Machinery's Handbook, 31st Edition
1388 AXIS NOMENCLATURE movement away from the headstock is positive and movement toward the headstock is negative. Generally, there is no Y -movement.
Cross Slide
+Z
Z
+X
W
+X
+Z Carriage
+Y
Fig. 5. Fig. 6. The machine shown in Fig. 6 is of conventional design, but most NC lathes look more like that shown in Fig. 7. The same right-hand rule applies to this four-axis lathe, on which each turret moves along its own two independent axes. Movement of the outside-diameter or upper turret, up and away from the workpiece, or spindle centerline, is a positive X -motion, and movement toward the workpiece is a negative X -motion. The same rules apply to the U -movement of the inside-diameter, or boring, turret. Movement of the lower turret parallel to the Z -motion of the outside-diameter turret is called the W -motion. A popular lathe configuration is to have both turrets on one slide, giving a two-axis system rather than the four-axis system shown. X -and Z -motions may be addressed for either of the two heads. Upward movement of the boring head therefore is a positive X -motion.
+C
+X +U
+Z
+W
On a slant-bed lathe with 2 cross-slides, each tool turret can be operated independently, requiring four addresses, X , Y , U and W
Fig. 7. Axis nomenclature for other machine configurations is shown in Fig. 8. The letters with the prime notation (e.g., X ' , Y ' , Z ' , W ' , A ' , and B ' ) mean that the motion shown is positive, because the movement of the cutter with respect to the work is in a positive direction. In these instances, the workpiece is moving rather than the cutter.
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