Surface Broaching

Surface broaching removes material with a multi-tooth linear tool to form precise external profiles in one pass, ideal for repeatable production of complex surfaces.

Overview

Surface broaching (external broaching) uses a long, multi-tooth broach pulled or pushed across an exposed surface to generate profiles, steps, and forms in a single stroke. Each tooth removes a small amount of material, building up to the final shape. This delivers consistent profiles, good surface finish, and tight positional control with short cycle times once tooling is in place.

You choose surface broaching when you need high repeatability on external features at medium to very high volumes: splines on shafts, rack teeth, external flats, or complex form surfaces. It excels when the profile is constant along the stroke direction and you can fixture the part rigidly. The main tradeoffs are high upfront tooling cost, long lead time for custom broaches, and limited flexibility if the design changes. It is less suitable for very low volumes, variable-depth 3D surfaces, or parts that cannot provide adequate support and access for the broach stroke length.

Common Materials

  • Aluminum 6061
  • Low-carbon steel 1018
  • Alloy steel 4140 (normalized)
  • Gray cast iron
  • Brass C360

Tolerances

±0.0015" to ±0.003"

Applications

  • External splines on shafts
  • Steering rack teeth and linear gear forms
  • External flats and pads for fixturing or wrenching
  • Dovetail and T-slot slideways on machine components
  • Turbine disk fir-tree or dovetail slots
  • External serrations for press-fit joints

When to Choose Surface Broaching

Use surface broaching when you need a repeatable external profile along a straight path on many identical parts, and can justify custom tooling. It fits best for medium to high production of shafts, racks, and external forms where cycle time and consistency are critical. Parts must allow straight-line tool access and rigid fixturing along the full broach stroke.

vs Internal Broaching

Choose surface broaching when the critical features are accessible from the outside and run along a straight path, such as external splines or flats. Internal broaching is better suited to blind or through-holes where the profile must be formed inside the part geometry.

vs CNC machining

Choose surface broaching when the profile is constant, volumes are high, and cycle time matters more than flexibility. CNC is better when you expect frequent design changes, low volume, or complex 3D surfaces that vary along the tool path.

vs Gear hobbing

Choose surface broaching for linear gear forms like racks or when you need a non-standard external profile in a single pass. Gear hobbing is typically better for standard involute gears on shafts where continuous rotary cutting is more economical.

vs Grinding

Choose surface broaching when you need high throughput forming of external shapes with good but not ultra-precise surface finish. Grinding is a better fit when you need very tight tolerances, superior surface finish, or minor stock removal on hardened parts rather than full-profile generation.

Design Considerations

  • Keep the profile constant along the broach stroke; avoid features that change depth or shape mid-stroke
  • Provide run-in and run-out relief or escape grooves so the broach can enter and exit cleanly without leaving steps or burrs
  • Design fixturing surfaces and datums close to the broached area to minimize deflection and improve dimensional control
  • Avoid very tall, thin walls or unsupported sections along the broached path that can deflect or chip under cutting loads
  • Specify tolerances that match typical broaching capability and reserve grinding only for features that truly need tighter control
  • Share expected annual volume and material condition (hardness, heat treatment state) with the shop so they can size and sequence the broach correctly