Fig. 30. Lathe having Quick Change-gear Mechanism
Quick Change-gear Type of Lathe.—A type of lathe that is much used at the present time is shown in [Fig. 30]. This is known as the quick change-gear type, because it has a system of gearing which makes it unnecessary to remove the change gears and replace them with different sizes for cutting threads of various pitches. Changes of feed are also obtained by the same mechanism, but the feeding movement is transmitted to the carriage by the rod R, whereas the screw S1 is used for screw cutting. As previously explained, the idea of using the screw exclusively for threading is to prevent it from being worn excessively, as it would be if continually used in place of rod R, for feeding the carriage when turning.
Fig. 31. End and Side Views of Quick Change-gear Mechanism
The general construction of this quick change gear mechanism and the way the changes are made for cutting threads of different pitch, will be explained in connection with [Figs. 30], [31] and [32], which are marked with the same reference letters for corresponding parts. Referring to [Fig. 30], the movement is transmitted from gear s on the spindle stud through idler gear I, which can be moved sidewise to mesh with either of the three gears a, b or c, [Fig. 31]. This cone of three gears engages gears d, e and f, any one of which can be locked with shaft T ([Fig. 32]) by changing the position of knob K. On shaft T there is a gear S which can be moved along the shaft by hand lever L and, owing to the spline or key t, both the sliding gear and shaft rotate together. Shaft T, carrying gears d, e and f and the sliding gear S, is mounted in a yoke Y, which can be turned about shaft N, thus making it possible to lower sliding gear S into mesh with any one of a cone of eight gears C, [Fig. 31]. The shaft on which the eight gears are mounted has at the end a small gear m meshing with gear n on the feed-rod, and the latter, in turn, drives the lead-screw, unless gear o is shifted to the right out of engagement, which is its position except when cutting threads.
