| Milling machines are a very versatile machine tool. Milling
machines are capable of machining one or two pieces as well as large
volume production runs. The milling machine can produce a variety of
surfaces by using a circular cutter with multiple teeth that
progressively produce chips as the cutter rotates (Figure 1). |
Figure 1. Carbide face mill used on
a vertical milling machine.
|
The advantage of having a circular milling cutter with multiple teeth
has led to the design of a large variety of milling machine types. These
different milling machine types can be classified as Knee and Column,
Fixed Bed, Bridge Type, and Special. All of these classifications can have
either a vertical or horizontal spindle configuration. Further
classifications of milling machines are made on the basis of the type of
computer numerical control the machine uses.
Knee
and Column Type Milling Machines
| The knee and column type milling machine is a very versatile
machine (Figure 2). This type of milling machine is found primarily
in job shops and tool and die shops. |
Figure 2. Vertical Knee and Column
type milling machine.
|
|
Figure 3. Horizontal Knee and Column
type milling machine.
|
The most distinguishing characteristic of this type of machine is
the knee and column configuration (Figure 3).
This type of milling machine is unique in that the table can be
moved in all three directions.
The table can be moved longitudinally in the X-axis as well as in
and out on the Y-axis. Since the table rides on top of the knee, the
table can be moved up and down on the Z-axis. There are several
different types of knee and column type milling machines, but they
all have the same characteristic. The knee slides up and down on the
column face. |
Universal
Knee and Column Milling Machine
| The universal knee and column milling is very similar to the plain
knee and column milling machine. The largest difference being the
swiveling table housing. The swiveling table housing allows the
table to be swiveled at an angle to the axis of the spindle (Figure
4). |
 
Figure 4. Universal Horizontal Knee
and Column Milling Machine with the swivel table.
|
Vertical
Knee and Column Type Milling Machine
| A vertical type knee and column milling machine has the spindle
located vertically, parallel to the face of the column, and
perpendicular to the top of the table.
The ram style knee and column type milling machine is a light
duty milling machine (Figure 5). This type of machine is well suited
for a variety of tool room work as well as other light duty
operations. The head is mounted on a ram that can be swiveled or
brought forward. This allows the head to be brought into an
operating position over most of the table. |
Figure 5. Ram Style Knee and Column
Type Vertical Milling Machine.
|
Fixed
Bed Type Milling Machines
| The most distinguishing aspect of the fixed bed type milling
machine is the absence of the knee (Figure 6). |
Figure 6. Fixed Bed Horizontal
Milling Machine.
|
Figure 7. CNC Vertical Spindle
Bed-Type Milling Machine. |
The fixed bed construction of this style of milling machine
minimizes deflection and allows very heavy cuts to be taken. Fixed
bed style milling machines can be used for general purpose work
although many people look upon them as high production machines. The
table can move in a longitudinal and a transverse direction. The
vertical position of the spindle, with respect to the work table, is
obtained by moving the head up and down along the column of the
machine (Figure 7). |
Bridge
Type Milling Machines
| The construction of the Bridge Type milling machine resembles that
of a bridge (Figure 8).
The table is mounted on the bed. On either side of the bed are
two vertical columns connected at the top by a brace. A cross rail
is mounted on the brace. The cross rail houses the spindle head.
Bridge type milling machines are typically used to machine large
pieces such as castings, machine tables and housings. |
Figure 8. CNC Vertical Bridge-Type
Milling Machine.
|
Special
Milling Machines
| There are a number of types of special milling machines. Special
milling machines are designed specifically for one particular part
or family of similar parts. Specialty milling machines are used
extensively in the automotive and aeronautics industry. The
specialty milling machine in Figure 9 is used to mill screws used in
large extruding machines. |
Figure 9. Extrusion Screw milling
Machine.
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