Manual part programming for turning

Imagine standing in front of a lathe with the tool position at top right. If XO is the centre line of rotation, then all moves along that axis to produce a diameter will be away from you in a plus direction, i.e. X-r. All Z moves will be to your left in a minus direction, i.e. Z-. All moves will be in the top left X+Z- quadrant. It should be noted that X values relate to the diameter being produced, not the radius. 

When programming a turning operation X zero (XO) is always the centre of rotation. Z zero (ZO) is usually the front face of the workpiece as shown in Fig. 12.10. 

The dimension system can be absolute or incremental as described for milling incremental where the move is from the previous position and absolute where the move is the distance from a fixed datum (part zero). 

The lathe differs from milling in this function. 

In a word address programming system, a lathe uses X and Z to represent a move in absolute and U and W to represent an incremental move on the corresponding axes. (If you remember, milling used the codes G90 and G91.) 

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