Thanks for the thorough reply Craig, that all makes sense. I guess a question that comes to mind is, why did setting Mach 3 priority to real time seem to fix the uc100 sync error?  It was happening pretty much like clockwork, then after making that adjustment we performed hours of passes with no issue.

Hi,
I suspect that by elevating the priority of Mach3 that it suffers less interruptions and therefore the UC100, or rather, the USB connection
to the UC100 runs better.

As a side note Windows makes such extensive use of the CPUs interrupt system that it cannot ever be 'realtime'.
It is this lack of realtime determinism that prevents Windows/Mach from being a feedback controller, Mach, in fact all
Windows based CNC software solutions, must be 'buffered'.

Compare that to LinuxCNC, it runs on a realtime capable distro of Linux and it can creditably be a feedback controller.

Craig

Update:  I bought a Warp9 Tech Design Ethernet Smooth Stepper.  Connection was a breeze due to their awesome installation and setup wizard!! What a nice change from just getting a part in a box and having to figure it all out on your own.

Once I got it up and running, I ran into a hiccup in the first 15-20 inches of manual travel.  I got an "ESS ran out of data" error message, along with a link to the warp9 site where the solution for the problem is.  I reinstalled the driver for my ethernet port, and increased mach 3 priority to "high" and began a 3 hour facing operating on our new one piece HPDE vacuum manifold spoil board we are making.  The CNC completed the entire operating successfully without any errors!!  That is the first time we have had on operation that long run without a controller sync error of some sort.  Hopefully it will continue to work well.  Thanks for the support and suggestions, I'm sure I will be here fairly often with more.