Internal Broaching

Internal broaching cuts keyways, splines, and internal profiles through a pre-drilled hole in one stroke, delivering fast cycle times and consistent geometry.

Overview

Internal broaching forms internal keyways, splines, and other non-round profiles by pulling or pushing a multi-tooth broach through a starter hole. Each tooth removes a small amount of material, so the feature is generated in one pass with good repeatability and high throughput once tooled.

Choose it for production parts needing consistent internal drive features—especially in steels—where cycle time matters and the profile is standardized. Tradeoffs: you need a through-hole (most common) and enough clearance for the broach to enter/exit; blind features are possible but more specialized. Tooling is feature-specific, so setup cost is higher than single-point machining but amortizes well over volume. Broaching can leave a characteristic surface finish and requires attention to burr control at entry/exit.

Common Materials

  • 4140 steel
  • 8620 steel
  • AISI 1018
  • Aluminum 6061
  • Brass 360
  • Stainless 304

Tolerances

±0.001" to ±0.003"

Applications

  • Internal keyways in gears
  • Spline hubs for power transmission
  • Pulley hubs with keyways
  • Couplings with internal splines
  • Automotive transmission components
  • Hydraulic pump drive hubs

When to Choose Internal Broaching

Internal broaching fits parts that need repeatable internal keyways or splines at medium to high volumes, with a pre-machined pilot hole and straight-line tool access. It’s a strong choice when you want the feature completed in one pass with predictable cycle time and minimal operator variability.

vs Surface Broaching

Choose internal broaching when the functional geometry is inside a hole—keyways, splines, or internal forms—and you can provide a starter bore for tool guidance. Surface broaching targets external flats, slots, and contours on accessible faces; internal broaching is optimized for internal drive features with straight-through access.

vs CNC milling (keyway cutting)

Choose internal broaching when you need faster per-part cycle time and tighter feature-to-feature repeatability across a run. CNC milling works well for low volumes and nonstandard geometries, but it’s typically slower per feature and more sensitive to tool wear and programming strategy.

vs Wire EDM

Choose internal broaching when material removal speed and piece-part cost matter and the profile is a standard keyway/spline. Wire EDM handles very hard materials and intricate profiles with sharp internal corners, but it’s usually slower and costlier per part for production quantities.

vs Shaping / slotting

Choose internal broaching when you want the keyway or spline completed in one pass with consistent geometry. Shaping/slotting can cut internal features without dedicated broach tooling, but it’s generally slower and more variable from part to part.

Design Considerations

  • Specify whether the feature is through or blind and provide the available broach runout/exit clearance
  • Call out the pilot hole diameter, tolerance, and surface finish needed for broach guidance
  • Avoid interrupted cuts, cross-holes, or thin walls intersecting the broached profile near the cutting zone
  • Plan for burrs at entry/exit; define deburr requirements and any protected sealing surfaces
  • Use standard keyway and spline standards (ANSI/ISO/DIN) to reduce tooling cost and lead time
  • Define datum relationships and allowable runout/concentricity between the broached profile and the bore/OD