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Knowledge Center
Broaching Fundamentals
Broaching Process
Glossary of Terms
Knowledge Center FAQ's

What is Broaching?
What are Internal Broaches?
What are External Form Broaches?
What are Blind-Spline Broaches?
What are External "Pot" Broaches?
What is a Broach Tool Designer?
When is a Broach Tool Ready for Sharpening?

What is Broaching?

Broaching is a machining process that pushes or pulls a cutting tool (called a broach) over or through the surface being machined. Broaches are referred to as multiple-point linear-travel cutting tools and are used to produce flat, circular, and even extremely intricate profiles, as seen from a section perpendicular to the tool travel. A broach is a series of single-point tools arranged successively in the axial direction along a tool body or holder. Each sequential tooth varies in size and shape in a manner that allows each tooth to cut a chip of the proper thickness.

The shape and spacing of each broach tooth is determined by the length of the part being broached, the amount of material being removed by each tooth, and tonnage restrictions of the broaching machine. The chip space between each tooth is designed to sufficiently accommodate the volume of chips generated.

The concept of broaching as a legitimate machining process can be traced back to the early 1850s. Early broaching applications were cutting keyways in pulleys and gears. After World War 1, broaching contributed to the rifling of gun barrels. Advances in broaching machines and form grinding during the 1920s and 30s enabled tolerances to be tightened and broaching costs to become competitive with other machining processes. Today, almost every conceivable type of form and material can be broached.

What are Internal Broaches?
Internal broaches are either pushed or pulled through the part. Strength considerations usually limit the tool design.

What are External Form Broaches?

External form broaches are usually carried on a guided ram and mounted in a broach holding fixture. Strength is generally not a major consideration since the cutting force is transferred to the ram at many places along the length of the broach(es).

What are Blind-Spline Broaches?

A whole new era in broaching dawned when General Broach pioneered the blind-spline broaching process. Unlike conventional broaching, blind-spline broaching allows for the machining of blind surfaces—surfaces that are impeded by a flange or protrusion that does not allow a cutting tool to pass completely through or over it.

Blind-spline tools are designed to cut either internal or external forms. Blind-spline tools are mounted on a rotary dial type or linear machine and the tools are kept in sets. Blind spline tools are single-tooth cutting tools, with each successive tool removing a predetermined amount of material until the desired profile is achieved.

The advantages of using blind-spline broaching over more conventional machining processes are:

  • quick and easy size
  • high degree of accuracy
  • extremely high production
  • extremely high production rates (over 10 times faster than shaping or hobbing)

What are External "Pot" Broaches?

While this type of broaching is also external, it is a distinct category from external form broaching because of its unique process. This type of broaching is used when an external form is required. The form can be splines (straight sided, involute, angular), cam, or lobular.

In a pot broaching set up, the part is usually pushed up through an internal 'pot'; a fixture that houses a series of form inserts. Some pots also include a sequence of shave rings that are mounted at the rear of the broach inserts and are used to enhance the form, spacing, and finish of the resultant part.

What is a Broach Tool Designer?

A broach tool designer is a manufacturing engineer who is concerned with the creation and implementation of the broach tools and associated equipment needed to provide the metal working industry with increased manufacturing productivity while, at the same time, reducing manufacturing costs.

Broach tool design is a specialized area of manufacturing engineering which comprises the analysis, planning, design, manufacture, and use of tools, methods, and procedures necessary for manufacturing productivity. In order to perform these duties, the broach tool designer must have a working knowledge of machine shop practices, tool making methods, machine tool design, manufacturing procedures and practices, as well as the more conventional engineering disciplines of planning, designing, engineering graphics and drawing, and cost analysis.

When is a Broach Tool Ready for Sharpening?

There is a general practice which can be altered to suit each particular situation in determining when a broach tool should be pulled for sharpening. The basic spline tooth tends to have a greater corner breakdown than the wear directly along the cutting edge. When a tool has more than the 0.003" to 0.005" corner breakdown, an O. D. or top grind is recommended.

This effectively removes the worn areas. If the broach tool is not sharpened properly and worn areas are not removed, the corners will break down further and wear back prematurely. Since part tolerances are usually limiting, the practice of O.D. or top sharpening must be done cautiously and sparingly.

General Broach has been awarded the Aerospace ISO certification:
AS9100:2009 (Rev. C) & ISO 9001:2008

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