Re: [CAD_CAM_EDM_DRO] G code Examples

Alan Marconett KM6VV wrote:

> Jon,
>
> Lots of useful information! I am interested in:
>
> G92 - Programming of absolute zero point (from NIST)
>
> As I understand it, G92 "sets" the controller's coordinates to that
> specified? And something is saved to a file, for the next time the
> machine is run? I'm not clear on what gets remembered. MaxNC remembers
> the last coordinates the machine was at (when restarted), is that part
> of G92's function?

To clarify, EMC remembers the OFFSET between home and the
coordinate reference you establish with a G92. The advantage here
is that (assuming you have accurate home switches) you can move
the machine manually when powered down, or move it under computer
control while lubing, cleaning, mounting parts, and then home it, and the
original coordinate system (from yesterday, for instance) will be back
in force. Assuming you have the home switches, this is much more
powerful than simply remembering last position, as the last position is
not very reliable. Someone could bump the machine and you wouldn't
know it.

This is important on servo machines, as the servos will often jump a bit
when servo power comes on. Steppers may jump a bit as power
comes on, too. Generally, that would be less than 2 steps, but it could
really accumulate if done repeatedly! (That happened in our shop with
an electronic indexing head, and ruined a few weeks work that was cut
wrong.)

Jon