How to Turn Acrylic on a Lathe?

Turning acrylic on a lathe involves careful cutting, sanding, and polishing techniques to achieve a smooth, finished surface.

Turning acrylic differs from woodturning in several key ways. Acrylic, being a plastic, melts or chips if not cut properly, requiring sharp tools, specific speeds, and a focus on generating long, continuous shavings rather than dust.

Essential Steps for Turning Acrylic

Turning acrylic successfully requires attention to detail throughout the process, from mounting the blank to the final polish.

1. Preparation and Mounting

• Choose the Right Blank: Select cast acrylic blanks, which are generally easier to turn than extruded acrylic.
• Secure Mounting: Ensure the acrylic blank is securely mounted on the lathe using a chuck or between centers. A solid mount prevents vibration and ensures safety.
• Safety First: Always wear safety glasses or a face shield. Acrylic dust can be irritating.

2. Turning (Cutting)

• Tool Selection: Use sharp, high-speed steel (HSS) or carbide tools specifically designed for plastics or with a high positive rake angle. Scrapers work well.
• Tool Sharpness: Critical – Tools must be razor-sharp. Dull tools will scrape, generating heat and potentially melting the acrylic or causing chipping.
• Cutting Speed: Start with a moderate speed. Too slow can cause chipping; too fast can cause melting. Adjust based on the cut and material response.
• Technique:
  • Apply light pressure.
  • Take shallow cuts.
  • Aim for long, continuous shavings. This indicates the tool is cutting cleanly.
  • Move the tool smoothly and consistently.

3. Sanding

Sanding is crucial for removing tool marks and preparing the surface for polishing. It's a gradual process starting with coarse grits and moving to very fine ones.

• Start Coarse: Begin with a grit like 180 or 220.
• Lathe Running Method (Referenced Technique): As noted in the video reference, you can begin sanding with a 180 grit abrasive sanding in a side to side motion with the lathe running. This helps remove deeper marks quickly.
• Hand Sanding (Referenced Technique): To eliminate circular scratch patterns left by sanding with the lathe running, stop the lathe. And sand the blank by hand to remove the circular marks before moving to the next finer grit.
• Gradual Progression: Increase grits incrementally (e.g., 220, 320, 400, 600, 800, 1200, up to 2000 or even 4000). Sand at each grit until all marks from the previous grit are removed.
• Wet Sanding: Wet sanding, especially with finer grits, helps reduce heat buildup and prevents the sandpaper from clogging, resulting in a smoother finish. Use water or a dedicated plastic lubricant.

4. Polishing

Once sanding is complete, polishing brings out the clarity and shine of the acrylic.

• Polishing Compounds: Use plastic-specific polishing compounds or pastes. Apply a small amount to a soft cloth or a buffing wheel mounted on the lathe.
• Buffing: With the lathe running at a moderate speed, gently buff the surface with the compound. Use different buffing wheels or clean cloths for different stages of polishing if necessary.
• Heat Management: Be mindful of heat generated during buffing; excessive heat can melt the surface.

5. Finishing

A final step might involve a very fine polish or a protective wax designed for plastics, depending on the desired outcome.

Table: Recommended Tools & Materials

Turning acrylic requires patience, especially during the sanding and polishing phases, but the result is a clear, smooth, and often stunning finish.