A lathe for screw-making, which is represented in the left of Plate 35, has, in addition to the ordinary traversing apparatus, a few other attachments, named, respectively, the principal lathe-screw, the screwing-wheels, apron, and backward band. In the Figure the screw is fixed at the front near the workman, and is made to move the carriage and tool-rest along the bed when a screw is to be made, instead of moving the tool by means of the ordinary traverse bar and worm. Teeth-wheels are required to rotate the lathe-screw, which are termed screwing wheels, and the apron is that which is attached to the carriage, and contains the screw-nut, which fits the thread of the lathe-screw. By this arrangement the teeth-wheels rotate the screw, and the screw-thread pulls the apron and carriage along, because the screw-nut is fixed to the apron.

In the Figure the backward band is shown, which is actuated by the same drum-wheel that drives the forwarding band, and the backward band is crossed, to produce a backward movement of the lathe spindle, which is necessary during the process of making a screw. In order to make this backward motion quicker than the forward one, the wheels on the auxiliary shaft, which are rotated by the backward band, are smaller than the wheels which are rotated by the forward band ; and by referring to the Figure it may be observed that three wheels are required for each band, and that each three are situated close to each other. By means of these six wheels, or pulleys, as they are termed, the two bands are allowed to either travel around the driving shaft without moving the auxiliary shaft, or to work the auxiliary shaft and lathe forwards, or to work the lathe backwards when screwing is being effected. Of the six wheels two are keyed tight on the shaft, and four are loose, one tight wheel belonging to the forward band, and the other tight wheel belonging to the backward band. In the arrangement shown in the Figure, the two tight wheels are close together, and the four loose ones are outside. A two-prong fork is shown for each band, and both bands are moved at one time by the workman moving both forks at one time. The principal situations of the bands on the pulleys are three in number, one for the forward movement, the second for the entire stoppage of the lathe, and the third for the backward movement. The particular situation selected for the Figure is the first mentioned, by which the forward band is shown to be on its tight wheel, and the backward band is seen to be on one of its loose wheels; while in this condition the lathe spindle rotates forwards until the turner desires to alter the direction of motion or to stop the lathe, at which time he shifts the two bands at one time, and causes them to travel around the two loose wheels immediately adjoining the two tight ones; each of these two loose wheels is the middle one of each three, and while the two bands are on these two middle wheels, the entire motion of the lathe is stopped; consequently, when the workman wishes to stop all motion, he moves the two bands only sufficient to place them upon the two middle wheels, and fixes the starting handle in a suitable notch, to prevent movement; but if he desires to make the lathe spindle rotate backwards, he continues shifting the bands until the backward band is put upon its tight wheel, and the forward band is put upon its outside loose wheel; while thus arranged, the backward motion continues until the operator desires to stop the process or alter the direction of movement, which he effects by shifting the two bands to their former situations.