The round-hole broach is the simplest of the internal broaches. It produces close-tolerance parts and smooth surface finishes in high-production applications.

The round-hole broach has a series of teeth that fully encircle the tool. Each tooth cuts on its entire outer edge.

When broaching ductile materials, round-hole broaches that incorporate chipbreakers are recommended. They effectively break the stringy chips that form. 

A variety of hole shapes can be broached besides round ones. Internal broaches cut square, rectangular, octagonal, and hexagonal holes, as well as any other internal shape. All that's required is the proper starting hole for inserting the tool. One of the most common internal broaches is the keyway broach, which resembles a slot broach. A fixture called a "horn" usually supports the broach, locating the part in the hole where the keyway is to be cut.

To cut internal gear forms, and internal gear broach is used. Its tooth pattern gradually "nibbles" away at the work piece’s internal surface, generating the desired gear profile. A full-form finishing broach may be needed to ensure accuracy and provide the optimum surface finish. 

Broaching gun-barrel bores necessitates a rifling broach. This special tool is very long so it can traverse the barrel’s full length. It has relatively few teeth, as barrel grooves are only a few thousandths of an inch deep. The broaching machine pulls the broach through the bore while simultaneously rotating it to produce the spiral pattern 

In some spline-broaching applications the pitch diameter must be precisely concentric with the part’s minor diameter. A concentricity broach ensures this because it has a full-form finishing section possessing alternating round and spline teeth that shave the minor diameter and spline form.

Cutting splines in thin-walled parts can be a problem. During the operation, the walls expand with the broach’s passage, but then spring back, leaving improperly cut splines. A cut- and- recut- broach solves the problem. It has a "breathing area" behind the front cutting section that prevents part shrinkage. The front of the tool cuts the spline, then another cutting section at the broach’s end re-cuts it to precise tolerances. 

Horizontal vs. Vertical Machines 

The two most important factors to consider when selecting a broaching machine are the type of broach required for the application and the number of parts to be produced. Machine size is determined by broach length. How much force will be exerted on the tool, whether it’s a push-or pull-broaching operation, and available floor space. 

Horizontal machines are utilized primarily for pull-through applications. One-way (cutting in one direction) and two-way (cutting in both directions) models are available. 

The automotive industry makes extensive use of large horizontal surface broaching machines to remove heavy amounts of stock. These machines cut surfaces on large parts like cast engine blocks, cylinder heads, manifolds, and bearing clusters. With carbide insert, stock-removal rates of ¼" or more are possible. 

Formerly, most broaching was done on horizontal machines. But today they represent just 10 percent of all the broaching machines purchased. Vertical broaching machines have become more popular because they take up less space. This is an important consideration in plants where floor space is at a premium. 

A drawback to vertical machines, though, is that they require a higher ceiling than horizontal models. The plants with low ceiling, horizontal machines still are used, and they also find use as special, low-profile equipment for transfer lines and short-run applications. 

Vertical machines typically are used for surface broaching. In operation, either the broach tool passes over the work piece or remains stationary while the part moves. 

< Page 1 | Home | Page 3 >