RE: [CAD_CAM_EDM_DRO] Question Re: Work Offsets

Jon,

Are your comments based upon the older RH 5.2 build or the newer BDI
build? I know that you were/are running the older version on your
Bridgeport. The handling of G92 offsets (what is done behind the scenes
when you do a right mouse click on an coordinate display and set a
position in manual mode) changed drastically from the RH 5.2 versions to
the new versions the BDI is based upon. In my balsa cutting program I
need to have a G92 position I call at the end of a program persist to
the next run. In the older EMC version it works perfectly. In the BDI
versions the G92 offsets are cleared on each program run and I get to
dive for the floor as my tooling heads to places I never intended.
Needless to say, I only use the older EMC version on that machine. All
other machines are instead converted to Mach2. I would change the EMC
machine also, but it is making me money so I am leaving alone what isn't
broken. Probably make the switch to Mach2 on it when I finally get
around to putting a 4th axis on that machine.

Tim
[Denver, CO]
Sherline products at Deep Discount
Mach1 & DeskCNC with credit card ordering
www.KTMarketing.com/Sherline

> -----Original Message-----
> From: Jon Elson [mailto:elson@...]
> Sent: Thursday, June 12, 2003 11:39 AM
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: Re: [CAD_CAM_EDM_DRO] Question Re: Work Offsets
>
>
>
>
> inetd_conf wrote:
>
> >I had some odd behavior on an EMC system running BDI 2.16:
> >
> >I spent the last two days PID tuning to get the axes running
> >cleanly. They're running cleanly now, and in the process I had the
> >opportunity to set up and run a number of toolpaths, mostly
> >prototyping in pine so a tool crash wouldn't be disastrous.
> >
> >Today I tried to run an actual part. I used an edge finder to
> >indicate in the workpiece, and set my zeros by right-clicking on
> >each axis in turn and setting it to zero.
> >
> >
> Unless your edge finder has a zero radius tip, O don't know
> how this can work. I usually use an edge finder with a .200"
> end, and set the axis to either -.100 or +.100" depending on
> which side of the part I am on. Just to protect against dumb
> mistakes, after setting both axes, I then do X0 Y0 in MDI
> mode, and manually set the edge finder to be centered. If I
> have made the wrong sign entry above, the error will be
> obvious, as it will be .200" off center from the part corner.
>
> >When I ran my program, it proceeded to crash the tool into the
> >workpiece (even though the first move is to go to (0,0,0) and raise
> >the quill to 2.0" off the top of the workpiece.)
> >
> >I carefully checked my zeros and loaded a new part. Same behavior,
> >only this time it snapped the end mill off.
> >
> >Before changing a tool and crashing it again, I played around with
> >it.
> >
> >In MDI mode, if I typed "G0X0Y0Z0", it would go to (0,0,0) in the
> >relative coordinate frame. If I ran the program, it would attempt
> >to go to (0,0,0) in the absolute machine coordinate frame (the Z
> >value of which was well inside the workpiece).
> >
> >
> I know you have set X and Y with the edgefinder, but did you
> set the Z axis to the right coordinate offset?
>
> >I stripped the entire header off the program file so it starts with
> >that "G0 X0.000 Y0.000 Z0.000" statement. Same behavior.
> >
> >What am I missing here? I thought MDI and running a program was
> >essentially the same thing. I didn't know one would run in one
> >coordinate frame and one would run in the other. I'm REALLY puzzled
> >why this behavior didn't show up during the two days of PID tuning I
> >did.
> >
> >
> It may require you to have the SCREEN DISPLAY set to
> "Relative" mode when you set the axes from the screen. If
> the screen is displaying absolute coordinates, then the
> screen buttons to set the axes will set the ABSOLUTE coords
> to zero, not the RELATIVE coords, which is what you want.
>
> Jon