Broach



Broaching is a machining process that is commonly used to cut complex shapes on shafts and in holes when a precise shape is required. A broach is a special tool that has a series of blades that progressively cut deeper and deeper. There are many different sizes and shapes of broaches including ones that cut square holes and splines. One of the many different types of broaches is a linear broach that is used for cutting keyways in holes. It is used so that a circular shaft with a key can be inserted into a hole with a keyway and the shaft will not rotate or spin within the hole. A linear broach is normally used with a broach machine or some sort of press. Broaching is an efficient machining process because it only takes one pass to make a complete cut.

Setup
The first step is to insert the broach bushing into the hole that is having a keyway cut in it. The bushing should just slide into the hole, but it shouldn't be so loose that it will not hold the broach perfectly vertical. In order for the broaching process to be performed a sufficient size hole is required for the broach to enter, and the size of the hole varies with the broach size and type. Broaching is limited to the shape of the broach because each broach is specifically designed to cut a certain shape, and the part being broached must also be straight and have no varying curves.

Performing the Process
Insert the linear broach into the broach bushing and insert the entire part into the arbor press. Apply steady pressure to the press and you bring the handle down on the broach. Cutting oil should also be used to help lubricate the broach so that it slides easier and it also helps clear the chips away so that a higher quality cut it made.

Final Product
The product is just a simple hole with a groove cut out on one side. If a deeper groove is needed, shims can also be added behind the linear broach in the bushing which pushes the cutting blades out further. An advantage of having a keyway is allowing a higher transmission of torque between a moving part and the shaft that it is mounted on. This allows for a stronger piece of equipment and it can reduce or eliminate the need for a set screw to lock the moving part onto its shaft.