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How to Use a Keyway Broach

Guide · Updated October 28, 2026

A keyway broach cuts an internal keyway in a gear, pulley or hub in a few press strokes. The broach rides in a slotted bushing that fits the bore; shims behind the broach push it deeper on each pass.

Check the keyway

Measure keyway width with gage blocks or pin gages and depth across the bore with inside calipers or a telescoping gage. The free Gage Block Calculator builds the stack for a width check.

Step by step

Pick the tooling: Choose a broach for the key width and a bushing that is a slip fit in the bore.
Check the bore: Bore must be to size, deburred and long enough to support the bushing; chamfer the entry.
Set up in the press: Stand the part square on the press with the bushing and broach through it, and a support with clearance for the broach underneath.
Lubricate: Coat the broach teeth with cutting oil; on steel use a sulfurized oil.
First pass: Push the broach through in one smooth stroke without stopping mid-cut.
Add shims: Clean chips, add the shim the chart calls for behind the broach and push again.
Check depth: Repeat until the key-side depth matches the drawing, then deburr and test-fit the key.

Worked example

Use one formula for the depth target: finished dimension across the bore = bore diameter + hub keyseat depth, measured from the bottom of the keyway straight across to the opposite wall of the bore. For a standard square key, the hub keyseat depth is half the key height (per ANSI B17.1).

Example: a hub for a 1.000 in shaft. The standard key for shafts over 7/8 to 1-1/4 in is 1/4 in square (0.250 in wide × 0.250 in high), so the hub keyseat depth is 0.250 ÷ 2 = 0.125 in. Nominal target = 1.000 + 0.125 = 1.125 in. Now use the real bore: it measures 1.001 in, so the target becomes 1.001 + 0.125 = 1.126 in. Hub keyseat depth tolerance for this size is typically +0.010/−0.000 in, so a reading of 1.126–1.136 in passes. Use a 1/4 in broach and the 1 in bushing; at roughly 0.06 in per pass that means a pass with no shim, then a pass with the first shim. Check with caliper inside jaws or a telescoping gage across the bore after each pass. If the reading is 1.118 in, you are 0.008 in shallow, so take a light shim pass and check again. Your drawing or the key standard you work to wins over these typical numbers.

Drift and chatter

A keyway that wanders usually means the bushing is loose in the bore or the press ram is not square. Use the correct bushing, keep the part flat on the press and push in one continuous stroke. Chatter often points to a dull broach, no oil or a part that is too hard; broaches are for soft or prehardened steel, not fully hardened parts.

Blind bores

A push broach needs to exit the bottom of the bore. For blind holes, use a shaper-type cut on a slotting attachment or cut the keyway on a mill or wire EDM.

Tips

Hub width: cutting a keyway on a mill for shafts.
Edges: deburring and breaking edges.
Bore size: telescoping gages for checking the bore.

FAQ

Can I broach a keyway without an arbor press?

A hydraulic shop press works; a vise or hammer does not give a smooth stroke and risks breaking the broach.

How much does a keyway broach cut per pass?

It depends on the broach; many standard broaches cut about 0.05–0.07 in per pass. Follow the chart supplied with the set.

Do I need shims for every keyway?

For anything deeper than one pass, yes; shims set each successive depth.

Can you broach hardened steel?

No. Broach before heat treat or use EDM for hardened parts.

Which oil for broaching?

A heavy sulfurized cutting oil on steel; a lighter oil or kerosene on aluminum.

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