HEIDENHAIN ND 920 - Manual (Page 5)

5
Datum setting
The workpiece drawing is used as the basis for machining the
workpiece. To enable the dimensions in the drawing to be converted
into traverse distances of machine axes X, Y and Z, each drawing
dimension requires a datum or reference point on the workpiece (since
a position can only be defined in relationship to another position).
The workpiece drawing always indicates one absolute datum (the
datum for absolute dimensions). However, it may contain additional
relative datums.
In the context of a numerical position display unit, datum setting means
bringing the workpiece and the tool into a defined position in relation to
each other and then setting the axis displays to the value which
corresponds to that position. This establishes a fixed relationship
between the actual positions of the axes and the displayed positions.
You can set up to 99 absolute datum points and store them in
nonvolatile memory.
0
325 450 700 900 950
0
320
750
1225
300±0,1
0
150
-150
0
0
216,5
250
-250
-125
-216,5
0 -125 -216,5
-250 250
125 216,5
125
Fundamentals
Absolute
datum
Relative
datums