I have been fooling with this thing a lot today.
First, I tried to get the backlash out. Measuring by turning the steppers while using a dial indicator, I came up with the figures of ~0.0005 on the x axis, which makes me wonder if it needs to be loosened, and .007 on z. I programmed this stuff into the backlash area of Mach3 and enabled it, but I do not know whether the program is supposed to be started with the backlash taken up or left in for the PC to take out, so for all I know, I could be doubling my backlash error.
I switched to "Exact Stop" mode because I read that this was necessary to make backlash correction work.
I have two programs that do nothing but move an axis (x or z) back and forth by 0.5". I ran those and came to the conclusion that the best steps/unit for x as 81540. Over half an inch, this agrees with the indicator to within a thousandth. Z is now at 6580, after measuring. I can't explain it.
I can't tell if backlash correction is working on x, since the backlash is really too small to distinguish from my own error in reading the dial from two feet away.
I have not changed the output gain. It's still 1.
Kmotion has a backlash function, but to use it, I think I have to know the steps/unit figure, so I haven't tried to use it yet. Again, I don't know whether you take up the backlash before starting the program.
Update: I turned off the backlash correction in Mach3, and now I'm getting a consistent 0.499" when I ask for 0.500", in EITHER direction. None of this makes sense.