How to Drill and Cut Carbon Fiber Cleanly

Carbon fiber isn't hard to cut, but it punishes the habits that work on wood and metal. The fibers are abrasive and dull ordinary drill bits fast. The layers want to split apart where the tool exits. Too much heat burns the resin. And the dust is fine, itchy and electrically conductive. This is what gives clean holes and edges.

Use the right tools

For drilling, use carbide or diamond-coated bits. A high-speed steel bit will cut a few holes and then start burning and tearing. Brad-point and dagger-style drills, which are made for composites, cut the fibers cleanly at the rim instead of pushing them out. For holes bigger than about 10 mm, a diamond-grit hole saw works well.

For cutting, a diamond or abrasive cutoff wheel, or a fine-tooth carbide router bit, gives a much cleaner edge than a saw blade with teeth. For production, waterjet cutting and CNC routing with diamond-coated tools are the usual choices.

Support the exit side

Most damage happens as the drill breaks through. The last plies have nothing behind them, so they push out and split. Clamp a sacrificial backing board tight against the exit side, and put masking tape over both faces where you're drilling. Drill from the face that matters most.

Fast spindle, light feed

Run the drill fast and let it cut. Push too hard and you get heat, frayed fibers and delamination. Ease off just before breakthrough. Peck in and out on thick parts to clear dust and let the tool cool.

Finish the edges

Sand edges with fine paper, ideally wet, which also keeps the dust down. Then seal the cut edge with a thin coat of epoxy or clear coat, so the exposed fibers don't fray or pick up moisture.

Take the dust seriously

• Extract dust at the tool, not after it's in the air.
• Wear a properly fitted respirator rated for fine particles, plus eye protection.
• Cover your arms. The fibers itch.
• Keep the dust away from electronics. It conducts and can short them out.
• Clean up with a vacuum that has a fine filter, not compressed air.

When to stop doing it by hand

If you're trimming more than a few parts, or the holes have to line up with something, a CNC router or a drill and trim fixture pays for itself quickly. The holes end up in the same place on every part and the edges are consistent. We cover that in how to prototype a carbon fiber part, and our composites work includes machined and trimmed parts.