I have never had sort of problem with the probe signal, either using Mach via the parallel port or more recently a UC100 motion controller.  It sounds very much like a grounding issue, and you must have a very long distance between the ESS and the machine to need a 6ft wire.  That would imply long cables to the steppers too perhaps?

Not long at all.  I went to 4" when I tried the shielded wire.  The 6" unshielded works if I use just the wire.  It is being connected to the machine chassis that it doesn't like.  I only have about 12" from the ESS to the nearest chassis point.  I can try that, but whatever it is about the chassis that is causing the problem will still be there.

6"?  You said 6 ft in one of the first posts...

Oops! typo.  Yes, it was 6'.  There is nothing wrong with the wire.  It works over the 6' unless I connect the end of it to the chassis.  That does something to it.  I'm going to go out there an try putting a capacitor on the line.  That might settle any noise.

From what I recall the ESS inputs have a 4k7pullup to +5V.  If there's a lot of noise around that could be marginal.  A 470R resistor from the input to +5V may improve things though when the probe is grounded it will take 10mA from the supply which ought not to be a problem.

I have made some progress on this issue this morning.  My findings are interesting.  The original 6' ground wire I used was 16 gauge stranded copper.  This morning I decided that if ATZ worked at the ESS terminal end of that wire, but not at the machine chassis end, then somewhere between those two points something was happening to the signal.  So I grabbed a piece of 16 gauge solid bare copper from my copper scrap bucket and connected it from the ESS to the chassis at the closest point, which was about 12" away.  It worked.  I was able to stop the Z axis with the ATZ input wire at any point on the chassis.

Not being one to just quit at that point because I like to understand what the heck is happening, I continued my investigation.  I grabbed a 16 gauge stranded bare copper 1" long and tried it.  It worked.  I pulled 3 hair fine strands off it and tried that.  It worked.  I went back to the original 6" copper insulated wire.  Won't work.  I stripped insulation off 12" of it and tried that.  It worked.  I tried 6' of bare 16 gauge copper.  works up to about 4' then gets flaky and won't work at 6' or on the chassis.  Then I cut 12" off the original 6' wire and tried that.  It works.

So, my conclusion is that the ESS has to see as pure a ground as it can get to work.  The slightest resistance in the wire connecting its ground to the chassis keeps it from working.  Don't know why.  It shouldn't, but it does.  At least I can use the function now.

What I don't understand is why the ESS and Mach lock out the ATZ function if there is not a solid ground at the ESS input.  It won't work again until Mach is reset.

Thanks guys for all your input and suggestions!

I'm still having trouble with this function.  I can sit at the mill and try it three times and get three different results, only one of which is correct.  Sometimes it works right.  Sometimes it will stop the quill downward travel but not retract to the height specified in the visual basic file.  And other times it will not stop at all and I have to hit reset.  I all three cases, the digitize LED in diagnostics comes on.  At that point it should always execute all of the visual basic file, but it does not.

I have downloaded Mach 4 to see if it will work with that.  Hopefully the demo version will allow that function to work.  If it does, I will probably buy the hobby version because I could use the ability to run larger files than the free version of Mach 3 allows.

My question right now is, how do I port the Mach 4 demo over to my mill computer?  It is not all contained in an exec file like Mach 3 was.  I don't have internet on the mill computer so I can't use the online downloader.

Looks like Mach 4 hobby demo IS all in one file, so I think I'm all set.  I just put it on a flash drive and I'm taking it out to the mill to try installing it.  If it doesn't work, I will get back to you guys.