Broaching

Keyways. Splines.
Square holes.
Fast & precise.

Broaching cuts complex internal features in a single pass with a multi-tooth tool — keyways, splines, square and hex holes, gear teeth. Fast for production, holds tight tolerance, produces complex profiles other processes cannot.

Broaching Quote CNC milling

±0.025 mm Single pass Complex profiles 6–100 mm bore

01 · What it is

How Broaching works.

Broaching is a metal-cutting process that uses a multi-tooth tool (broach) to cut a specific profile through a workpiece in a single linear pass. Each tooth of the broach is slightly larger than the previous one, so each tooth removes a small amount of material progressively deeper into the cut. The result: complex internal profiles cut to final dimension in one stroke.

Linear broaching pulls or pushes the broach through a pre-drilled hole, cutting internal features like keyways, internal splines, square holes, and hex holes. Rotary broaching (polygon turning) uses a rotating broach tool on a lathe to cut external polygonal features like hex heads, square heads, and Torx recesses.

Broaching wins where other processes struggle: complex internal geometry impossible with end mills, production speed (single pass per feature), and excellent surface finish (Ra 0.8 µm typical). Primary limitation: each broach is geometry-specific, so custom profiles require custom tooling ($500–3000+ per broach design).

02 · Specifications

Capability specs.

±0.025 mm

Tolerance

Standard broaching tolerance on production work. Tighter achievable with precision broaches

Ra 0.8 µm

Surface finish

Single-pass finish. Better than milling, comparable to precision grinding

Single pass

Cycle time

Typical keyway: 5–10 seconds per part. Fastest production process for these features

6–100 mm

Bore size

Internal broaching bore range. Smaller via micro-broach specialty

Any metal

Material

Steel, stainless, aluminum, brass, Inconel, titanium — any machinable metal

$500–3000

Custom broach cost

Tooling investment for non-standard profiles. Amortizes over production volume

AGMA 8

Gear quality

Spline broaching achieves AGMA class 8 gear tooth quality routinely

Polygon turning

Rotary broach

Hex, square, Torx external features — rotary broaching on CNC lathe

03 · Applications

Where Broaching excels.

Internal keyways

Standard keyways in pulleys, gears, sprockets — single-pass broaching

Internal splines

Involute splines and parallel splines for drive shafts, gear connections

Square holes

Square internal holes for drive features, shaft couplings

Hex holes

Internal hex patterns for fastener recesses, drive connections

Gear teeth

Internal gear teeth in ring gears, planetary gear internal teeth

External hex/square

Rotary broached external hex heads on shafts — socket head fasteners

Torx external

External Torx drive features on fasteners — T-series sizes

Automotive drivetrain

Splined shafts, coupling hubs, drive connections in transmissions

Power transmission

Keyed pulleys, splined gears, sprockets with internal drive features

04 · When not to use it

Not suitable for:

Every process has its limits. Being honest about where Broaching isn\'t the right answer saves time and money.

Unique/one-off geometry — custom broach cost unjustified for single parts
Simple features already achievable via milling or wire EDM cost-effectively
Very hard materials (>55 HRC) — broach tool life too short
Very small features below 3 mm — specialty micro-broach territory
Parts where broach pull-through would damage other features

FAQ

Broaching questions.

Volume drives the decision. Single part: end mill a keyway (cheaper setup). Medium volume (10–100): wire EDM the keyway (no custom tooling). High volume (100+ pieces): broach the keyway (fastest per part despite tool cost). Broach tool cost ($500–1500 for standard keyway) amortizes over production — per-part cost drops below other processes above ~100 units.

Production broaching: ±0.025 mm standard on keyway widths and depths. Precision broaching (matched broach sets, slower speeds): ±0.01 mm achievable. Broach tooling also wears, so broach sharpness and tool life tracking matters for consistent tolerance. We monitor broach tool condition and replace before tolerance drift.

Yes up to about 45 HRC. Above that, broach tool life becomes uneconomical — tools dull after a few parts. For hardened materials, alternatives: wire EDM (works on any hardness), grinding of keyways (slower but works on hardened), or broach before heat treatment (then heat treat the whole part if distortion acceptable).

Rotary broaching (also called polygon turning or wobble broaching) cuts external polygonal features on a CNC lathe. Spinning broach tool, offset slightly from the workpiece axis, "wobbles" around the part creating polygon shape. Common applications: hex heads on shafts, square heads on custom fasteners, external Torx features. Much faster than milling these features.

Custom broach tooling: 3–6 weeks to design and manufacture (cutting broach teeth in hardened tool steel is specialty work). Standard broach geometries (keyway widths per ANSI B17.1): available as stock tooling, no lead time. For custom projects, design broach early in product development to avoid tooling lead time bottlenecking production.

Production broaching: $0.50–3 per feature cut depending on complexity. Simple keyway at 1000 pieces: <$1 per part. Complex internal spline: $3–5 per part. Amortized tool cost at 5000-part volume: pennies per part. Very cost-effective for production volumes — often cheaper than any alternative for the specified feature.