Special machine tools for side broaching cut on the side of the workpiece

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  How special machine tools for side broaching remove material
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  Horizontal, vertical, and continuous side broaching machines
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  Broach design, materials, and the fixtures that hold the part
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  Where side broaching beats milling, and where it does not
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  Tolerances, inspection, and the failure modes to watch
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  Side broaching against milling and 5-axis cutting

Broaching is a linear cutting process. A bar carrying a row of teeth, each slightly taller than the last, travels past the workpiece once. Every tooth takes a thin chip, and the sum of those chips is the finished profile. Nothing oscillates, nothing retracts, and the shape of the last tooth is the shape of the cut.

Side broaching points that motion at the flank of the part instead of the end. The tool axis runs parallel to the surface being cut, so the teeth engage the side of a shaft, the inner wall of a bore, or the face of a boss. A single stroke completes a profile that would need many passes on a milling machine.

The rise per tooth sets the chip load. A typical side broach climbs 0.02–0.05 mm per tooth on steel and 0.05–0.10 mm on aluminium or brass. Too little rise and the tooth rubs instead of cutting, which work-hardens stainless and burns the edge. Too much rise and the tooth stalls or chips.

Cutting speed stays low by milling standards, usually 3–15 m/min on steel, because the whole tooth row is in the cut at once. The reward is a surface that often lands at Ra 0.8–1.6 μm straight off the tool, with no visible step between passes.

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  One stroke, one profileThe final tooth defines the finished geometry.
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  Rise per tooth0.02–0.05 mm on steel, 0.05–0.10 mm on aluminium.
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  Low speed, high force3–15 m/min, with the full tooth row engaged.

Horizontal machines dominate side work. The ram travels horizontally and the fixture holds the part so the broach passes along its flank. Stroke lengths run from a few hundred millimetres on small keyway machines to several metres on bed-type units. These are the machines most shops picture when they say special machine tools for side broaching.

Vertical machines pull or push the broach downward. They take less floor space and suit short internal profiles, such as a keyway through a hub. The trade-off is that long broaches need a pit or a tall frame, and chip evacuation is worse because gravity drops chips back into the cut.

Continuous broaching uses an endless chain of broach segments. Parts load at one station and unload at another while the chain keeps moving. Cycle time per part drops to seconds, but the tooling is dedicated to one profile. This is a volume process, not a job-shop process.

There is also the pull-down internal type, where the broach is drawn through a bore from below. It holds straightness well on long bores because the tool is in tension rather than compression. A pushed broach can buckle; a pulled one cannot.

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  HorizontalBest general fit for flank and keyway work.
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  VerticalCompact, good for short internal profiles.
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  ContinuousHigh volume, dedicated tooling only.

Broaches are usually HSS, sometimes with a TiN or TiAlN coating to slow flank wear. Powder-metallurgy HSS holds an edge longer on stainless and high-nickel alloys. Carbide is rare on side broaches because the tooth row is long and the tool is expensive to regrind.

The tooth sequence matters more than the material. Roughing teeth take the bulk of the stock, semi-finishing teeth true the profile, and finishing teeth set the final size and finish. A common split on a keyway broach is 60% roughing, 25% semi-finishing, and 15% finishing teeth.

Fixtures must resist the full cutting force in one direction. A side broach pushes the part sideways, so the clamp needs a positive stop behind the workpiece, not just friction. Any flex shows up as taper along the cut. For a 4,000 mm stroke we check fixture deflection before the first part runs.

Regrinding is routine. Each regrind removes a little tooth height, so the finished size shifts. Shops compensate by grinding the face of the teeth and tracking the accumulated stock removal, or by ordering the broach slightly oversize at the start.

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  HSS with coatingTiN or TiAlN for stainless and nickel alloys.
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  Tooth splitRoughing, semi-finishing, and finishing zones.
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  Positive stopsFriction clamps alone let the part walk.

Pick side broaching when the profile is long, straight, and repeated. A splined shaft with 20 teeth, a keyway through a 300 mm hub, or a flat along a rod are all natural fits. One stroke replaces dozens of milling passes, and the surface finish often needs no secondary operation.

Pick it when the geometry has a sharp internal corner. A broach tooth can be ground with a near-square corner. An end mill cannot, because the tool has a radius. If the drawing calls for a square keyway with a 0.2 mm corner, broaching is the practical route.

Do not pick it for one-off work with a loose tolerance. Broach tooling is specific to the profile, and the setup time only pays back across a batch. For a handful of parts at ±0.05 mm, a 3-axis mill with a keyway cutter is cheaper and faster.

Do not pick it for curved or tapered profiles either. Broaching cuts in a straight line. A curved slot, a helical spline, or a tapered flat needs a mill-turn centre or a 5-axis machine. We run 16 simultaneous 5-axis centres for exactly that class of part.

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  Choose broachingLong straight profiles, square corners, batch work.
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  Choose millingCurves, tapers, one-offs, loose tolerances.
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  Choose 5-axisHelical splines and compound-angle faces.

A well-set broaching machine holds ±0.005 mm on profile size and a few micrometres on straightness over a short stroke. The limit is usually the fixture, not the tool. Long strokes accumulate error, so a 4,000 mm cut is checked at three points along its length, not just at the ends.

Chip control decides the surface. A curled chip that packs into the tooth gullet scores the finished wall on the next tooth. Increasing the rise per tooth slightly, or adding a chip breaker, usually clears it. Flood coolant helps on steel but is not always needed on brass.

Tooth wear shows up as a gradual size drift, not a sudden failure. Tracking the finished dimension part to part gives early warning. Once the drift passes half the tolerance band, the broach comes off for regrinding.

Burrs form at the exit end of the cut. They are small on ductile materials and larger on work-hardened stainless. A light chamfer on the drawing, or a deburring pass in a tumbling drum, handles it. We inspect 100% before shipment and can supply reports on request.

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  Size driftTrack part to part; regrind at half tolerance.
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  Chip packingScores the wall; adjust rise or add a breaker.
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  Exit burrsChamfer the drawing or tumble after cutting.