Look at the Config menu then ToolTable and see if you have a height offset for Tool 1
It could be that you are starting off and zeroing the axis with Tool 0 loaded and when your code calls Tool 1 the height offset is applied.


Hood

Thank you for you kind donation of your experience. and offering your suggestion, I will try that... I know this is a dumb question, but those are all on Mach 3 right?

Yes, config menu in Mach and then tooltable, see screenshot. Also when you first start Mach see what tool number is showing, again see screenshot.
Hood

A few questions -

Is there a g41 or G42  ahead of the line where this happens? I have had a couple times where I got strange results because of something not quite right when I used Cutter Left/Right. Not lately, not sure whether the problem is gone, or I am just writing better gcode...

Have you tried going to the toolpath screen and hitting Simul;ate Run - I have had a few times where this cleaned up the display and made things run better.

Is this on the first run of the day? If the machine was not in a good position when you started you might want to move it to a good area in the middle of travel and then exit and restart Mach3.

Can you post the code so we can see what it looks like?

Does the Z display show agree that the cutter is way below zero or is it at some bizarre position? Could be you are starting with bad values in one of the g54 through g59 settings. Check the offsets page and make sure there are no odd numbers there before you start. ( a set of MDI lines with G90 for the first one, and then G92 X0 Y0 Z0 can clean them up, just resets the current position to 0,0,0)

The reason I ask a bunch of questions is not that I am a Mach3 Guru, but because the biggest problem with diagnosing a problem is a lack of details so everyone makes a bunch of guesses and they may or may not provide any benefit.

My guess is that it's being caused by G43. The Standard Vectic Mach3 posts insert a G43, and I've seen this happen due to that. I use a modified post with no G43.

As for G41/G42, I use them for everything, and have never seen them cause an unwanted Z axis move in years of use.

Thanks for all the great questions.

********Is there a g41 or G42  ahead of the line where this happens?
It always happens the same time. When I start Mach 3, I start the code, it runs a few lines, then stops, then I hit start again and then it drives through the material.

*******Have you tried going to the toolpath screen and hitting Simul;ate Run
No I have not, I didn't know this was something that I could do, so I will try it.

*******Is this on the first run of the day?
Now that you mention it, It is almost alway on the first run of the day. can you tell me more about that process in a step by step please,I am not sure i completely understand.

******************Can you post the code so we can see what it looks like?
It has happened on all kinds of code, but I will attach the last inlay I was doing. I don't think it was the code, because after doing it, I used the same code to cut the perfect inlay.

***********Does the Z display show agree that the cutter is way below zero or is it at some bizarre position? When I start it says 0, but when it bores, it says that it is +60 sometimes.

The reason I ask a bunch of questions is not that I am a Mach3 Guru, but because the biggest problem with diagnosing a problem is a lack of details so everyone makes a bunch of guesses and they may or may not provide any benefit.