Major components of a Milling Machine

Regardless of whether the machine is of the vertical or horizontal type, several components on all knee-and-column milling machines are similar, except for size and minor variations because of manufacturer's preference. These similarities are described in terms of general shape, geometric relationship to the rest of the machine, function, and the material from which the components are made.

1)Column
The column, which is usually combined with the base as a single casting, is cast gray iron or ductile iron. Recently ductile iron has been used almost exclusively for castings of this type because it is stronger than gray iron, more stable and capable of being surface-hardened. The column houses the spindles, bearings, and the necessary gears, clutches , shafts, pumps and shifting mechanisms for transmitting power from the electrical motor to the spindle at the selected speed. The gears usually run in oil and are made of carburized alloy steel for long life. Some of the necessary controls are usually mounted on the side of the column. The base is usually hollow and in many cases serves as a sump for the cutting fluid. A pump and filtrationsystem can be installed in the base. The hole in the center of the base is the support for the screw that raises and lowers the knee. The machined vertical slide on the front of the column may be of the square or dovetail type. The knee moves up and down on this slide. The slide must be machined at a 90 degrees angle to the face of the column in both the lateral and vertical planes. The tolerances are very close and are usually expressed in minutes(1/60 of 1 degree)or seconds(1/3600 of 1 degree)of the arc. The large hole in the face of the column casting is for the spindle. The hole is very accurately bored perpendicularl to the front slide in two planes and parallel to the upper slide. On some Milling machines, the overarm consists of one or two heavy steel bars that an be moved forward to carry the outboard support for the arbor on which milling cutters are mounted. On Milling machines with a single quality gray cast iron or ductile iron and is usually partly hollow. A dovetail slide is machined on its lower face and this mates with corresponding dovetails on the top of the column and on the overarms support. Cast overarms are very rigid and are usually found on heavier and more powerful machines.

2)Spindle
On a horizontal milling machine, the spindle is one of the most important parys. It is usually machined from alloy steel forgig and is heat-treated to resists wear, vibration, thrust and bending loads. The spindle is usually supported by a combination of ball and straight roller bearings that absorbs both radial loads(perpendicular to the center lines of the spindle) and end thrust loads(in line with the spindle). Spindles are hollow so that a drawbar can be used to hold arbors. The front of the spindle is machined to accept standard arbors. The actual driving of the arbors is done by the two keys that fits into the corresponding slots in the arbors. The internal tapers, which is accurately ground so that it is concentric with the spindle, locates the arbors.

3)Knee
The knee is a casting that is moved up or down the slide on the front of the column by the elevating screw. Two dovetail or square slides are machined at 90 degrees to each other. The vertical slide mates with the slide on the front of the column, and the horizontal slide carries the saddle. The casting is for a largere Milling machine. It contains the necessary gears,screws and other mechanisms to provide power feeds in all directions. Various feed rates can be power selected by the operators with the controls mounted on the knee.

4)Saddle
The saddle for a plain milling machine is a casting with two slides machined at an exact 90 degrees angle to each other. The lower slide fits the slide on top of the knee, and the upper slide accepts the slide on the bottom of the table. The surfaces of the slides that make contact with the knee and the table are parallel to each other. Locks for both the cross slides and table are fitted to the saddle, along with the nuts that engage with cross feed and table screws.

5)Table
The tables vary graetly in size, but generally they have the same physical characteristics. The bottom of the table has a dovetail slide that fits in the slide on top of the slide. It also has bearings at each end to carry the table feed screw. The top of the table is machined parallel with the slide on the bottom and has several full-length T slots for mounting vises or other work-holding fixtures.

6)Vertical Milling machine
Milling machines with vertical spindles are available in alarge variety of types and sizes. The head, which houses the spindle, motor and feed controls is fully universal and can be placed at a compound angle to the surface of the table. The ram, to which the head is attached, can be moved forward and back and locked in any position. A turret on top of the column allows the head and ram assembly to swing laterally, thus increasing the reach of the machine