Crashing in Z height

We have a Cincinnati machining centre with CNC Pro fitted, about 6 years ago. We have had a few issues with Z heights, but I had though we had overcome/worked round them.
Recently we have a new operator who has had a few crashes since joining us. I though it was him, until I took over, made a program which faced the top of a plate, going first to Z-0.75 mm, traversing in X, then to Z-1.5 mm before returning in X to original position. The first item I machined was fine. I put a second plate in the vice and pressed start, it machined the first cut, but then, instead of going to Z-1.5, it continued down, until the spindle head hit the plate. A distance of 150 mm, or more.
Does anyone have a clue as to how this could be? Surely if the distance traveled, does not equal the command there will be a fault and it should stop? I checked the encoder output on a scope and it is normal, just the same as the X & Y axis. Could some new interference noise be an issue, but again I would have thought that once it was going where it should not, it would fault? Could it have switched between absolute and relative distance to travel?

All help and pointers will be very gratefully received, as we can no longer trust the machine to go where commanded.

Regards, Colin

Add the command LOGOPEN SILENT to your startup.fil

This will write all sorts of detailed info to this file:
C:\AS3000\CNC\LOGFILE.FIL

Learn to quickly save this file anytime something happens. practice ahead of time. I have an icon on my desktop to save it to a different file name. THIS IS VERY IMPORTANT, the file is overwritten every time CYCLESTART is pressed

There is a huge amount of very detailed info in this file but you need to save it RIGHT WHEN THE MACHINE FAULTED.

I hope you are paid up with Camsoft support, the file is very hard to follow. I learned to do it but only after a lot of coaching from Camsoft.


Very likely you're looking for a hardware intermittent failure, the worse kind of problem. I keep an entire spare computer with all the boards ready to go. Then I can do a complete brain swap to see if the issue goes away.

Thanks Karl, no we have not paid up any maintenance, so I guess we will have to see if we can figure out something, if we can get it to do it again. Trouble is I can't run any jobs using expensive tools, or material, so basically I am writing programs with lots of Z moves, and letting it run with no tool, or anything to hit.

Do you think doing a back up and re-installing the computer might cure anything?

I am going in tomorrow to start running it, to see if it will do it again. I have a pile of work to do and have already sent a lot out to another company, at great expense.

Regards, Colin

You might get lucky by guessing.

If you really need it fixed, I'd hire an expert.

I do my own maintenance. First a complete spare computer with boards all set to go is required. Seeing if a different box does the same thing is important. Also learning to read that logfile is HUGE. Real good chance the machine just did what you told it to do, NOT what you wanted it to do. There's a difference.

I'm sure you know solving intermittent problems is the worst.