The type of broach cutting tool required
for a given job is the single most important factor
in determining the type of broaching machine to
be used. Second in importance is the production
requirement. Taken together, these factors usually
determine the specific type of machine for the job.
The type of broach tool (internal or surface) immediately
narrows down the kinds of machines that could be
used. The number of pieces required per hour, or
over the entire production run, will further narrow
For example, a dual-ram machine with
one operator may be chosen over two single-ram machines
requiring two operators, to provide higher output
per man-hour. The single operator can load one table
of a dual-ram unit while the other ram is cutting.
Even higher production requirements may dictate
a continuous chain horizontal machine. The machine
size in a particular model is a function of the
tool size, workpiece size, broaching power requirements,
and available production space.
For internal broaching, the length
of a broach in relation to its diameter may determine
whether it must be pulled rather than pushed through
the workpiece, for a broach tool is stronger in
tension than in compression. This in turn, helps
determine the type of machine for the job. A short
push broach often is handled in a press instead
of expensive ram-type broaching machine. Presses,
of course, can be converted to pull short broaches
by the addition of a pull-down adapter that converts
push strokes to pull strokes.
Lubrication, workpiece size, chiphandling
characteristics, and surface finish help determine
whether a pull-up or a pull-down broach should be
used. The trend is strongly to pull-down machines
because gravity helps feed lubricant to the cutting
teeth. Large workpieces are more easily handled
in a pull-down than in a pull-up machine.
The type of drive - hydraulic or electro-mechanical
- is another important factor in machine selection.
So are convertibility and automation. Some machine
designs allow for conversion from internal to surface
work, for example. Some designs are fully automated:
others are limited in scope and operate only with
close operator supervision.
Here is a rundown of the major types
of broaching machines:
VERTICAL BROACHING MACHINES
About 60% of the total number of broaching
machines in existence are verticals, almost equally
divided between vertical internals and vertical
surface or combination machines. Vertical broaching
machines, used in every major area of metalworking,
are almost all hydraulicallly driven. One of the
essential features that promoted their development,
however, is beginning to turn into a limitation.
Cutting strokes now in use often exceed existing
factory ceiling clearances. When machines reach
heights of 20 feet or more, expensive pits must
be dug for the machine so that the operator can
work at factory floor level unless they are the
Vertical Internal Broaching
These are either table-up, pull-up, pull-down, or
push-down, depending upon their mode of operation.
Vertical Internal Pull-Up Type
The pull-up type, in which the workpiece is placed
below the work table, was the first to be introduced.
Its principal use is in broaching round and irregular-shaped
holes. Pull-up machines are now furnished with pulling
capacities of 6 to 50 tons, strokes up to 72 in.,
and broaching speeds of 30 fpm. Larger machines
are available; some have electro-mechanical drives
for greater broaching speed and higher productivity.
Vertical Internal Pull-Down
The more sophisticated pull-down machines, in which
the work is placed on top of the table, were developed
later than the pull-up type. These pull-down machines
are capable of holding internal shapes to closer
tolerances by means of locating fixtures on top
of the work table. Machines come with pulling capacities
of 2 to 75 tons, 30 to 110 in. strokes, and speeds
up to 80 fpm.
Vertical Push Down Type
Vertical push down machines are often nothing more
than general-purpose hydraulic presses with special
fixtures. They are available with capacities of
2 to 25 tons, strokes up to 36 in., speeds as high
as 40 fpm. In some cases, universal machines have
been designed which combine as many as three different
broaching operations - such as push, pull, and surface
- simply through the addition of special fixtures.
Vertical Surface or Combination
This type is found mainly in the automotive and
hand tool industry. These machines produced in single-and
double-ram versions (and even more rams occasionally),
are hydraulically powered, with a few notable exceptions.
Capacities range from 3 to 50 tons, with up to 130-in.
strokes, and speeds of up to 120 fpm.
Vertical Surface Broaching Machines
These are available with either single or double
rams and with strokes up to 120 in., capacities
of 25 tons, and speeds of 60 fpm.
HORIZONTAL BROACHING MACHINES
The favorite configuration for broaching
machines seems now to have come full circle. The
original gear-or screw-driven machines were designed
as horizontal units. Gradually, the vertical machines
evolved as it became apparent that floor space could
be much more efficiently used with vertical units.
Now the horizontal machine, both hydraulically and
mechanically driven is again finding increasing
favor among users because of its very long strokes
and the limitation that ceiling height places on
vertical machines. About 40% of all broaching machines
are now horizontals. For some types of work, such
as roughing and finishing automotive engine blocks,
they are used exclusively.
Horizontal Internal or Combination
This type was among the first used after the advent
of powered broaching, have been driven hydraulically
for many years. Hydraulic drives, developed during
the early twenties, offered such pronounced advantages
over the various early mechanical driving methods
that only within recent years have any other methods
By far the greatest amount of horizontal
internal broaching is done on hydraulic pull-type
machines, for which configurations have become somewhat
standardized over the years. Fully one-third of
the broaching machines in existence are of this
type, and of these, nearly one-fourth are over twenty
years old. They find their heaviest application
in the production of general industrial equipment
but can be found in nearly every type of industry.
Hydraulically driven horizontal internal
machines are built with pulling capacities ranging
from 2l/2 to 75 tons, the former representing machines
only about 8ft. long, the latter machines over 35
ft. long. Strokes up to 120 in. are available, with
cutting speeds generally limited to less than 40
Horizontal Surface Broaching
This type accounts for only about 10% of existing
broaching machines, but this isn't indicative of
the percentage of the total investment they represent
or of the volume of work they produce. Horizontal
surface broaching machines belong in a class by
themselves in terms of size and productivity. Only
the large continuous horizontal units can match
or exceed them in productivity. Horizontal surface
units are manufactured in both hydraulically and
electro-mechanically driven models, with the latter
now becoming dominant.
The older hydraulically driven horizontal
surface machines now are produced with capacities
up to 40 tons, strokes up to 180 in., and normal
cutting speeds of 100 fpm. These machines, a major
factor in the automotive industry for nearly 30
years, turn out a great variety of cast-iron parts.
They use standard carbide cutting tools and some
of the highest cutting speeds used in broaching.
But electro-mechanically driven horizontal
surface machines are taking over at an ever-increasing
rate for certain applications, despite their generally
higher cost. Because of their smooth ram motion
and the resultant improvements in surface finish
and part tolerances, these machines have become
the largest class of horizontal surface broaching
units built. They are available with pulling capacities
in excess of 100 tons, strokes up to 30 ft., and
cutting speeds, in some instances of over 300 feet
Larger machines have fully stress-relieved
welde4d steel frames, rather than gray-iron castings.
Frequently two sets of cutting tools are attached
to the ram so parts can be broached on both the
forward and return strokes. A common operation on
automobile engine blocks is broaching head surfaces
on one stroke of the ram, and pan rail and bearing
surfaces on the return stroke.
These machines can also be equipped
with dual-speed controls, whereby the ram is driven
at one pre-selected speed during one portion of
the stroke and changed to a second pre-selected
speed during another portion of the stroke. A typical
application is the use of the high speed for the
initial roughing cut on pinetree slots in turbine
wheels, and the slower speed while the finishing
teeth are cutting.
Continuous Surface Horizontal
Chain Broaching Machines
These have been the most popular type of machine
produced for high-production surface broaching.
has the distinction of having built, the largest
and smallest service units ever produced.
The large continuous machine was a
42.5-ton giant with a 29-ft.-long bed, a 220-in.
stroke, and a 40-ton broaching capacity. It performs
nine separate operations on 71/2-lb., 121/2 in.-long
connecting rod-and-cap sets for farm-machinery engines.
The smallest was an 8.5-ton chain broach with a
2.5-ton capacity and a 20-in. stroke it broaches
5-oz., 2.5-in.-long manual transmission shaft shifters
in four different configurations for automobiles.
The key to the productivity of a continuous
horizontal broaching machine is elimination of the
return stroke by mounting the workpieces, or the
tools, on a continuous chain. Most frequently, the
tools remain stationary, mounted in a tunnel in
the top half of the machine, and the chain-mounted
workpieces pass underneath them.
SPECIAL BROACHING MACHINES
Special broaching machines also fall
under the general categories of internal or surface
use, but beyond that it is difficult to classify
the wide and often unique variety of special machines.
Nevertheless, here is a sampling.
Sometimes it is impossible to bring
the workpiece to the machine. This is particularly
true in the marine, power-generation construction,
and air-frame industries. Therefore broaching machine
builders have designed portable machines that can
be bought to the work.
A form of internal broaching called
strip broaching is used occasionally to effect large
gains in productivity per machine and man-hour through
reduced broaching time cycles. In strip broaching,
the broach is returned directly through the hole
just broached, immediately after the cutting stroke,
eliminating the necessity for disengaging the broach
tool from its pulling or pushing head. Broach life
is reduced because the cutting edges rub against
the work on the return stroke, but not to the extent
where the overall saving derived from this technique
Internal broaching of helicopter
rotor spar sections is an unusual special broaching
application. In one instance, a 24-ft. long workpiece
had about 1/8 in. of 4153 aluminum removed around
the periphery of the irregularly-shaped internal
form by 35 progressively stepped broach sections.
These were pulled through the workpiece one at a
time by a special electro-mechanical horizontal
machine with a 64-ft. long bed. Broach sections
were semi-automatically loaded and unloaded from
the pulling bar at the beginning and end of each
stroke. One operator handled the entire job, riding
from loading to unloading stations in an electric