DIY: Plastic Machining

Plastic can be machined with conventional woodworking tools.

Plastic is an extremely durable and affordable machining material used in nearly every industry. Therefore, machine shops and hobbyists need to know how to work with plastics in order to fabricate parts. While plastic can be shaped and cut like wood, specific techniques must be employed when machining this material. Unlike wood, plastic has a low melting point which can make machining difficult. Use a few basic professional fabrication techniques to machine plastic easily.

Things You'll Need

• Tape measure
• Grease pencil
• Table saw
• Electric drill
• Drill bits
• Table router
• Flush-trim router bit
• Electric sander
• Sandpaper
• Utility knife

Instructions

1. Leave the protective backing on the plastic to avoid scratching. Size the plastic for cutting using a tape measure. Because cutting leaves a rough edge and must be sanded, the plastic must be over-sized by 1/16-inch in length and width. Use a grease pencil to mark the desired length and width.

2. Ensure a square cut and avoid melting the plastic by cutting it with a table saw. Push the plastic into the saw blade at a rate of 10 to 20 feet per minute, using the saw’s fence to guide the material through.

3. Remove saw marks created during the cutting process, using a table router. Set the router’s fence so the router will remove 1/32-inch of material on each side of the rough-cut plastic. Push the saw-cut edge along the router’s fence. Route each of the four rough sides once.

4. 

   Use a grease pencil to lay out any cutouts.

   Mark any holes or cutouts for drilling on the material once the plastic has been routed. Use a grease pencil, which can easily be wiped off. Make sure cutouts and holes are marked with a clean line.

5. 

   A drill press is the best tool for hole cutting.

   Choose drill bits designed for plastic. Acrylic has a tendency to crack under pressure, especially when drilling through it. The correct drill bit will have a long sharp point. Set the drill at a medium speed. Place the point of the bit on the plastic. Gently push down on the drill, releasing the pressure as soon as the drill bit bites into the plastic.

6. Machine a clean cutout by using a router. Use scrap plastic or lumber to create a routing guide. Use a flush-trim router bit to create the cutout. The bit’s bearing will ride along the guide, creating a smooth edge. Set the table router bit's height so the bearing’s entire side is even with the guide. Set the router’s speed to 22,000 rpm.

7. Sand the routed edges of the plastic, using an electric palm sander and 220-grit sandpaper. Allow the sander’s weight to apply the necessary pressure, rather than pushing down on it.

8. Cut a beveled edge using a sharp utility knife. Hold the blade at a 45 degree angle to the edge being scraped. In a single long pass, pull the blade along the edge of the plastic.

References

• Plexiglass Sheet Info; Acrylite Plus Fabrication Manual PDF Download
• Boedeker Plastics; Guide to Plastics Machining
• Plastics Fabrication; Plastic Fabrication