Re: [Emc-users] Fixture offsets ?

[Dale <da...@1s...>]

Jon,

  I use g53 quite a bit mainly to move to a known position relative to 
the machine cooardinate system. I also use g53 when setting a drinn in 
the collet. I use MDI to g0 z0. set tool to the top of the part, tighten 
the collet then g53z0 since z0 is spindle full up then at the end of 
every program is a g53 x0 y0 z0 after retracting to a safe z position.

All g5n.n coordinate positions should be in referance to the machine 
coordinate position (g53) for that matter all is relative to the machine 
cooardinate system in order to use soft limits without referring to the 
g54 settings and then back to g53. If you want to precisely define g55 
relative to g54 then in MDI it's as simple as g0 g54 x 2.5625 y 3.5 then 
in Manual set g55 to the current position. I'd have to look up how to do 
it under program control or using any version of EMC2. I'm sure there's 
more than one way to do that.

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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