HEIDENHAIN SW 68894x-02 - Manual (Page 45)

HEIDENHAIN CNC PILOT 640 45
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7
Fundamentals
Incremental coordinates
Incremental coordinates are always given with respect to the last
programmed position. They specify the distance from the last active
position and the subsequent position. Each position on a workpiece is
clearly defined by its incremental coordinates (see figure).
Polar coordinates
Positions located on the face or lateral surface can either be entered
in Cartesian coordinates or polar coordinates.
When programming with polar coordinates, a position on the
workpiece is clearly defined by the entries for diameter and angle (see
figure).
Machine zero point
The point of intersection of the X and Z axes is called the machine
zero point. On a lathe, the machine zero point is usually the point of
intersection of the spindle axis and the spindle surface. It is designated
with the letter "M" (see figure).