Broaching

Broaching forms precise internal or surface profiles in one pass using a toothed tool, delivering fast cycle times and consistent accuracy at production volumes.

Overview

Broaching cuts a profile by pulling or pushing a multi-tooth tool (broach) through or across the workpiece. Each tooth removes a small amount of material, so a full form—keyway, spline, hex, or flat—finishes in a single stroke. Common variants include internal broaching (through holes) and surface broaching (external flats, slots, and contours).

Choose broaching when you need repeatable formed features at medium to high volumes, especially internal shapes that are slow to mill. The main tradeoffs are tooling cost/lead time and feature constraints: you need a clear broach path, stable fixturing, and typically a through-feature for internal broaching. Broaching excels on ferrous alloys and many aluminums, but very hard materials may require specialized tooling or alternate processes. Expect excellent consistency and low unit cost once tooled, with less flexibility for late design changes.

Common Materials

  • Steel 1018
  • Steel 4140
  • Stainless Steel 303
  • Aluminum 6061
  • Bronze 932

Tolerances

±0.001" to ±0.003"

Applications

  • Internal keyways in hubs and gears
  • Involute and straight splines in couplings
  • Hex and square drive holes in fittings
  • Automotive transmission components
  • Pump and valve internal profiles
  • Surface flats on shafts for wrenching

When to Choose Broaching

Broaching fits parts that need a specific formed profile repeated many times, where cycle time and part-to-part consistency matter. It’s strongest for internal features like keyways, splines, and polygons, and for external flats/slots when a straight tool path is available. Plan for dedicated tooling and stable volumes to amortize setup and broach costs.

vs Milling

Choose broaching when the feature is a standard repeated profile (keyway, spline, hex) and you want one-stroke cycle time with minimal interpolation error. Milling is better for low volumes and frequent design changes; broaching wins once quantities justify tooling and you have a clear linear tool path.

vs Turning

Choose broaching when the critical feature is non-round (internal spline/hex/keyway) that would otherwise require secondary ops after turning. Turning is ideal for rotational geometry; broaching efficiently adds the formed profile with high repeatability once the turned blank is ready.

vs Drilling

Choose broaching when a hole needs a shaped form (square, hex, spline, keyway) beyond a simple round bore. Drilling creates the pilot/through hole efficiently; broaching then forms the final profile accurately and consistently in production.

vs Grinding

Choose broaching when you need a formed profile quickly and can hit requirements without a ground finish. Grinding is the better choice for very tight tolerances, exceptional surface finish, or hardened parts where a broach would wear quickly.

vs Electrical Discharge Machining (EDM)

Choose broaching for high-throughput production of common profiles in machinable materials, where per-part cost must be low. EDM handles very hard materials and intricate shapes with no cutting forces, but typically has slower cycle times and higher per-part cost for production quantities.

Design Considerations

  • Design internal broached features as through-features with a relief/exit so the broach can pass completely through
  • Provide a properly sized pilot hole/bore and specify whether the shop supplies it or you do (it drives broach selection)
  • Use standard profile sizes (keyway widths, spline standards, hex across-flats) to avoid custom broach tooling
  • Add lead-in chamfers and specify burr direction/allowable edge break to control assembly issues
  • Avoid interrupted cuts or cross-holes along the broach path unless the shop confirms it’s acceptable for tool life and finish
  • Call out datum surfaces and functional tolerances (fit, runout to bore/OD) so fixturing and inspection match assembly needs