The SS is not the problem. The combination of spindle and cutter runout along with depth of cut makes
the individual cut lines run together such that there is no longer any space between them. Since the color
is lost ( visual spacing) you no longer have a legable letter. So the mechanical system becomes the limiting
factor and not the ability of the software and hardware.
If some fraction of a silly .0001" was added to or removed from a cut you would not see it. Which brings us
back to what we have been trying to say all along.
Now to see say 0.000100" you need to look at it under a lot of magnification. If you had a known optical
standard to compare to, ( yes i have one that goes to .000020" ) , took the time to calibrate a 1000x microscope in a controlled enviroment, along with proper lighting etc, then you can monitor the actual or non step mechanical movements to sent pulse for fractions of the silly .0001" inches. But in your case, why do all that since your resolution that you have for a step is .0001" and frankly, depending on your stepper motor the micro step won't exactly position in the electric field for that pulse. Of course you can try a different motor and would find out that they are not all created equaly and thus would find differences.
Let not the heart be troubled due to an emotional issue of display.
RICH