Work Spindle Arrangement

The work spindle projects through the bearings at each end. At the right it is usually threaded to receive a faceplate F, and is also bored out and tapered for a work center G. This center is called the live center because it turns with the spindle. The dead center H is in the tailstock, and does not turn. At the left the work spindle projects beyond the bearings and presses axially against a thrust step. The cone pulley I serves as the driving pulley for a narrow belt running to the corresponding pulley K on the feed rod N. The pinion J drives the lead-screw 0 through the intermediate gear M and the direct gear L.

Fig. 95. Typical Engine Lathe.

Handling the Work

The work is held on the centers G and H, the distance between which is adjusted by moving the tailstock S (sometimes called the tailblock). The latter is held to the bed by a clamp and bolts tightened by the nuts T. To move the tailstock, these nuts are slackened and the stock moved to the proper position. The final adjustment is made by turning the hand wheel Q, which rotates a screw in the sleeve P. Sleeve P works in a nut in the spindle of the dead center H, which is thus moved in and out. When the centers have been properly adjusted and the work is in position, the dead center is clamped by the handle R.

When work is to be turned, the tool is properly adjusted, and the carriage U moved along the bed. This movement is accomplished by means of gearing, which is placed behind the apron of the carriage, and driven by the shaft N by the cone pulley K, which is keyed to shaft N. The driving gearing meshes with a rack beneath the upper ledge of the bed. Connection between the gearing and shaft N is made by a friction clutch. The carriage may also be moved by hand, by turning the hand wheel V, to which is keyed a pinion indirectly meshing into the rack.

Tool-Feeding Mechanism

The tool is fed to the work and withdrawn from it by turning the cross-feed handle W. By means of the screw and nut, this moves the cross-slide X. These arrangements permit any desired transverse or longitudinal position of the tool. The motion of the carriage is usually from right to left when at work. When screws are to be cut, a different feed is used. In ordinary turning, there will be a variation in the relations between the rotation of the work and the longitudinal motion of the tool, due to the slipping of the belt connecting the cone pulleys I and K, or to the slipping of the friction clutch which connects the shaft N to the driving gear. To cut a screw-thread, it is necessary that there shall be no relative change in the rotation of the work and the longitudinal motion of the tool. In other words, the tool must travel a given distance for every revolution of the work. To accomplish this, the carriage is driven by the lead-screw 0 working in a nut set in the carriage. The screw is, in turn, driven by the train of gears J, M, and L. The gear J is keyed to the stud. The intermediate gear M runs loose on a sleeve. The gear L is keyed to the lead-screw 0. By changing the sizes of the gears used on the stud and the screw, any desired thread may be cut. The size of the intermediate gear M has no effect on the thread being cut. This gear M is used to connect the other two gears L and J and can be adjusted to any desired position for that purpose.

Fig. 96. Typical Set-Up of Gears on Lathe Using Back Gear.