recommended to prevent melting and cracking.
What Speed Do You Drill Plastic?
For drilling pilot holes up to 1/2 inch in diameter in various plastics, it is generally best to use a drill speed between 600 to 1,000 revolutions per minute (RPM). This speed, combined with a positive feed rate, helps ensure clean holes and prevents material grabbing.
Recommended RPM Ranges for Different Plastics and Bit Sizes
While the 600-1,000 RPM range is a good starting point for pilot holes, drilling larger holes or specific types of plastic may require adjustments. The goal is to generate chips rather than a melted mess, which means finding a balance between speed and feed.
| Plastic Type | Drill Bit Diameter | Recommended RPM Range | Key Considerations |
|---|---|---|---|
| General Pilot Holes | Up to 1/2 inch | 600 - 1,000 RPM | Use a positive feed to prevent grabbing; crucial for maintaining structural integrity. |
| Acrylic (Plexiglass) | Small (up to 1/4") | 1,000 - 2,000 RPM | Use sharp, modified drill bits (e.g., zero rake angle, 60-90° point angle). |
| Medium (1/4" - 1/2") | 500 - 1,000 RPM | Minimize heat buildup to prevent crazing or melting. | |
| Large (> 1/2") | 200 - 500 RPM | Very slow speeds are critical to avoid cracking or chipping, especially near edges. | |
| Polycarbonate (Lexan) | Small (up to 1/4") | 1,000 - 2,500 RPM | Similar to acrylic, but generally more forgiving. Watch for gumming if speed is too low or feed too high. |
| Medium (1/4" - 1/2") | 600 - 1,200 RPM | Coolant (compressed air or water) can be beneficial for deep holes. | |
| PVC, HDPE, Nylon | Small (up to 1/4") | 1,500 - 3,000 RPM | Softer plastics can handle higher speeds, but watch for melting or stringing. |
| Medium (1/4" - 1/2") | 750 - 1,500 RPM | Aggressive feed rates can lead to grabbing; ensure secure clamping. | |
| Large (> 1/2") | 300 - 750 RPM | Ensure proper chip evacuation; peck drilling helps. |
Always test on a scrap piece of the same material before drilling your final project.
Importance of Feed Rate and Technique
Beyond speed, the feed rate—how quickly the drill bit advances into the material—is equally critical. For optimal results, a positive feed rate of 0.005 to 0.015 inches per revolution is advised. It's crucial to avoid hand feeding, as the drill can easily grab the material, leading to the formation of microcracks and a poor finish. Using a drill press with controlled feed is highly recommended.
Tips for Successful Plastic Drilling
To achieve clean, crack-free holes in plastic, consider these practical insights:
- Use Sharp Drill Bits: Dull bits generate excessive heat and can cause melting or cracking. Bits designed for plastic often have a steeper point angle (60-90 degrees) and a zero rake angle, which scrapes rather than cuts, reducing stress.
- Cooling is Key: Heat is the enemy when drilling plastic. Use compressed air to clear chips and cool the bit and material. For thicker plastics, a light mist of water or a specific cutting fluid for plastic can be beneficial.
- Secure Clamping: Always clamp the plastic workpiece firmly to your workbench or drill press table. This prevents the material from rotating or lifting, which can lead to cracking or injury.
- Peck Drilling for Deeper Holes: For holes deeper than the bit's diameter, use a peck drilling technique. Drill a short distance, retract the bit completely to clear chips and cool, then repeat until the hole is complete.
- Use a Backing Material: Place a piece of scrap wood or plastic beneath your workpiece. This provides support as the drill exits the material, preventing blowout and chipped edges.
- Start with a Pilot Hole: Even if you're drilling a large hole, starting with a small pilot hole (using the recommended 600-1,000 RPM and positive feed) can guide the larger bit and reduce stress.
By paying attention to speed, feed rate, and proper technique, you can successfully drill various types of plastic with professional results. For more detailed information on machining plastics, you can refer to resources like Plastics International's Machining Guide.
