Re: [CAD_CAM_EDM_DRO] Re: EMC Stability

John Stevenson wrote:

> Jon Elson wrote:-
>
> >>> Second thing I picked up was a recent post about the BDI install
> >> resetting the referance points after a G30, end of program move. Has
> >> this been dealt with yet?
> >
> >G30? I suspect you mean M30, which was used to rewind the program paper
> >tape on Allen Bradley CNC controls. Officially, the RS-274D spec
> >calls M30 "end of data" and M02 "end of program". The more detailed
> >description doesn't really indicate much difference between the two
> >commands.
> >
> >Jon
> Sorry Jon this was a typo, It was getting late here <g> but you didn't
> answer the question.

Well, I can't. I'm embarrased to say I haven't installed the BDI yet.
I don't dare wreck a working machine, so I have to do it on another
computer. I will dig up a hard drive in the next few weeks and install
the BDI, just so I can know what quirks it might have.

>
> Also in a later post to whollid1 last night you stated:-
>
> >I generally try to forget there is even a machine coordinate system.
> >That is a detail for the CNC controller to worry about, and not for me.
> >The only place it really matters is when powering back up the next day,
> >you don't have to relocate your fixtures.
> >
> >Jon
>
> Am I correct then in thinking if you just switch off at the end of a job it
> forgets where you are and you have to re zero on start up ?

Yes, the encoders and counters do not stay powered up when the CPU is
off. With steppers, there is no way to know if the machine has been moved
manually, or if the steppers jumped a bit when the drivers were turned
off or back on. So, it is best to assume you don't know where you
are when EMC starts up.

EMC remembers the offset between machine coordinates and relative
(workpiece) coordinates by writing these down in the <something>.var
file when shutting down. If you have home switches, then the machine
coordinate system can be realigned, and so the work offset is automatically
reset to the way it was before.

So, pretty much you do have to re-home the machine every time you
start EMC, but you don't have to reestablish the work coordinate
reference.

Jon