11.1 Milling-machine elements
The main elements of a typical knee-and-column horizontal milling machine are shown in Fig. 11.3. The elements of a vertical machine are the same except that the spindle head is mounted at the top of the column, as shown in Fig. 11.4.

Column and base
The column and base form the foundation of the complete machine. Both are made from cast iron, designed with thick sections to ensure complete rigidity and freedom from vibration. The base, upon which the column is mounted, is also the cutting-fluid reservoir and contains the pump to circulate the fluid to the cutting area.
The column contains the spindle, accurately located in precision bearings. The spindle is driven through a gearbox from a vee-belt drive from the electric motor housed at the base of the column. The gearbox enables a range of spindle speeds to be selected. In the model shown, twelve spindle speeds from 32 to 1400rev/min are available. The front of the column carries the guideways upon which the knee is located and guided in a vertical direction.



Figure 11.3 Main machine elements of horizontal milling machine


Figure 11.4 Top of column of vertical milling machine

Knee
The knee, mounted on the column guideways, provides the vertical movement of the table.
Power feed is available, through a gearbox mounted on the side, from a separate built-in motor, providing a range of twelve feed rates from 6 to 250 mm/min. Drive is through a leadscrew, whose bottom end is fixed to the machine base. Provision is made to raise and lower the knee by hand through a leadscrew and nut operated by a handwheel at the front. The knee has guideways on its top surface giving full-width support to the saddle and guiding it in a transverse direction.
A lock is provided to clamp the knee in any vertical position on the column.

Saddle
The saddle, mounted on the knee guideways, provides the transverse movement of the table.
Power feed is provided through the gearbox on the knee. A range of twelve feeds is available, from 12 to 500 mm/min. Alternative hand movement is provided through a leadscrew and nut by a handwheel at the front of the knee.
Clamping of the saddle to the knee is achieved by two clamps on the side of the saddle.
The saddle has dovetail guideways on its upper surface, at right angles to the knee guideways, to provide a guide to the table in a longitudinal direction.

Table
The table provides the surface upon which all workpieces and workholding equipment are located and clamped. A series of tee slots is provided for this purpose. The dovetail guides on the undersurface locate in the guideways on the saddle, giving straight-line movement to the table in a longitudinal direction at right angles to the saddle movement.
Power feed is provided from the knee gearbox, through the saddle, to the table leadscrew. Alternative hand feed is provided by a handwheel at each end of the table. Stops at the front of the table can be set to disengage the longitudinal feed automatically in each direction.

Spindle
The spindle, accurately mounted in precision bearings, provides the drive for the milling cutters. Cutters can be mounted straight on the spindle nose or in cutterholding devices which in turn are mounted in the spindle, held in position by a drawbolt passing through the hollow spindle. Spindles of milling machines have a standard spindle nose, shown in Fig. 11.5, to allow for easy interchange of cutters and cutter-holding devices. The bore of the nose is tapered to provide accurate location, the angle of taper being 16° 36'. The diameter of the taper depends on the size of the machine and may be 30, 40, or 50 IST (International Standard Taper). Due to their steepness of angle, these tapers - known as non-stick or self-releasing - cannot be relied upon to transmit the drive to the cutter or cutter-holding device. Two driving keys are provided to transmit the drive.



Figure 11.5 Standard milling-machine spindle nose

Cutters which are mounted directly on the spindle nose are located on a centring arbor, and four tapped holes are provided to hold the cutter in position. The two keys again provide the means of transmitting the drive. 
The spindle of a horizontal machine is fixed and cannot be adjusted in an axial direction, i.e. along its axis. On vertical machines, provision is made for axial movement, which is controlled by a handwheel on the spindle head. The spindle runs in a quill which is moved through a rack and pinion in the same way as a drilling machine spindle (see Fig. 7.2). A locking bolt is provided to lock the quill in any position along its operating length.

Overarm and arbor support
The majority of cutters used on horizontal machines are held on an arbor which is located and held in the spindle. Due to the length of the arbors used, support is required at the outer end to prevent deflection when cutting takes place. Support is provided by an arbor-support bracket, clamped to an overarm which is mounted on top of the column in a dovetail slide. The overarm is adjustable in or out for different lengths of arbor, or can be fully pushed in when arbor support is not required. Two clamping bolts are provided to lock the overarm in any position. The arbor support is located in the overarm dovetail and is locked by means of its clamping bolt. A solid bearing is provided in which the arbor runs during spindle rotation