The log feed is obtained by a motion separate from the return motion, there being three rates of feed and a quick return motion, the construction being as follows:
Referring to [Figs. 3149] and [3150], a is a belt pulley fast on the crank shaft, and driving pulley b, which is also shown dotted in. Pulley b drives the vertical shaft c, on which is the cone pulley d, having three steps, and which drives (by means of belt d′) cone pulley e, on which is a worm f, driving the worm wheel g, which runs idle on its shaft unless engaged therewith by means of the clutch h. The shaft of worm wheel g is omitted in [Fig. 3149], so as to leave the belt-shifting mechanism for pulleys q, q′ exposed to view. On this shaft however is a pinion driving the gear wheel k, on whose shaft is a pinion l, driving the gear m, which engages the rack n, on the under side of the carriage.
The clutch h is engaged by the lever i, to the upper arm of which is attached the rod j, j, from the lever p, hence operating p (which is done by hand), back and forth, throws clutch h into and out of gear with the worm wheel g, and puts the carriage feed on or throws it out, according to the direction in which p is moved.
The upper end of shaft c is carried in a bearing on the cross-head, and is provided with a featherway or spline, so that as the cross-head is raised or lowered the upper end of c passes through its upper bearing, and the pulley b travels with the cross-head. The three rates of carriage feed are obviously obtained by means of the three steps on the cone pulleys d and e.
We have now to explain the construction of the mechanism for traversing the table back, and giving it a quick return motion, or in other words a quicker motion on the back than on the feed traverse, and this is arranged as follows:
q, is a fast and q′, q′′, are loose pulleys, one driven by an open belt r, [Fig. 3150], and the other by a crossed belt r′, from a countershaft. The belt-shifting forks are operated by lever s, whose upper end engages with the rod t, which is operated by the lever u.
The loose pulleys q′ and q′′ are twice as wide as the fast pulley q.
Now suppose that lever u is moved to the right, and the belt would be moved from the loose pulley q′′ to the fast pulley q, while the other belt would merely be moved or shifted from one to the other side of loose pulley q′.
Similarly if lever u, be moved to the left, the belt on the loose pulley q′ will be moved on to the fast pulley q, and the belt on pulley q′′ would simply be moved across the face of the pulley, and as the countershaft pulleys for the two pulleys are of different diameters, therefore two rates of motion are obtained.
The shaft v, on which pulley q is fast, drives the pinion l, which drives m, the latter gearing with the rack beneath the carriage.