HEIDENHAIN TNC 620 User Manual page 373

10.3 Miscellaneous functions for
coordinate entries
Programming machine-referenced coordinates: M91/
M92
Scale datum
On the scale, a reference mark indicates the position of the scale
datum.
Machine datum
The machine datum is required for the following tasks:
Define the axis traverse limits (software limit switches)
Approach machine-referenced positions (e.g. tool change
positions)
Set a workpiece datum
The distance in each axis from the scale datum to the machine
datum is defined by the machine manufacturer in a machine
parameter.
Standard behavior
The TNC references coordinates to the workpiece datum.
Further Information: Datum setting without a 3-D touch probe,
page 505
Behavior with M91 – Machine datum
If you want the coordinates in a positioning block to be referenced
to the machine datum, end the block with M91.
If you program incremental coordinates in an
M91 block, enter them with respect to the last
programmed M91 position. If no M91 position is
programmed in the active NC block, then enter the
coordinates with respect to the current tool position.
The coordinate values on the TNC screen are referenced to the
machine datum. Switch the display of coordinates in the status
display to REF .
Further Information: Status displays, page 80
HEIDENHAIN | TNC 620 | Conversational Programming User's Manual | 10/2015
Miscellaneous functions for coordinate entries 10.3
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