Technical Foundation
What Is a Keyway Broache?
A keyway broach is a hardened, tapered-tooth cutting tool pushed or pulled through a pre-bored hole to cut a straight internal keyway slot, sized to the width of the key that will transmit torque between a shaft and a hub, gear or pulley. Push-type broaches are the standard shop method — driven through the bore under an arbor press using a guide bushing sized to the bore diameter, with the broach's teeth progressively deepening the cut across multiple passes.
Shims are inserted behind the broach between passes to advance depth incrementally rather than removing all material in one pass, which would overload the teeth and risk breakage; a typical broach kit includes a set of shims sized to cut standard keyway depths per ANSI B17.1. The guide bushing, sized to the specific bore diameter, keeps the broach aligned through the cut and is a separate purchase matched to both the broach width and the bore.
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| Spec | What It Means | Why It Matters |
|---|---|---|
| Keyway Width | Sized to standard key sizes (1/8 in to 1 in, or metric) | Must match the key that will be installed per ANSI B17.1 or equivalent metric standard |
| Broach Style | Push-type (arbor press) vs. pull-type | Push-type with a guide bushing is the standard shop method for internal keyways |
| Bushing Bore Size | Matched to the workpiece bore diameter | Guides the broach straight through the cut — incorrect bushing size allows the broach to wander |
| Shim Set | Incremental thickness shims per pass | Advances cutting depth gradually across multiple passes to avoid overloading the broach teeth |
| Broach Length | Sized to bore depth plus overtravel | Must be long enough to fully clear the workpiece on each pass without running out of travel |
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Applications
Where Keyway Broaches Get Used
Keyway broaches are specified wherever an internal keyway must be cut into a bore to accept a key transmitting torque between a shaft and a hub.
Power Transmission & Gearbox Repair
Cutting new internal keyways in replacement gears, sprockets and couplings to match shaft key sizes.
Machine Shop & Custom Fabrication
Broaching keyways into pulleys and hubs during custom shaft-and-hub assembly work.
Motor & Pump Repair
Restoring or resizing keyways in motor couplings and pump impeller hubs during rebuild work.
Agricultural Equipment Maintenance
Field and shop repair of worn or damaged keyways in PTO shaft components and implement hubs.
Tool & Die Manufacturing
Precision keyway cutting in fixture and jig components requiring accurate torque-transmitting slots.
FAQ
Keyway Broaches Questions, Answered
How do I determine what keyway broach size I need?
Match the broach width to the key size required by the shaft and hub design, per ANSI B17.1 (or the applicable metric standard) — key size is typically specified relative to shaft diameter on the drawing or by the original equipment's key. The broach's bushing must separately match the bore diameter of the part being broached.
What's the guide bushing for, and do I need to buy it separately?
The bushing sits in the bore and guides the broach straight through the cut, preventing it from wandering off-center; it's sized to the specific bore diameter and is typically a separate purchase from the broach itself, since one broach width can be used across multiple bore sizes with different matched bushings.
Why do keyway broach kits come with shims?
Shims are inserted behind the broach between passes to progressively increase cutting depth in controlled increments — pushing a broach through in a single full-depth pass overloads the teeth and risks chipping or breaking the broach. A shim set lets you reach full keyway depth (per ANSI B17.1) across several manageable passes.
Can I use a push-type broach without an arbor press?
No — push-type keyway broaching requires an arbor press (or hydraulic press) to provide the controlled, straight-line force needed to drive the broach through the bore. Attempting it without a press risks an uneven or misaligned cut and excessive tool wear.
What's the difference between a keyway broach and a Woodruff keyway cutter?
A keyway broach cuts a straight, uniform-depth internal slot for a standard rectangular or square key. A Woodruff keyway cutter is a rotary milling cutter used to cut the curved-bottom seat for a semicircular Woodruff key, typically on a shaft rather than a bore, and uses entirely different tooling and setup.
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