How to Sharpen an Auger Drill Bit (Using Auger Bit File)

An auger bit is an essential woodworking tool that bores deep, clean holes with excellent control. Over time, however, the cutting edges can become dull, reducing efficiency and hole quality. The good news is that you don't need to replace a dull bit; you can easily restore it.

This guide will walk you through the process of sharpening an auger bit using a specialized auger bit file, which is designed to precisely sharpen the bit's unique cutting geometry without damaging its crucial parts.

What is an Auger Bit File?

An auger bit file is a specialized metal file used specifically for sharpening auger drill bits.  It is a single-sided file with teeth designed to fit the tight spaces of an auger bit's cutting spurs and tips. Its unique shape allows you to sharpen the cutting blades without accidentally filing the bit's flights or the central guide screw.

Step-by-Step Guide to Sharpening an Auger Bit

The sharpening process is divided into two main parts: sharpening the cutting spurs and tips, and cleaning/sharpening the guide screw.

Part 1: Sharpening the Cutting Spurs and Tips

This is the most critical part of the process, as the sharpness of the spurs and tips determines how well the bit cuts.

Step 1: Sharpen the Spurs

Sharpen the inside edge of each spur, which are the small, sharp points on the outer edge of the bit that scribe the circumference of the hole.

• Hold the auger bit securely in a vise.
• Position the auger bit file to follow the existing angle of the inner surface of the spur.
• Make several smooth, consistent strokes, filing only the inside surface.
• Do not file the outside of the spurs. Filing the outside will reduce the diameter of the hole the bit drills and can permanently damage the bit's geometry.
• Ensure both spurs are filed to the same height and sharpness.

Step 2: Sharpen the Cutting Tips

The cutting tips are the small, sharp blades that are positioned at the base of the spurs, next to the guide screw.

• Carefully position the auger bit file to sharpen the top surface of each cutting tip.
• Ensure the tip's cutting edge is at the proper angle. It's often helpful to mark the original angle with a pencil.
• Stroke the file several times until the tips are sharp. Be consistent with the angle for both tips.

Step 3: Test the Sharpness

Test the bit on a piece of scrap wood to ensure the tips and spurs are properly sharpened. A properly sharpened auger bit should effortlessly pull itself into the wood and produce a clean hole with fine shavings. If the bit is still struggling, repeat the sharpening steps on the spurs and tips.

Part 2: Restoring the Guide Screw

The guide screw is the small, threaded point at the very center of the bit. While it doesn't cut the wood, it's essential for pulling the auger bit into the material and maintaining its position. Over time, the threads can get packed with dirt or become dull.

Step 1: Create a Reservoir

Drill a hole into a block of softwood just deep enough for the guide screw to fully enter. Remove the bit and keep this hole accessible.

Step 2: Apply Grinding Paste

Apply a small amount of a fine grinding paste to the guide screw threads using a toothbrush or a small stick. Also, apply some paste inside the softwood hole you just drilled.

Step 3: Use the Hole to Sharpen

Reinsert the guide screw into the paste-filled hole. Using the drill, run the bit forward and backward several times. This action will use the grinding paste and the wood to clean and lightly sharpen the threads of the screw.

Step 4: Clean the Bit

Remove the bit and wipe off all the excess grinding paste with a clean microfiber cloth. Rinse the bit with water to remove the water-soluble paste, then dry it completely to protect against rust.

Conclusion

By following these simple steps, you can easily restore your auger bits to their original sharpness using just an auger bit file and some grinding paste. This not only increases the efficiency and lifespan of your tools but also ensures you get cleaner, more precise holes in all your woodworking projects. A sharp auger bit is a safer and more effective tool, making this a worthwhile skill for any woodworker to learn.