Hi Jon,

Do you mean to imply that your G53 and G54 coordinates are different.  
I've always thought and used G53 as if it was a non-modal G54 and  
therefore an easy way to use machine coordinates for a single move.  
eg. G53G0Z0 ... for manual tool change.

Dave
On Jul 28, 2007, at 10:43 PM, Jon Elson wrote:

> 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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