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How to Sharpen an End Mill

Guide · Updated October 28, 2026

Most end mill wear is on the corners and end teeth, so a quick end regrind brings a dull HSS or carbide cutter back for slotting and facing. Regrinding the flutes (OD) is a tool and cutter grinder job and makes the cutter smaller. Know which you need before you start.

Mic the new diameter

An OD regrind changes the cutter size. Check it with a mic proved on gage blocks and update your tool table. The free Gage Block Calculator builds the stack.

Step by step

Inspect the wear: Use a loupe: chipped corners and rounded end teeth mean an end regrind; worn OD lands need a flute grind.
Hold the cutter: Use a collet fixture or 5C indexing fixture that indexes each tooth.
Grind primary clearance: About 6–8° on the end teeth with a fine wheel (diamond for carbide, CBN or aluminum oxide for HSS).
Grind secondary clearance: About 15–20° behind the primary so the land stays narrow.
Add gash and dish: Keep a slight dish (1–2° concave) so only the outer corners cut on the face.
Match all teeth: Index each tooth and grind equal amounts so they cut evenly.
Hone and check: Lightly hone burrs, check with a loupe and indicate tooth heights.

Worked example

A 1/2 in 4-flute HSS end mill is chipped 0.010 in back on the corners. Grind 0.012 in off the end teeth: length drops by 0.012 in, so update the tool length offset by −0.012 in. If the OD also needs 0.003 in per side, the new diameter is 0.500 − 2 × 0.003 = 0.494 in; enter 0.494 in (radius 0.247 in) for cutter comp.

Equal teeth matter

If one tooth sits 0.0005 in higher on the end, it takes most of the cut and wears first. Indicate tooth heights on the end and keep them within about 0.0002 in.

Common problems

Rubbing means too little clearance. Chipping means too much clearance or a heavy land. Uneven wear means teeth are not equal. Burned HSS means too heavy a grind or a loaded wheel.

Tips

FAQ

Can you sharpen carbide end mills?

Yes, with a diamond wheel; many shops send them out.

How much clearance on the end teeth?

About 6–8° primary and 15–20° secondary.

Does sharpening change the size?

An end grind changes length; a flute grind changes diameter.

Is it worth it for small cutters?

Usually not under about 1/4 in; replace them.

How do I know it is dull?

Burrs, poor finish, squealing or chipped corners.

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