Page:Practical Treatise on Milling and Milling Machines.djvu/89

Rh horizontal spindle machines. The construction in each case can be readily understood, as it consists of nothing other than a pair of gears for increasing the speed and an auxiliary spindle that drives the cutter.

Slotting Attachment. This attachment, shown in Fig. 38, is largely used in tool making, such as in forming box tools for screw machines, making templates, splining keyways, and work of a similar character. The working parts consist of a tool slide that is driven from the machine spindle by an adjustable crank that allows the stroke to be set for different lengths. The attachment can be set at any angle between and 90°, either side of the centre line, the position being indicated by graduations on the circumference of the head. The tool is held in place by a clamp bolt, and a tool stop that swings over the top of tool shank makes it impossible for the tool to be pushed up.

Attachment for Cutting Short Leads. In cutting spirals with a spiral head, as the lead becomes shorter and a higher ratio of gearing becomes necessary, the stress upon the gears and mechanism becomes greater. For this reason, it is impractical to cut very short leads in this way. The attachment shown in Fig. 39 is designed particularly for use when it is desired to cut short leads.

It consists of a casting clamping over the dovetail of the spiral head carrying a swiveling gear plate and a short shaft which is driven from the rear of the machine spindle by a belt.

The work is rotated from the spindle independently of the feed screw, the latter being disconnected from the power feed mechanism.