HEIDENHAIN TNC 426 B, User Manual

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4 Programming: Fundamentals of NC, File Management,
Programming Aids, Pallet Management
Y
X
Z
Selecting the datum
A production drawing identifies a certain form element of the
workpiece, usually a corner, as the absolute datum. Before setting
the datum, you align the workpiece with the machine axes and
move the tool in each axis to a known position relative to the
workpiece. You then set the TNC display to either zero or a
predetermined position value. 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. For further
information, refer to section 8.7 “Coordinate Transformation
Cycles.”
If the production drawing is not dimensioned for NC, set the datum
at a position or corner on the workpiece, which is the most suitable
for deducing the dimensions of the remaining workpiece positions.
The fastest, easiest and most accurate way of setting the datum is
by using a 3-D touch probe from HEIDENHAIN. For further
information, refer to section 12.2 “Setting the Datum with a 3-D
Touch Probe.”
Example
The workpiece drawing at right illustrates the holes to , which
are dimensioned to an absolute datum with the coordinates X=0
Y=0. The holes to are referenced to a relative datum with the
absolute coordinates X=450 Y=750. By using the DATUM SHIFT
cycle you can shift the datum temporarily to the position X=450,
Y=750 and program the holes to without any further
calculations.
4.1 Fundamentals of NC
X
Y
325
320
0
450 900
950
150
-150
750
0
300
±
0,
1
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