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The short answer
The best grinding wheel for sharpening drill bits on a typical bench grinder is a properly rated, 6- or 8-inch aluminum oxide wheel in 60 grit and medium hardness; choose silicon carbide for carbide bits, and use a diamond wheel when you need to sharpen carbide accurately or often. Check the grinder’s manual and the wheel’s speed rating before buying: diameter, arbor size, thickness, and maximum RPM must all match.
For most home workshops, a 60-grit aluminum oxide wheel is the most useful general-purpose choice for high-speed steel (HSS) and cobalt bits. A 36-grit wheel removes material faster but leaves a rougher finish and makes it easier to overheat a cutting edge. An 80-grit wheel gives more control for light touch-ups, but may sharpen slowly if the bit is badly damaged.
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What to buy for your bits and grinder
| Situation | Abrasive and grit | Common wheel size | Why it fits |
|---|---|---|---|
| HSS bits, occasional sharpening | Aluminum oxide, 60 grit | 6 in × ¾ in × ½ in arbor | A versatile balance of cutting speed and control for many small bench grinders. |
| Cobalt HSS bits, frequent sharpening | Aluminum oxide, 60 or 80 grit | 8 in × 1 in × ⅝ in arbor | Common on larger grinders; the finer option can make light corrections easier. |
| Carbide bits, occasional sharpening | Silicon carbide, 60 grit | 6 or 8 in; match grinder dimensions | Hard abrasive suited to carbide, though a standard grinder setup takes practice. |
| Carbide bits, frequent or precise work | Diamond, typically fine to medium | Wheel or attachment specified for the machine | Efficient on carbide; verify mounting, speed limits, and whether the setup is intended for drill-point geometry. |
| Large, badly chipped HSS bit | Aluminum oxide, 36 or 46 grit | Match the grinder | Faster stock removal, followed by a finer wheel or careful edge finishing. |
These are common sizes, not universal standards. A 6-inch grinder often takes a ¾-inch-thick wheel with a ½-inch arbor; an 8-inch grinder commonly uses a 1-inch-thick wheel with a ⅝-inch arbor. Measure the existing wheel and read the grinder label rather than assuming. Never force a wheel onto an arbor or improvise a reducer that the manufacturer does not approve.
How abrasive, grit, and hardness change the result
Abrasive: match the wheel to the bit
Aluminum oxide is the practical default for HSS and cobalt HSS drill bits. It is widely available in standard bench-grinder sizes and is suitable for routine edge maintenance. Cobalt bits are still a form of high-speed steel; they benefit from controlled grinding and cooling just as ordinary HSS does.
Silicon carbide is harder and is commonly used for grinding carbide. It can also be used on some nonferrous materials, but that does not make it the best general-purpose wheel for every bit. Diamond is especially effective on carbide, but wheel compatibility, bond, speed, and intended use matter. A general-purpose diamond wheel is not automatically the right tool for accurately restoring a drill’s point angles.
Grit: choose between speed and control
Coarse grit—often 36 or 46—cuts quickly and is useful for removing a nick or establishing a new point. It also takes off material quickly, so a small error can shorten the bit or distort its cutting lips. Medium grit, commonly 60, suits most routine sharpening. Fine grit, such as 80 or 100, removes less material per pass and can help with small corrections, but it is not a shortcut for fixing a badly damaged point.
Hardness: wheel grade is not the same as abrasive hardness
Wheel grade describes how strongly the bond holds abrasive grains, not how hard the abrasive itself is. A wheel that is too hard for the task can glaze: its grains dull but remain attached, so it rubs and heats instead of cutting cleanly. A softer grade releases worn grains sooner and exposes fresh cutting edges. Follow the wheel maker’s recommendations for the material, and dress a glazed wheel with a suitable wheel dresser. Do not choose a grade based only on a letter or assume “harder wheel” means better performance.
Choose by workspace and sharpening frequency
| Your situation | Practical choice | Trade-off |
|---|---|---|
| Limited budget, mostly small HSS bits | One 60-grit aluminum oxide wheel that fits your grinder | Good general coverage; less efficient for major damage or carbide. |
| New to sharpening | 60- or 80-grit aluminum oxide; use a drill-bit sharpening guide if needed | More forgiving for small corrections than a coarse wheel, but still requires controlled technique. |
| Frequent workshop use, room for two wheels | 36- or 46-grit aluminum oxide for repair, plus 60- or 80-grit for routine work | Faster repair and more controlled touch-ups, at the cost of a second wheel and more setup space. |
| Mostly carbide bits | Compatible silicon-carbide or diamond setup intended for the task | Better abrasive match, but confirm the machine, wheel, and sharpening method can produce the required geometry. |
If you have only one standard bench grinder and mostly use general-purpose HSS bits, start with a 60-grit aluminum oxide wheel. Buying a coarse and fine wheel is worthwhile when you regularly repair damaged bits and also want a separate wheel for lighter sharpening.
Fit the wheel safely before sharpening
- Match all dimensions: Check diameter, thickness, and arbor size against the grinder and wheel specifications. A smaller wheel may change clearance and grinder behavior; do not install a larger wheel than the machine allows.
- Check the speed rating: The wheel’s maximum RPM must be at least the grinder’s operating RPM. Never run a wheel above its marked limit.
- Inspect and mount: Do not use a cracked, dropped, or damaged wheel. Use the specified flanges and blotters, and tighten only as directed. If the wheel requires a ring test, follow its maker’s instructions.
- Set the tool rest: Keep it close to the wheel—commonly no more than ⅛ inch, subject to the grinder and wheel instructions—and secure the guard. Recheck the gap as the wheel wears.
- True and dress as needed: A wheel that is uneven or glazed makes it harder to hold a consistent drill angle. Dress it with the appropriate dresser; dressing restores a useful cutting surface but consumes some wheel.
Sharpen without burning or shortening the bit
Hold the bit securely and make light, brief contacts rather than pressing hard. Excess pressure can overheat the cutting edge, especially on small bits. Dip the bit in water between passes when appropriate, but do not quench a hot bit in a way that risks thermal shock or splashing; follow safe shop practice and the bit maker’s guidance. A straw-colored or blue tint can indicate heat damage to the edge.
Keep both cutting lips symmetrical and preserve the point angle appropriate to the work. A standard general-purpose twist drill commonly has a 118-degree point; some applications use 135 degrees. A wheel choice alone will not restore the correct geometry. A guide or dedicated drill-bit sharpener can help maintain the angle and lip balance, especially for beginners.
Ownership realities: wear, maintenance, and common mistakes
Grinding wheels wear down in diameter, and dressing removes additional material. A smaller wheel can affect clearance and the grinder’s effective surface speed, so replace it when it reaches the grinder or wheel maker’s minimum size—not merely when it looks old. Store wheels dry and handle them carefully; impact damage can make a wheel unsafe even when a crack is hard to see.
The most common buying mistakes are choosing by grit alone, overlooking arbor and thickness, and confusing wheel grade with abrasive type. The most common sharpening mistakes are pressing too hard, holding the bit in one spot until it heats, and changing one cutting lip more than the other. For a typical home bench grinder, a correctly sized 60-grit aluminum oxide wheel remains the sensible first choice for HSS and cobalt bits; add a carbide-specific wheel only when your bit material and sharpening workload justify it.