Hello, all,

I was machining something this evening using a program which I 
had used some time ago under my 1999 version of EMC.  The 
behavior of fixture offsets seems to have changed.

Here's what I did :

I am using the Axis interface, I set the part coordinate system 
with the on-screen "touch off" button so the lower left corner 
of the part was (0,0).  The program has code like this :

G10 L2 P2 X9.5 Y1.5
G55

It then machines some features from a (0,0) coordinate 
reference, which it expects to be at x=9.5 y=1.5 in the G54
coordinate system.  When I tried to run this, I got "move 
exceeds soft limits" errors on both axes.  I fiddled around in 
MDI mode to try to figure out how the G10 L2 function works, and 
it seems you need to know the offset between the G53 and G54 
systems and use that in your calculation.  What I ended up doing 
was to go to G54, move to X9.5 Y1.5 in MDI and then switch to 
G55 and observe the coordinates on the display.  Let's say they 
were X=5.3 Y=-1.7  To get the current location to read as (0,0) 
I had to enter G10 L2 P2 X5.3 Y-1.7

This seems to be totally awkward, as it requires the program to 
know the difference between the machine coordinate system and 
the relative (work) coordinate system before the blank workpiece 
is even put on the machine.  Shouldn't all these fixture offsets 
be relative to G54, rather than G53?

I read all I could find in the .pdf user manual, and got more 
confused.  It seems to generally confirm the above is what is 
going on, but this seems very cumbersome.  Is there a simple way 
to align, say G55, to a precise offset from G54?  I NEVER, EVER, 
use the G53 system, and the only purpose I can imagine for it is 
to know where the machine limits are.

Getting out of EMC to edit the var file is not a good idea after 
you've used an edgefinder to locate the part's edges, either.

I am using a version of EMC2 that is a couple weeks old, early 
July.  Nothing in the bugfix list indicates any changes in this 
area, so I hope I'm not wasting anybody's time with this.

Jon.

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