How to Tell If a Drill Bit Needs Sharpening (And What to Do About It)

A dull drill bit doesn't announce itself. It just gets worse — slower feed, more heat, rougher holes, broken taps downstream. Most shops run bits well past the point where a regrind would have saved time and money. Learning to catch it early changes that.

1. THE BIT IS SQUEALING OR CHATTERING

A sharp drill is quiet for its size. Feed pressure is steady. The cutting action feels clean. When a bit starts to squeal — a high-pitched continuous sound during the cut — that's the worn flank rubbing against the workpiece rather than shearing through it. Chatter (an intermittent vibration and noise) follows from the same cause: the edge isn't cutting, it's bouncing.

You'll hear it before you measure it. Trust the sound.

2. HEAT AND SMOKE FROM THE HOLE

A sharp bit cuts and evacuates chips efficiently. A dull bit generates heat through rubbing. If you're seeing smoke from the hole, blue chips coming out on steel, or the workpiece is hot to the touch near the hole — the bit is dull. The heat is going into the material (and into the bit), accelerating edge wear and potentially hardening the zone ahead of the drill through work-hardening.

3. THE BIT REQUIRES MORE PRESSURE THAN NORMAL

If you're leaning harder than usual on the quill, adding more power on a drill press, or adjusting feed downward on a CNC to get the bit through — it's dull. A sharp bit feeds willingly at the correct rate. A dull bit requires more force to do the same thing and produces worse results doing it.

4. HOLE QUALITY HAS CHANGED

Oversized holes, rough sidewalls, bell-mouth entry (where the hole is larger at the top than the bottom), or holes that wander off-center — all are symptoms of dullness, especially asymmetric dullness where one lip has worn more than the other. If your holes used to come in clean and they don't anymore with the same setup, check the bit before checking the machine.

5. VISUAL INSPECTION: THE POINT TELLS YOU

Look at the drill point under a loupe or 10x lens. A sharp HSS bit has crisp, defined cutting lips with a consistent bevel. A dull bit shows a rounded or flat land at the lip edge — the thin shiny stripe where the material has been worn away. Under magnification, this is unmistakable. A new shop practice: look at one or two bits a week under magnification so you know what sharp looks like and recognize dull immediately.

WHAT TO DO WHEN YOU SPOT IT

Pull the bit and set it aside for resharpening. Running a dull bit longer doesn't save money — it accelerates wear on the cutting edge (making the regrind remove more material), damages the workpiece, risks broken taps, and builds bad habits. The bit gets pulled eventually. Better to pull it at the first sign than after a scrapped part.

For mail-in resharpening, collect your worn bits into a bin and ship when you have a useful quantity. MachinistPost handles individual bits up through full shop orders — the per-bit cost is the same regardless of quantity.

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