respectively to first and second turrets or tool bases 3 and 4 for cutting the workpiece 10 the first and second turrets 3 and 4 are moved in the direction of the arrow to cause the cutting tools 5 and 6 to cut the workpiece 10 with the lathe according to the illustrated embodiment the workpiece is machined simultaneously by the two turrets 3 and 4 the chuck 1 is rotatably driven by a single spindle motor not shown as is well known in the art fig2 illustrates in block form the nc system of the present invention the nc system is composed of an input unit 12 having a reader for reading an nc tape 11 and includes a command interpretation and processing circuit a control unit cpu 13 a memory 14 an arithmetic processing unit 15 an output unit 16 and a setting and display unit 17 including a crt and a keyboard the lathe or machine tool as shown in fig1 which is controlled by the nc system of fig2 is indicated by reference numeral 18 fig3 is a flowchart of progressive steps 100 through 106 of nc machining operations effected by the nc system of the present invention the operation of the nc system shown in fig2 will be described with reference to fig3 various data items are entered in step 100 the data items to be entered include d 1 depth of cut for the first turret 3 mm d 2 depth of cut for the second turret 4 mm f 1 speed.