Re: [CAD_CAM_EDM_DRO] Question Re: Work Offsets

On Thu, 12 Jun 2003, Jon Elson wrote:

> 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.

That's exactly what I did. My edge finder has a 0.200" wide tip. So I
brought it up against the two edges, shifted it by +0.100 +0.100, and set
that to x=0 y=0. I then switched to my tool, brought the tip down until
it was kissing the top of the workpiece and set that to be z=0. In MDI, a
G0X0Y0Z0 would always return the tool to that position. Which is why I
was so suprised when a G0X0Y0Z0 in the program drove the tool straight
into the work piece.

I'm not talking about a small offset here. It buried the mill about 1"
deep in the material before it snapped off.

Tom

> >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
>
>
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