HEIDENHAIN TNC 620 (81760x-02) ISO programming - Manual (Page 96)

Programming: Fundamentals, file management
3.1 Fundamentals
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TNC 620 | User's ManualDIN/ISO Programming | 2/2015
Selecting the datum
A production drawing identifies a certain form element of the
workpiece, usually a corner, as the absolute datum. When setting
the datum, you first align the workpiece along the machine axes,
and then move the tool in each axis to a defined position relative
to the workpiece. Set the display of the TNC either to zero or to
a known position value for each position. This establishes the
reference system for the workpiece, which will be used for the
TNC display and your part program.
If the production drawing is dimensioned in relative coordinates,
simply use the coordinate transformation cycles (see User’s
Manual for Cycles, Cycles for Coordinate Transformation).
If the production drawing is not dimensioned for NC, set the
datum at a position or corner on the workpiece from which the
dimensions of the remaining workpiece positions can be most
easily measured.
The fastest, easiest and most accurate way of setting the datum is
by using a 3-D touch probe from HEIDENHAIN. See “Setting the
Datum with a 3-D Touch Probe” in the Cycle Programming User’s
Manual.
Example
The workpiece drawing shows holes ( 1 to 4 ) whose dimensions are
shown with respect to an absolute datum with the coordinates X=0
Y=0. Holes 5 to 7 are dimensioned with respect to a relative datum
with the absolute coordinates X=450, Y=750. With the DATUM
SHIFT cycle you can temporarily set the datum to the position
X=450, Y=750, to be able to program holes 5 to 7 without further
calculations.