Fig. 1897.
Referring to [Fig. 1897] the hand wheel operates a worm engaging with a worm-wheel on the shaft of the largest gear shown in the engraving. From this gear motion is conveyed through intermediate wheels to the pinion on the same shaft as the first bevel-gear, which obviously drives the bevel-gear shown on the end of the head. The back face of this latter gear is provided with index holes, and the usual index arm and pin are provided.
The change gears provided for this device are sufficient to cut twelve different pitches, ranging from one turn in 2 inches to one turn in 6 feet. Obviously right or left-hand spirals are produced according to the direction of revolution of the hand wheel.
In the general view, [Fig. 1898], the device is placed upon a box bolted to the work table, and obtains its automatic feed through the medium of the worm for the table feed.
Fig. 1899.