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The Fundamentals of Broaches

The Fundamentals of Broaches

Keyway Broach

Square Broach

DEFINITION OF BROACHES

A broach is a bar-shaped cutting tool that contains a series of teeth, which get progressively larger and/or differ in shape from the starting end. Each tooth removes a small amount of material as the tool moves through the workpiece in a one-pass operation. Please note: Broach types correspond to specific bushings i.e. a B-1 broach will need a B-1 Collared Type bushing.

TYPES OF BROACHES

  • Keyway: Slides through a bushing to produce a keyway. Shims are often required to accomplish the desired depth of cut.
  • Square: Have an oversized pilot leaving drill marks in the flats (to provide relief) while establishing four corners. Longer lengths of cut are possible with standard square broaches.
  • Full Square: Leaves no radius in the flats of the broached piece. The pilot diameter will equal the finished square size.
  • Hexagon: Produces hexagonal holes.
  • Production Keyway Construction offers maximum speed and accuracy in production runs of identical bores.
  • Production keyway broaches require no shims or bushings and can cut standard depth of 1/8" to 1/4" keyways in one pass.
  • One-Pass Keyway: Designed for smaller production runs (several hundred) of identical keyways.
  • AF Stock: This is a pull broach featuring a superior tooth design for precision keyway tolerances.

BROACHING OPERATIONS

  • Internal: Shapes around-drilled hole into any configuration. This broaching can be done with either a push or a pull broach. Most broaches are push broaches. Pull broaches (AF Stock) offer longer lengths of cut when broaching square and hexagon shapes. Examples include tooling fixtures, gear and pulley keyways, keyways, rifling and all hole configurations.
  • External (Surface): Used in place of milling or shaping operations because it can produce exact dimensions at a much faster rate. Examples include flats, notches, keyways, contoured surfaces, external gear teeth and serrations.

ACCESSORIES

  • Bushings: A metal slotted liner that supports and guides the broach. Available in Plain or Collared types. Collared bushings are for ease of use in smaller holes.
  • Shims: A thin piece of metal used to achieve a given depth of keyway in a bore.

FACTORS AFFECTING BROACHING

  • Material to be Broached: Materials with hardness up to HRC 38 are best suited for broaching. Harder materials are not recommended.
  • Tool Alignment: Proper tool alignment is necessary to avoid breakage or drifting. To avoid producing a part outside of the required tolerance make sure at least two teeth are engaged at all times and use bushings to support the broach.
  • Lubrication: Proper lubrication reduces friction and helps with chip removal.
  • Chip Removal: Clear chips with a stiff brush from the cutting section of the broach following each pass.
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