Pot broaching is considered an external method because it doesn’t push the tool through the entire work-piece to form a hole, but rather alters the outside edges. It is considered the inverse of an internal broach and can only be used on cylindrically shaped work-pieces.
Pot broaches get their name from the hollow fixture that holds the broach tools. It is a pot-like casing with a hole in the middle that holds multiple broaches over the entire length. This process has largely replaced hobbing, which is a milling process that fabricates gears, splines and sprockets.
Pot broaching requires complex tooling and fixtures, meaning it is a rare process, but the main method of manufacturing gears that have external teeth splines cut into their outside edges. They are also able to cut involute and straight splines, as well as external flats and slots. Pot broaching is done on vertical machines and is often an automated process.
This method of broaching gets its name from the fixture where the broaches are mounted inside. The tools are arranged in the hollow holder, which resembles a pot, and the tool assembly passes over the work-piece to all of its external surfaces. The broach is usually held stationary while one or more work-pieces are continuously pushed into the hollow fixture and through the linear broach tools.
These broaching machines have individual formed broach inserts called sticks, multiple ring broaches or a combination of both types. Pot broaching is often used for spiral broaching, where the part is turned continuously through a spiral-shaped tool in order to produce external threading on fasteners like screws. There are three types of broaching tools that have an internal cutting tool configuration-ring, stick or a combination of both.
When single or multiple work-pieces are pulled or pushed through the bore (hole) of the pot broach, which doesn’t ever move, the tools alter their outside diameters. The broach tools must be sized according to the design of the work-piece.