Re: [CAD_CAM_EDM_DRO] Homing position

Jeffrey T. Birt wrote:

>
>
> Many folks I talk to think that just installing some sort of home switch
> will give them the instant ability to stop/restart a job. The actuation
> position of the home sensor can be very repeatable but what about where your
> fixture/parts are? I use different fixtures all the time and mount them all
> over my table (to even out leadscrew wear.) An accurate home sensor will not
> tell me where my fixtures are. If I have an accurate home sensor and
> meticulously record the offset from the home position of each axis to some
> index-able position on my fixture my fixture and I know the offset from the
> fixture index position to my parts local zero than I can home, enter all the
> offset information, and be able to restart very close to where I left off.
> Usually though, in my experience it is easier to just rezero on the
> fixture/part and go from there.
>

The re-homing the next day picks up all offsets and workpiece coordinate
systems
as they were when the CNC program was shut down. This assumes you have
not removed the fixtures from the machine. Of course, you could have some
dowel pins or whatever set in the machine so fixtures could be repeatably
installed on the table.

You mention having to "meticulously record the offset", but at least EMC
does that
automatically and brings it back the next time the program starts.

> Some commercial machines have absolute encoders (scales) on each axis so it
> is easy to get the machine back to a precise position after a power cycle.
> But you still have to worry about maintaining the offset to your work.
>

The absolute encoder just lets you restart without homing, no big deal
on typical
machines. Takes less than a minute, and re-establishes all offsets to
one encoder
count.

Jon