I built a machine that uses Mach3 and a parallel connected driver.
when tested with simple gcode commands everything works well, like making a series of concentric circles, all is very accurate and nice, no missing pulses, it is nice and round, and checking with a dial, accuracy is 0.02 - 0.03 mm.

Whoever when trying to run a complex gcode file (like PCB engraving), the program loses a "gap" like 5 mm or so, ( as if the coordinate system jumps to a new location), I have no idea where this is coming from.
One idea is that maybe the Mach 3 real time pulse is effected by some other program running in the background (I don't know which).

If anybody ever had such problem, I will be happy to lean about it at this point, I don't even know if its a hardware or a software problem.

Thanks