Page:Practical Treatise on Milling and Milling Machines.djvu/90

84 The regular index change gears are used on the swiveling gear plate to connect with the large index gear to give the work the proper speed of rotation. The lead is obtained as described on pages 58 to 63, allowing the rotation of the work to drive the table feed screw. Eighteen holes in the large index gear allow indexing when cutting multiple threads.

A rack cutting attachment or vertical spindle milling attachment is used to drive the cutter.

Spiral Milling Attachment. This attachment, shown in Fig. 40, is designed for the heavy class of spiral cutting in conjunction with the spiral head. The cutter is placed on the end of cutter spindle, allowing attachments to cover a large variety of work. In addition to cutting spirals, attachments can be used for cutting racks. The spindle can be set at any angle in a horizontal plane.

Rack Cutting Attachment. An attachment for cutting teeth in racks is shown in Fig. 41. It can also be used in connection with the spiral head for cutting worms, on Universal Milling Machines, as shown on page 173, and for other miscellaneous operations.

The cutter is mounted on the end of a hardened steel spindle that extends through the attachment case parallel to the table T slots. This spindle is powerfully and smoothly driven from the machine spindle by a train of hardened steel bevel and spur gears.

A vise, the construction of which can be plainly seen in the cut, is furnished as a part of the attachment.

When cutting racks, some convenient means of indexing to quickly and accurately space the teeth is