Surface Broaching

Surface broaching cuts external flats, serrations, and profiles in a single stroke using a progressive-tooth broach, delivering fast cycle times at production volumes.

Overview

Surface broaching (external broaching) machines external features by pulling or pushing a multi-tooth broach across a part’s surface. Each successive tooth removes a small amount of material, so the final profile—flats, splines/serrations, keyways, grooves, or form surfaces—comes off complete in one pass with consistent geometry.

Choose it for medium to high volumes where a repeatable external feature drives function and inspection: fast cycles, stable dimensions, and low operator dependence once fixtured. Tradeoffs center on broach and fixture cost, lead time, and process flexibility; the profile is “locked in” to the tool, so design changes get expensive. Parts also need solid locating surfaces and a clear broach path; interrupted cuts, heavy scale, or large stock removal can shorten tool life and hurt finish.

Common Materials

  • AISI 1045
  • AISI 4140
  • AISI 8620
  • 17-4 PH stainless
  • Aluminum 6061
  • Brass C360

Tolerances

±0.001" to ±0.003"

Applications

  • External keyways on shafts
  • Wrench flats on fittings and valve stems
  • External serrations on shift/actuator shafts
  • Dovetail or rail profiles on slides
  • Locking notches and index profiles on levers
  • External spline-like drive features on couplers

When to Choose Surface Broaching

Surface broaching fits parts that need an accurate, repeatable external profile produced quickly after you’ve frozen the design. It’s most economical at medium to high volumes or for families of parts that share the same broached feature. Plan on dedicated fixturing and a straight, obstruction-free tool path across the broached surface.

vs Internal Broaching

Choose surface broaching when the critical feature is external—flats, external serrations, external keyways, or open-faced forms—so the broach can traverse the outside surface with simple loading and robust fixturing. Internal broaching is better when the feature must be contained in a bore (internal spline/keyway) and requires an internal pilot/guide.

vs CNC Milling

Choose surface broaching when the same external profile repeats across many parts and cycle time consistency matters; one broach stroke can replace multiple milling passes and tool changes. Milling is more flexible for frequent design changes, variable geometry, or low volumes where broach tooling can’t amortize.

vs Shaping/Slotting

Choose surface broaching when you need higher throughput and tighter part-to-part consistency on an external form. Shaping/slotting can be cost-effective for very low volumes or long strokes, but it’s typically slower and more sensitive to operator/setup variability.

vs Grinding (Form/Surface)

Choose surface broaching when you need to generate the form efficiently from solid material with good dimensional control but don’t require grinding-level finish or micron tolerances. Grinding is the pick for hardened materials, very fine finishes, or tight geometry control where broach cutting forces or tool wear would be limiting.

Design Considerations

  • Provide a straight, unobstructed broach travel path and specify where the tool enters/exits the cut
  • Define solid locating datums and clamping faces; broaching accuracy depends heavily on fixturing rigidity
  • Limit stock allowance to a realistic broach depth per tooth; avoid asking the broach to remove large amounts in one pass
  • Call out surface finish and edge break requirements; broaching can leave exit burrs that may need secondary deburr
  • Avoid interrupted surfaces (holes, slots, cross-drilled features) in the broach path unless the shop confirms tool life impact
  • Document feature tolerances and datum scheme clearly; profile tolerances without a datum strategy drive fixture complexity and cost