The driving pulley for the saw arbor is shown at c, [Fig. 3112], in dotted lines and in [Fig. 3113] in full lines. Upon the saw arbor is a cone pulley d, [Fig. 3113], for operating the carriage to the feed, the construction being as follows:
Fig. 3113.
Referring to [Figs. 3112] and [3113], cone pulley d connects by a crossed belt to cone pulley e, on whose shaft is a pulley e which drives the pulley f, on whose shaft is the pinion f, which drives the gear g. On the same shaft as g is a pinion g, which drives the gear wheel h, which engages the rack j, on the carriage, and feeds the carriage to the cut. The diameters of pulleys e, f, and of f, g, and g, are proportioned so as to reduce the speed of the cone pulley d, down to that desirable for the carriage feed. But, as there are four steps on the cones d, e, therefore there are four rates of cutting feed or forward carriage traverse, which varies from 15 to 30 feet per minute.
The speed of the saw varies in practice, some running it as slow as 9,000 feet per minute at the periphery of the saw, and others running it as high as 16,000 feet per minute. The latter speed however, is usually obtained when the saws are packed with fibrous packing, which will be explained presently.
The quick return motion for the carriage is obtained as follows:
Referring to [Figs. 3113], and [3114], k is a fast and k′ a loose pulley on the shaft k, and receiving motion by belt from a countershaft.
The speed of the fast pulley k is such as to give a return motion to the carriage of about 50 or 60 feet per minute, being about twice as fast as the carriage feed motion.
We have now to explain the methods of putting the respective carriage feed motions into and out of operation, and insuring that both shall not be in gear at the same time.