RE: Learning BDI Emc - Outputs, Home position

["Pete Cook" <pete.cook-at-alltracorp.com>]

Years ago machine tools didn't have such things as home switches - you
either ran in incremental mode (G90) or you ran in absolute mde (G90,
G92x?????Y?????) and your reference was some arbitrary point in space and
your first move or moves were to some point 0.100" off the top surface and
the side of the workpiece and you then adjusted the cutter position based on
how much extra material there was on the workpiece. Having 0 at the top of a
workpiece on a milling machine also makes it easy to figure depths for
checking dimensions from any line in the program for adjusting Z axis
offsets.

Also - for homing switches to be of real value they must be precision
switches with excellent repeatability or you are always having to adjust
your home ofsets and you never really trust them- which kind of defeats the
purpose of homing switches. Good homing switches let you shut off the
machine in the middle of a job and when you power it back up you are in a
known position and can then get to the right line in your program and hit go
and continue cutting on the same part. If you are not cutting multi-day
parts it really doesn't matter.

Pete Cook

> Of course the first thing I do is try out Deskam's Deskgrave
> and naturally
> it only allows a negative Z "cutting depth"  Arrrgh!  Search
> and replace.
> I guess most people think that z=0 is the top surface of the workpiece
> and that is why they like "negative" z cuts into the surface.
>