Can you sharpen drill bits on a bench grinder? Yes, you can sharpen drill bits on a bench grinder, and it’s an effective way to bring dull bits back to life, saving you money and ensuring better drilling performance. This guide will walk you through the process step-by-step, making it accessible even for beginners.
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Why Re-sharpen Drill Bits?
Over time, drill bits become dull from use. This dullness leads to several problems:
- Slower Drilling: A dull bit requires more force, making drilling take longer.
- Increased Heat: Friction from a dull bit generates excess heat, which can damage the workpiece and the bit itself.
- Poor Hole Quality: Dull bits often create ragged holes with burrs, which need extra cleanup.
- Increased Effort: You’ll find yourself pushing harder, which can lead to fatigue and accidents.
- Damage to Workpiece: A dull bit can wander, creating off-center holes or damaging the surface of your material.
Re-sharpening drill bits is a cost-effective way to maintain your tools and ensure precision in your projects. It’s much cheaper than constantly buying new bits.
Essential Tools and Safety Precautions
Before you start, gather these items:
- Bench Grinder: A sturdy bench grinder is the core tool.
- Grinding Wheels: Ensure your bench grinder has appropriate grinding wheels. For most metal drill bits (like HSS drill bits), a standard aluminum oxide wheel is suitable. For carbide drill bits, a silicon carbide wheel is necessary due to their hardness.
- Bench Grinder Safety Glasses: Always wear safety glasses.
- Face Shield: A face shield offers extra protection.
- Gloves: Heavy-duty work gloves protect your hands from heat and sharp edges.
- Coolant or Cutting Fluid: This is crucial for preventing overheating of the drill bit. You can use water, specialized cutting fluid for grinding, or even a light oil.
- Drill Bit Sharpening Jig (Optional but Recommended): While you can freehand, a drill bit sharpening jig significantly improves accuracy and consistency, especially for achieving the correct drill point angle.
- Vice Grips or Pliers: To hold smaller bits if not using a jig.
- Marking Pen: To mark the cutting edges.
Bench Grinder Safety First
Working with a bench grinder requires strict adherence to safety rules.
- Eye Protection: Always wear safety glasses and consider a face shield. Sparks can fly unexpectedly.
- Secure the Grinder: Ensure the bench grinder is firmly mounted to a workbench or stand. A wobbly grinder is dangerous.
- Inspect Wheels: Before turning on the grinder, check the grinding wheels for cracks or damage. Do not use damaged wheels.
- Guard Placement: Make sure the wheel guards are properly in place and adjusted.
- Work Rest Adjustment: Adjust the work rest so it’s close to the grinding wheel (about 1/8 inch or 3mm) but not touching.
- Avoid Loose Clothing: Tie back long hair and avoid loose clothing that could get caught in the spinning wheel.
- Let Wheels Spin Up: Allow the grinder wheels to reach full speed before starting to grind.
- Keep Area Clean: Remove flammable materials from the vicinity of the grinder.
- Use Coolant: Never grind without coolant, especially for HSS bits. Overheating will ruin the temper of the steel.
- Don’t Force It: Let the grinder do the work. Forcing the bit can lead to uneven sharpening and wheel damage.
- One Person at a Time: If others are nearby, ensure they are aware of what you are doing and maintain a safe distance.
Getting Started: Preparing Your Bench Grinder
- Wheel Selection: For sharpening most common metal drill bits made of High-Speed Steel (HSS), a standard aluminum oxide grinding wheel is appropriate. If you’re working with harder materials like carbide, you’ll need a silicon carbide wheel.
- Wheel Mounting: Ensure the wheels are securely mounted and the grinder is unplugged while you make any adjustments.
- Work Rest Adjustment: Position the work rest so it’s a short distance from the grinding wheel. This provides support for the drill bit or the jig.
- Coolant Setup: If using a trough of coolant, ensure it’s positioned so you can easily dip the bit or soak the wheel. If using a spray, have it ready.
Sharpening Drill Bits Without a Jig (Freehand Method)
This method requires a steady hand and practice. It’s best for simple sharpening when a perfect angle isn’t critical.
Step-by-Step Freehand Sharpening
- Select Your Bit: Choose a bit that needs sharpening. For practice, start with a larger diameter bit.
- Set the Grinding Wheel Angle: The ideal grinding wheel angle for sharpening drill bits is generally around 59 degrees. This is the standard drill point angle for most common bits. While you can’t perfectly set this on a freehand grinder, aim to hold the bit at this approximate angle relative to the wheel.
- Prepare the Bit: You might want to mark one of the cutting edges with a marker to help you track your progress.
- Cooling: Dip the drill bit in coolant or keep a stream of coolant directed at the point of contact during grinding. This is critical.
- Grinding Technique:
- Hold the drill bit firmly with pliers or vice grips, with the shank extending out.
- Bring the cutting face of the bit to the grinding wheel.
- Angle the bit so the side of the flute is touching the wheel.
- The point of the bit should be held at the correct drill point angle. You are grinding the relief angle behind the cutting edge.
- Gently move the bit back and forth across the wheel in a sweeping motion to create a consistent bevel.
- Alternate between the two cutting edges. Grind one side for a few seconds, then switch to the other side.
- Dip the bit in coolant frequently. Overheating will ruin the bit.
- Continue grinding, checking your progress visually and by feeling the sharpness. You want to remove just enough material to create a new, sharp cutting edge.
- Checking the Angle: Look at the tip. You want two symmetrical cutting edges. The angle between them should be the standard 118 degrees (or 135 degrees for specific applications). The relief angle behind the cutting edge should be consistent.
- Refine the Point: Once both cutting edges are sharp, you may need to grind the chisel edge (the thin, flat edge at the very center of the point) to a very slight bevel. Be careful not to grind away too much material here. The goal is to have the cutting edges meet at a sharp point.
- Test the Bit: Carefully test the sharpened bit on a piece of scrap material. It should cut cleanly and with less effort.
Sharpening Drill Bits with a Drill Bit Sharpening Jig
Using a drill bit sharpening jig makes the process much more accurate and repeatable. There are various types, but most work on a similar principle.
Types of Drill Bit Sharpening Jigs
- V-Block Jigs: These typically have a V-shaped slot that holds the drill bit at the correct angle. You then pivot the jig against a guide on the grinding wheel.
- Collet Jigs: Similar to a drill press chuck, these hold the bit in a collet and guide it against the wheel.
- Wheel-Mounted Jigs: Some jigs are designed to mount directly onto the grinder’s wheel arbor, providing a more integrated sharpening station.
Step-by-Step Sharpening with a Jig
- Read the Jig’s Instructions: Each jig is slightly different. Always start by reading the manufacturer’s manual.
- Install the Jig: Mount the jig onto your bench grinder according to its instructions.
- Set the Angle: Adjust the jig to the desired drill point angle. For most HSS bits, this is 118 degrees. For softer metals or harder materials, 135 degrees might be preferred. The jig will have settings or guides for this.
- Insert the Drill Bit: Secure the drill bit in the jig’s holder or collet. Ensure it’s firmly gripped.
- Coolant Application: Make sure coolant is ready to be applied to the grinding wheel or bit as you grind.
- Grinding Process:
- Engage the grinding wheel.
- Bring the jig with the drill bit to the grinding wheel. The jig is designed to guide the bit at the correct angle and to create the proper relief.
- Move the jig back and forth or pivot it as instructed by the jig’s manual to grind the cutting edge.
- Grind one side until a slight burr is felt on the opposite cutting edge, or until the cutting edge looks sharp.
- Flip the bit or adjust the jig to grind the other side.
- Alternate between sides, taking light passes, and dipping the bit (or the jig with the bit) in coolant frequently.
- Chisel Edge Grinding: Many jigs also have a secondary setting or technique to properly grind the chisel edge. This is usually a shallow pass to ensure the two cutting edges meet cleanly at the center.
- Final Check: Remove the bit from the jig. Inspect the point. You should see two sharp, symmetrical cutting edges with a well-formed point. The chisel edge should be minimal.
- Test: Test the sharpened bit on scrap material.
Sharpening Specific Types of Drill Bits
Sharpening HSS Drill Bits
HSS drill bits are common and relatively easy to sharpen. The key is to avoid overheating.
- Grinding Wheel: Standard aluminum oxide wheel.
- Coolant: Essential. Water or a cutting fluid for grinding is highly recommended.
- Technique: Use light passes and frequent cooling. Aim for a consistent 118-degree point angle. You are grinding the clearance angle behind the cutting edge.
Sharpening Carbide Drill Bits
Carbide drill bits are much harder and more brittle than HSS. Sharpening them requires a different approach and wheel.
- Grinding Wheel: Silicon carbide wheel is mandatory. Aluminum oxide wheels will not work effectively and can be damaged.
- Coolant: Crucial to prevent thermal shock, which can crack the carbide.
- Technique: Carbide is harder to grind. You will likely need more passes. Be gentle and very consistent with cooling. The grinding wheel angle and drill point angle are just as important as with HSS bits. A jig is highly recommended for carbide bits to ensure accuracy.
Sharpening Left-Handed Drill Bits
These bits cut in the reverse direction. The sharpening process is similar to right-handed bits, but you’ll be grinding on the opposite side of the flute relative to the rotation direction. The jig will usually have a way to accommodate these.
Sharpening Step Bits
Step bits have multiple cutting diameters. Sharpening them on a bench grinder is difficult and often not recommended unless you have a very specialized jig. It’s usually better to replace a dull step bit.
What is the Correct Drill Point Angle?
The drill point angle is the angle formed by the two cutting edges at the tip of the drill bit.
- 118 degrees: This is the standard angle for most general-purpose drilling in softer metals like aluminum, brass, and mild steel.
- 135 degrees: This angle is preferred for drilling harder metals like stainless steel, as it provides a more acute cutting edge that can penetrate tougher materials more easily. It’s also sometimes used for plastics.
Using the wrong drill point angle can lead to poor performance or even damage to the bit or workpiece.
Achieving the Right Grinding Wheel Angle
While a bench grinder doesn’t have a precise angle setting like a dedicated sharpening machine, you can approximate the correct grinding wheel angle by:
- Visual Estimation: For freehand sharpening, try to visualize the correct angle (59 degrees from the side of the wheel).
- Jig Guides: Most drill bit sharpening jigs have built-in angle guides or stops that ensure the bit is presented to the wheel at the correct angle.
Maintaining Your Sharpened Drill Bits
After sharpening:
- Deburr: Gently remove any burrs left on the bit with a fine sharpening stone for drills or a deburring tool.
- Clean: Wash the bit thoroughly to remove any grinding residue or coolant.
- Inspect: Check the bit for any signs of overheating (discoloration) or damage.
- Store Properly: Keep your sharpened bits organized in a drill bit index to protect them from damage.
Alternatives to Bench Grinding for Drill Bit Sharpening
While a bench grinder is a common tool, other options exist:
- Drill Bit Sharpening Tool (Handheld): Small, often battery-powered or manual tools that use abrasive cones to sharpen bits. These are convenient for quick touch-ups but may not restore a severely dulled bit as effectively as a bench grinder.
- Diamond Sharpening Stones: For extremely hard bits like cobalt or carbide, specialized diamond sharpening stones can be used. This is often a slower process but can achieve excellent results with care. A fine-grit diamond sharpening stone for drills can be used for touch-ups.
- Professional Sharpening Services: For valuable or specialized drill bits, consider sending them to a professional sharpening service. They have specialized machinery for perfect results.
Common Problems and How to Fix Them
| Problem | Cause | Solution |
|---|---|---|
| Overheating/Discoloration | Too much pressure, not enough coolant, fast grinding | Use lighter passes, ensure ample coolant is applied, slow down the grinding motion. |
| Uneven Cutting Edges | Inconsistent angle, poor technique, no jig | Use a drill bit sharpening jig for consistency, focus on holding a steady angle freehand. |
| Blunt Chisel Edge | Not grinding the center edge properly | Follow the specific instructions for re-sharpening drill bits to grind the chisel edge at a slight angle. |
| Excessive Relief Angle | Grinding too deep behind the cutting edge | Take lighter passes, focus on creating a narrow bevel behind the cutting edge. |
| Wheel Glazing | Overheating, grinding soft materials | Use coolant, slow down, and consider dressing the wheel if it becomes loaded. |
Frequently Asked Questions (FAQ)
Q: Can I sharpen twist drill bits on a bench grinder?
A: Yes, twist drill bits are the most common type to sharpen on a bench grinder.
Q: What grit should my bench grinder wheel be for sharpening drill bits?
A: A medium grit (e.g., 60-80) is generally good for removing material. You can follow up with a finer grit if needed for a smoother finish, but for basic sharpening, a medium grit works well.
Q: How often should I sharpen my drill bits?
A: Sharpen them when you notice a decline in performance (slower drilling, more heat, ragged holes). Regular sharpening keeps your tools in optimal condition.
Q: My drill bits are turning blue after sharpening. What happened?
A: This indicates the bit overheated. Overheating ruins the temper of the HSS steel, making it softer and less able to hold an edge. Always use coolant and light passes.
Q: Is it worth sharpening small drill bits?
A: For very small bits (under 1/8 inch or 3mm), it can be challenging to get accurate results due to their size. Sometimes, replacing them is more practical, but with a good jig and steady hands, it’s still possible.
Q: What kind of coolant should I use for grinding?
A: Water can work in a pinch, but dedicated cutting fluid for grinding is better. It provides lubrication, cooling, and helps prevent rust.
By following these guidelines, you can effectively re-sharpen drill bits on your bench grinder, extending their life and improving your drilling capabilities. Remember to prioritize safety and practice to achieve the best results.