How to Inspect a Drill Bit Before Using It: A 60-Second Pre-Flight

Most machinists grab a drill bit out of the rack and put it in the chuck. The bit might be sharp. It might be dull. It might have a hairline crack from the last time someone bent it sideways. You won't know unless you look.

A 60-second inspection before every drill catches the problems that scrap parts, break bits mid-hole, and turn a five-minute drilling job into an extraction operation. Here's the routine, checkpoint by checkpoint.

1. The Shank

Start at the shank — the smooth section that enters the chuck or collet. Look for:

Shank Damage

Flat spots, gouges, or chuck bite marks on the shank cause runout. If the shank isn't round and concentric, the bit won't run true no matter how well the chuck is tightened. Light surface marks are acceptable. Significant gouges or flat spots from a loose chuck are not — the bit will wobble, the hole will be oversize, and the bit will wear faster. Retire it or regrind it down to a clean section of shank.

Shank Diameter

Drills lose diameter when reground improperly or when the shank section is accidentally reduced. If a drill is marked 1/2" but the shank measures undersized on a micrometer, it was reground incorrectly. This causes it to slip in the chuck under load — especially on breakthrough, which is exactly when you don't want it spinning freely.

2. The Body and Flutes

Hold the drill at eye level and rotate it slowly. The body should appear straight. Flex in a drill body — even slight visible curvature — means the steel was bent, possibly from a previous bind or crash. A bent drill will produce oversized, off-center holes and is a candidate for snapping under load. Don't run a bent drill.

Flute Condition

The flutes spiral from the tip toward the shank. They should be clean, unobstructed, and free of cracks. Check for:

• Cracks running across the flute: These are stress fractures and mean the bit is ready to break. Discard immediately.
• Chip packing: Dried chips welded in the flute from a previous job with inadequate coolant or insufficient pecking. This reduces chip clearance and can cause the bit to bind. Clean with a wire brush before using.
• Corrosion: Light surface oxidation on the body is cosmetic. Rust pitting inside the flute that reduces depth is a structural concern for smaller-diameter drills — the cross-section at the pitted area is weaker.

3. The Point Geometry

This is the most important part of the inspection and the part most machinists skip. Hold the drill under good light and look directly at the tip.

Lip Symmetry

Both cutting lips — the two main cutting edges — should be the same length and the same angle. Sight down the drill axis and compare them. Any visible difference in length means one lip will cut more than the other on every revolution. This is the primary cause of oversized holes. A drill that should cut 3/8" will consistently run 0.005–0.015" oversize with mismatched lips.

Chisel Edge Width

The chisel edge is the short flat section at the very center of the point, bridging the two lips. On a fresh or properly resharpened bit, it's narrow and sharp. On a worn bit, it's wide and flat from being rubbed against the workpiece. A wide chisel edge dramatically increases drilling thrust — the force required to advance the drill. If you're leaning hard on the feed and the bit isn't advancing, feel the chisel first.

Lip Relief

Behind each cutting lip, the face should slope away — this is the lip relief angle. It's what allows the cutting edge to bite rather than rub. Without adequate relief, the edge rides on the workpiece without cutting, generating heat and accelerating wear. You can check this visually: the face behind the lip should be clearly angled away, not flat. A flat or negative relief angle means the bit needs a regrind.

Blue Discoloration at the Tip

Blueing at the cutting edges is a heat warning. It means the bit was run fast enough to draw the temper — the steel's heat treatment — at the cutting zone. A bit that has been run blue at the tip has softer edges than a properly maintained bit, regardless of how the geometry looks. Blue discoloration running up the flutes or toward the shank is worse and suggests the steel was overheated significantly. Discard or mark for regrind — but understand that regrinding may remove the blued material without restoring full hardness if the damage runs deep.

4. The Go / No-Go Decision

After the inspection, you're making one of three calls:

1. Run it. Shank is clean, body is straight, lips are symmetric and sharp, chisel edge is narrow, relief is present. Use it.
2. Regrind it. Worn chisel edge, dull lips, lost relief, or unequal lip height — these are all geometry problems fixable with a proper machine regrind. Don't use it on a precision job in this condition; set it aside for resharpening.
3. Retire it. Cracks in the flute, bent body, heat damage running up the shank, or a bit so short from previous regrinds that the remaining flute length is insufficient to evacuate chips. Replace it.

The 60 seconds spent on this inspection is the cheapest insurance in the shop. It costs nothing. It prevents scrapped parts, broken extractors, and lost production time.

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