HEIDENHAIN PT 855 for Turning - Manual (Page 7)

I - 1 Fundamentals of Positioning
8 Operating Instructions POSITIP 855
Datum setting
The workpiece drawing normally specifies the workpiece face as
the “absolute” datum, and indicates the axis of rotation. The
datum setting procedure assigns the origin of the absolute
coordinate system to this datum.
Z
X
T1 T2 T3
Determining and entering tool data
Your POSITIP display unit should show you the absolute position
of the workpiece regardless of the length and shape of the
particular tool being used. For this reason you must determine
the tool data (tool preset) and enter them. First touch the
workpiece with the cutting edge of the tool and then enter the
associated display value for that position.
You can enter tool data for up to 99 tools. When you have set
the datum for a new workpiece, all tool data are referenced to
the new workpiece datum.
See examples starting on page 19.
Cross slide, saddle and top slide
On conventional lathes, the tool is mounted on a slide that moves
in the direction of the X axis (the cross slide) and in the direction of
the Z axis (the saddle).
Most lathes have a top slide above the saddle. The top slide
moves in Z axis direction and is designated Z
O
.
Z
Z
O
X
+Z
+X
+Z
O
Fig. 3: Axes of movement on a lathe
Fig. 4: The origin of the Cartesian coordinate
system is the workpiece datum
Fig. 5: These tools have different tool data