Smithy CNC Mills - Manual (Page 78)

SmithyCNC Programmer’s Reference Manual: Coordinate System 8-7
G92 also works from current location as modified by any other offsets that are
in effect when the g92 command is invoked. While testing for differences
between work offsets and actual offsets it was found that a g54 offset could
cancel out a g92 and thus give the appearance that no offsets were in effect.
However, the g92 was still in effect for all coordinates and did produce expected
work offsets for the other coordinate systems.
It is likely that the absence of home switches and proper home procedures will
result in very large errors in the application of g92 values if they exist in the var
file. Many EMC users do not have home switches in place on their machines. For
them home should be found by moving each axis to a location and issuing the
home command. When each axis is in a known location, the home command
will recalculate how the g92 values are applied and will produce consistent
results. Without a home sequence, the values are applied to the position of the
machine when the EMC begins to run.
8.4.2 Setting G92 values
There are at least two ways to set G92 values.
* right mouse click on position displays of tkemc will popup a window into which
you can type a value.
* the g92 command
Both of these work from the current location of the axis to which the offset is to
be applied.
Issuing g92 x y z a b c does in fact set values to the g92 variables such that
each axis takes on the value associated with its name. These values are
assigned to the current position of the machine axis. These results satisfy para-
graphs one and two of the NIST document.
G92 commands work from current axis location and add and subtract correctly
to give the current axis position the value assigned by the g92 command. The
effects work even though previous offsets are in.
So if the X axis is currently showing 2.0000 as its position a G92 x0 will set an
offset of -2.0000 so that the current location of X becomes zero. A G92 X2 will
set an offset of 0.0000 and the displayed position will not change. A G92
X5.0000 will set an offset of 3.0000 so that the current displayed position
becomes 5.0000.