Sharpening a drill bit with a file involves carefully reshaping the cutting edges to restore their original sharpness and angle, allowing for more efficient and precise drilling. This process can significantly extend the lifespan of your drill bits, saving you time and money.
Why Sharpen Your Drill Bits?
Over time, drill bits become dull from use, leading to slower drilling, increased heat generation, and poor-quality holes. A dull bit requires more force, can wander off-center, and might even burn the material you're drilling. Sharpening them revitalizes their cutting ability, ensuring clean cuts and extending their service life.
Choosing the Right File
While various files can be used, a diamond file is particularly effective for sharpening drill bits due to its abrasive surface, which can handle hardened steel and carbide. Other suitable options include a high-quality machinist's file, such as a mill file or a double-cut flat file, especially for softer steels.
- Diamond File: Ideal for all types of drill bits, including those made of high-speed steel (HSS), cobalt, and carbide. Its fine grit allows for precise material removal.
- Mill File: Good for general-purpose sharpening of HSS bits.
- Flat File (Double-Cut): Can also be used for HSS bits, offering a more aggressive cut than a mill file.
Preparation is Key
Before you begin sharpening, ensure you have the right setup for safety and accuracy.
1. Safety First
- Eye Protection: Always wear safety glasses or goggles to protect your eyes from metal shavings.
- Gloves: Consider wearing work gloves for a better grip and to protect your hands.
- Stable Workspace: Secure your drill bit firmly. A drill bit sharpening jig or a vise can be invaluable for maintaining consistent angles.
2. Clean the Bit
Remove any debris, rust, or residue from the drill bit using a wire brush or an old rag. A clean bit allows you to clearly see the cutting edges and ensures the file makes proper contact.
3. Identify Key Angles
Understanding the anatomy of a drill bit is crucial for effective sharpening. The primary areas to focus on are:
- Lip Angle (Point Angle): This is the angle at the tip of the drill bit. For general purpose drilling, a 118-degree angle is common. Harder materials may require a wider angle (e.g., 135 degrees), while softer materials might benefit from a narrower one.
- Relief Angle (Clearance Angle): This angle ensures that the cutting edge, and not the heel of the bit, contacts the material. It typically ranges from 8 to 12 degrees. Without proper relief, the bit will rub instead of cut.
- Chisel Edge: The small, non-cutting edge at the very center of the drill bit's tip. While it doesn't cut, it helps center the bit.
Common Drill Bit Angles
| Drill Bit Type | Lip Angle (Point Angle) | Relief Angle | Best For |
|---|---|---|---|
| General Purpose (HSS) | 118° | 8-12° | Wood, soft metals, plastics |
| Harder Metals (Cobalt/HSS) | 135° | 10-15° | Stainless steel, hard alloys |
| Soft Materials (Plastics) | 90° | 15-20° | Acrylic, PVC (may require special geometry) |
The Sharpening Process with a File
The goal is to restore the original lip and relief angles on both cutting edges evenly.
Step-by-Step Sharpening
- Secure the Bit: Place the drill bit in a jig or vise, ensuring it's held firmly and stable. This is critical for maintaining consistent angles throughout the process.
- Position the File: Hold the diamond file (or chosen file) against one of the cutting edges. You need to file along the flute of the drill bit, moving from the tip towards the shank.
- Find the Angle: Angle the file to match the existing lip and relief angles of the drill bit. This usually means the file will be at about 59 degrees from the drill bit's center axis for a 118-degree point, and tilted slightly back to create the relief angle.
- File in One Direction: Move the file against the cutting edge in one direction only. Avoid filing back and forth, as this can dull the file and create an uneven edge. Apply light, consistent pressure.
- Time and Repeat: For effective sharpening with a diamond file, run the tool along the edge for approximately five seconds.
- Switch Sides: Now, turn the drill bit and file the other cutting edge. Run the file along this edge for five seconds, replicating the same angle and motion.
- Consistency is Key: Repeat this process seven or eight times for each side. The aim is to remove material evenly from both cutting edges until the blade feels smooth and sharp. Consistency ensures the tip remains centered and balanced.
- Check the Chisel Edge: The chisel edge at the very center should be small and nearly perpendicular to the flutes. If it's too wide, it will resist cutting.
Advanced Tip: Web Thinning (For Larger Bits)
For larger drill bits (typically 1/4 inch or larger), you might consider web thinning. This involves grinding a small amount of material from the chisel edge area to make it shorter and more effective. This reduces the force required to feed the drill, as the web is not a cutting edge.
- How to: Use a small, triangular file or the corner of a diamond file to carefully remove a small amount of metal from behind the chisel edge, narrowing its width. Be extremely cautious not to damage the main cutting edges.
Checking for Sharpness
After sharpening, inspect the drill bit carefully:
- Visual Inspection: Both cutting edges should be symmetrical, sharp, and free of nicks or burrs. The chisel edge should be centered.
- Feel Test: Carefully run your fingernail across the cutting edge. It should feel sharp and "catch" your nail, not slide smoothly.
- Test Drill: The ultimate test is to drill a hole. A properly sharpened bit will cut smoothly, produce continuous chips, and require minimal downward pressure.
Maintenance and Storage
To prolong the life of your sharpened bits:
- Clean After Use: Wipe down bits after drilling to remove debris.
- Lubricate: A light coat of oil can prevent rust, especially for HSS bits.
- Proper Storage: Store drill bits in a designated drill index or case to protect their cutting edges from damage and prevent dulling.
Sharpening your drill bits with a file is a practical skill that enhances your drilling precision and extends the life of your tools. With patience and practice, you can achieve excellent results, bringing your dull bits back to life.
