An engineer's lathe is a machine which is principally used to produce circular boundaries on various pieces of work, and the machine consists of a long, heavy portion, named the bed, and three other principal portions, which are supported by the bed; these three are named, respectively, the spindle-frame or mandril-frame, the carriage, and the poppet-head. The mandril-frame is that in which the lathe spindle rotates to communicate its rotary motion to the work which is being turned. The various sizes of lathes are distinguished by the heights of their lathe spindles above the upper surfaces of the lathe beds; if the centre of the spindle is six inches above the bed, it is termed a six-inch lathe. In Plates 35 and 36 a few small lathes are shown, the sizes of which are about nine to eleven inches. In Plate 35 two lathes are represented, and a shaping-machine, which is situated between the two lathes. All the three machines are worked by means of the driving shaft above, which is fixed near the wall. This shaft is driven by either wind, water, steam, or any other agent that may be selected for the purpose. The wheels on this shaft are driving wheels, and communicate their rotary motion to the wheels of the lathes by means of the leather or india-rubber bands that are seen in the Figures, the direction of motion being indicated by the arrows which are seen in several places. In order to allow the lathe to be put to work and stopped without interfering with the motion of the driving shaft, an auxiliary shaft and its wheels are introduced between the driving shaft and the lathe, these wheels being properly arranged for the purpose. In the lathe at the right hand, the principal portions are named, and these names are the same in all other lathes, small and large. This lathe is one for ordinary turning, but not for screw-cutting. In this lathe the driving apparatus consists of one keyed wheel on the driving shaft and three wheels on the auxiliary shaft below; one of these three is termed a step drum, and is keyed tight at one end of the shaft; the other two wheels are termed pulleys; these are close together, and one of them is keyed tight on the shaft, but the other pulley is loose, and rotates without moving the shaft; this loose pulley is that which is rotated by the driving-shaft band when the lathe is not required to work; and to cause the band to rotate the auxiliary shaft, it is only necessary to move the band from the loose pulley to the tight one; when this is done, the step drum is also rotated, and because this is keyed tight to the shaft, the drum moves the lathe band, and the lathe spindle is made to work.

Plate 35

The starting and stopping machinery for moving the driving-shaft band consists of a fork having two prongs, which are in contact with the band's edges, also a straight rod in a vertical position at the farther side of the lathe, near the wall, and a starting handle at the lathe front, which is handled by the turner; these articles also are denoted in the Figure by two names and the letter F for fork.

When the lathe is at work both the carriage and the poppet-head are sometimes in use, this head being fastened at any desired place to suit the length of the work to be turned, and the carriage being moved along to carry the slide-rest denoted by S R, in which is fixed the cutting tool. In order to make the lathe itself move the carriage, a long rod or bar is employed, which is as long as the lathe; this is the traverse bar, and is situated at the side of the lathe farthest from the workman, termed the back of the lathe. This traverse rod is made to rotate by means of a teeth pinion, which is keyed to the small end of the lathe spindle ; this pinion drives another teeth-wheel, to the spindle of which is attached a small step drum, and a leather band from this drum drives another drum below, which is connected with the wheels that drive the traverse rod. On the traverse bar slides a worm pinion that drives a teeth-wheel, and this wheel is attached to a spindle in the carriage; consequently the carriage is moved slowly along the lathe bed by rotating the worm.