Last night I experienced a problem with my machine, which I have been unable to determine for certain whether or not it is a mechanical problem, or electrical.
I started a MeshCAM carving, which completed the roughing cut without problems. I changed the tool to the finishing cutter, and continued with the finishing cut.
That is when the problems began. For some reason, the X axis started either losing steps, or failed to move as far as it was commanded to. This resulted in the piece being ruined. I stopped the machine, and returned all axis to zero to verify that it was correct. Sure enough, it was off by about 0.170" on the x axis. I re-homed the machine, returned all axis to zero (and it was then in the correct position).
I then entered the correct line number (following the tool change to the finishing cutter) and selected Run From Here, to continue the finishing cut. I could hear the X axis motor make unusual sounds occassionally during it's movement. As I observed the movement, the x axis seemed to be losing steps progressively, with each pass. It is important to note, that this machine has been in operation for a few years now, doing similar cuts without any problems.
Anyway, my point here, is to request someone to "Jog my Memory" on which utility it is in the Mach3 folder to test the pulse rate of the computer. As I simply cannot recall what the program's name is called. My problem may simply be that the threads of the lead screw nut have become so worn, that an excessive amount of backlash has now been introduced. However, the strange sounds coming from the x axis motor occassionally, is what makes me suspect that it may be a pulse problem. I just wanted to run that program, and watch it to see if there are any sudden changes which may be the actual problem. (And don't remember it's name)

DriverTest.exe? Is that what you are referring to?

  Is this correct? You said " I re-homed the machine, returned all axis to zero (and it was then in the correct position). How could you tell the machine was in the correct position after rehoming and returning all axis to 0?

  How has this machine been maintained? Might be a good time for cleaning, inspection and adjustment.

Something important when doing the 3d stuff is that the motors are capable of the accelerations required for the many short axis moves.
This can lead to missing steps, which may not be repeatable, is random in nature, is really hard to isolate, or make sense of.

Even though for a number of "years" all the 2d  machining  never had a problem with missing steps, it showed it's ugly head upon doing 3d stuff.

All the conventional checks and adjustments one would do just didn't help.

Upgraded the motors  and problem went away.

So, yes fine tune / adjust the machine, and try different motor settings just to be sure that there is no apparent problem.

FWIW,
Rich 

Thanks, Rich-
I found the problem- it was a software problem. I had installed MeshCAM version 4 on my shop computer, however when it prompted for the registration code (I didn't have it with me, at the time) a message popped up that I was using an un-registered copy (which defaults to only creating toolpaths for the included sample files). However, I went ahead and used it with my own file. It seemed to work just fine, all the way up to the tool change for the finishing cut. Perhaps Robert wrote the program to discourage unregistered users, since the rough cut worked great. (I don't know for sure, if it was intentional, but if so -Absolute Genius strategy to safeguard against software piracy). It was only on the finishing cut that things went awry.
I un-installed version 4, found my registration code, and re-installed it. No further problems.