HEIDENHAIN TNC 320 (340 55x-03) - Manual (Page 76)

76 4 Programming: Fundamentals of NC, File Management, Programming Aids
4.1 F
undamentals
Setting 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 “Coordinate
Transformation Cycles” on page 334).
If the production drawing is not dimensioned for NC, set the datum at
a position or corner on the workpiece which is 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. See “Setting the Datum
with a 3-D Touch Probe” in the Touch Probe Cycles User’s Manual.
Example
The workpiece drawing at right 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.
Y
X
Z
MAX
MIN
X
Y
325
320
0
450 900
950
150
-150
750
0
30
0±
0,
1
2 1
3 4
7
6
5