Re: DIY probing

Hi Jim,

Thanks for the comments. I like the idea of specifying your own grid.
I think that is easily possible, as using a G31 (G61) command can be
used to do a linear move with sense. You'd write a Gcode program to
"visit" the points of interest, and do a "probe cycle".

MaxNC does a G61, but doesn't STORE the data, as far as I can figure
out. I've been able to do it in some code I've been working on. So I'm
thinking something like a drill cycle could work to take samples on a
grid. Trouble is, ALL moves of the probe need to be "linear sense",
otherwise you could run into a vertical surface. That's what I'm
discovering!

I've been able to implement drill cycles, but I've never seen a "probe
cycle". It could be, as mentioned, like a drill cycle, but that would
only be good for a measurement in Z. We'd need everything to be "sense"
moves.

Yes, seems you need to go slow. I worked out sampling within a
trapezoidal acceleration/dceleration profile, but trouble is, depending
on the compliance of the probe, you could overrun it! Not good. :>(

Alan KM6VV


Jim Montgomery wrote:

>
> Hello all,
>
> I once got to watch a master machinist in a major plastics factory
> digitize a dodge hood ornament on a very large Milltronics gantry
> mill. I think the software was MasterCam but, I'm not sure. He was
> able to specify his own XY grid pattern and even arcs, curves and
> circles. Also, he could specify islands as to miss vertical walls
> and pockets. I do know that he tried different default grid scanning
> patterns before having to write his own to get the desired result.
> It made a difference in performance if the probe was falling off or
> climbing up the Z axis. For anyone writing a program I think being
> able to specify the path of the scan would be important. The machine
> hardware and software was all big name and big $ and still quite
> slow. If the object you are digitizing has large flat areas of
> easily measurable surfaces there would be a great time savings if
> you could omit that area in the scan and just add it by hand with
> your favorite CAD program. This might be a dumb example but, say
> your scanning an ash tray with a very detailed outer rim but the
> bottom is just plain flat.
>
> Sorry I can't be more exact about the software and probe, I was
> there to wire a new warehouse and didn't have enough time to soak
> everything in. I will stop by and tell him about the CAD_CAM_EDM_DRO
> list and invite him to join.
>
> Jim
>
> --- In CAD_CAM_EDM_DRO@y..., ccs@m... wrote:
> >
> > Anyone have plans or ideas for an inexpensive shop-built contact
> probe?
> >
> > I keep being amazed by cheap import indicators (plunger and lever
> > style) and being tempted to try to detect the needle position
> > optically. Say put a thin sheet metal flag on the needle that will
> > block a photointerrupter like used for home switches... or even
> put a
> > rotary encoder wheel on the indicator.
> >
> > Chris
>
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