Fig. 573.
In the lathe shown in [Fig. 572], which is from the design of S. W. Putnam, of the Putnam Tool Company of Fitchburg, Massachusetts, the cone pinion for the back gear, and that for driving the feed motion, are of the same diameter and pitch, so that the gear-wheel l in [Fig. 573] may (by means of a lever shown dotted in) be caused to engage with either of them. When the latter is used in single gear it would obviously make no difference which wheel drives l, but when the back gear is put in and l is engaged with the cone pinion, its speed corresponds to that of the cone, which being nine times faster than the live spindle, enables the cutting of threads nine times as coarse as if the back gear was not in use. This affords very great advantages for cutting worms and threads of coarse pitches.
Fig. 574.
An excellent method of changing the direction of feed motion, and of starting or stopping the same, is shown in [Fig. 574], which represents the design of the Ames Manufacturing Company’s lathe.
In the figure, a is the small step of the lathe cone, b the pinion to drive the back gear, c a pinion to drive the feed gear, giving motion to d, which drives e, the latter being fast to g and rotating freely upon the shaft f, g drives h, which in turn drives i. The clutch j has a featherway into which fits the feather c, on the shaft f, so that when the clutch rotates it rotates j through the medium of c; k is a circular fork in a groove in j, and operated by a lever operated by a rod running along the front of the lathe bed. This rod is splined so that a lever carried by the apron or feed-table, having a hub and enveloping the rod, may by means of a feather filling into the spline operate the rod by partly rotating it, and hence operate k. Suppose now that this lever stands horizontal, then the clutch j would stand in the position shown in the cut, and d, e, g, h, and i, would rotate, while f would remain stationary. By lifting the lever, however, j would be moved laterally on f (by means of k) and the lug a on j would engage with lug b on g, and g would drive j, which through c would drive f, on which is placed a change gear at l, thus traversing the carriage forward. To traverse it backward the lever would be lowered or depressed below the horizontal level moving k, and therefore j, to the right, so that lug a would engage with lug b on i, hence f would be driven by i, whose motion is in an opposite direction to g, as is denoted by the respective arrows.
To throw all the feed motion out of gear, to run the lathe at its quickest for polishing, &c., the operation is as follows.
m is tubular and fast in n and affords journal bearing to wheel d. Through m passes stud o, having a knob handle at p. At the end of the hub of d is a cap fast in d, the latter being held endways between the shoulder shown on o and the washer and nut t. If then p be pulled outwards o will slide through m, and through the medium of t will cause d to slide over m, in the direction of the arrow, and pass out of gear from c, motion therefore ceasing at c.