Smithy CNC Mills User Manual

Page 79

8.4.3 G92 Cautions

Sometimes the values of a G92 offset get stuck in the VAR file. When this hap-

pens reset or a startup will cause them to become active again. The variables

are named

5211 0.000000

5212 0.000000

5213 0.000000

5214 0.000000

5215 0.000000

5216 0.000000

where 5211 is the X axis offset and so on. If you are seeing unexpected posi-

tions as the result of a commanded move, or even unexpected numbers in the

position displays when you start up, look at these variables in the VAR file and

see if they contain values. If they do, set them to zeros and the problems

should go away.

With these tests we can see that reset returns g92 to the condition that it had

when the interpreter started up. The reader should note that we have estab-

lished ... that no write of these values occurs during a normal run so if no g92

was set at the startup, none will be read in during a reset.

It may be that this is the heart of the problem that some have experienced with

differences between the old and the new interpreter. It may well be, but I leave

to others to test, that the old interpreter and task programs immediately wrote

values to the var file and then found those values during a reset.

On the other hand, if G92 values existed in the VAR file when the EMC started

up... starting the EMC with g92 values in the var file is that it will apply the val-

ues to current location of each axis. If this is home position and home position

is set as machine zero everything will be correct. Once home has been estab-

lished using real machine switches or moving each axis to a known home posi-

tion and issuing an axis home command, g92 commands and values

work as advertised.

SmithyCNC Programmer’s Reference Manual: Coordinate System

8-8