That’s an older machine running Mach3 via parallel port. If you are bugged, the best solution is to upgrade to a hardware motion controller. Right now, the computer is generating the step/direction pulses internally, via code, and transmitting them via parallels port. The parallel port is limited in how fast it can go, the 25khz or so, is that speed. At the same time, it is updating the screen and lots of other background things going on (polling keyboard, monitoring USB bus for mouse, etc.). That is why there is a slight amount of variation in timing, what you see as “glitching”. A hardware motion controller takes over that function and does it via a dedicated, real time hardware. Most are capable of faster pulse generation than the computer. The cheapest one is a uc100 (~$110). It connects to the computer via a USB port, and has a parallel port plug on the other end. It is capable of 100khz, and will work with your Mach3. I use one called an Ethernet SmoothStepper, it can generate 6 axis motion at 4Mhz (4,000,000 steps/second), you can also use it with Mach3 (I use Mach4 on my homebuilt machine, it is what Avid is now using on newer machines as well).
Mach3 is deprecated, has not been updated since 2012 (and never will be in future), has trouble with newer versions of windows, has a poor 3D planner and cv implementation compared to Mach4. But if you have it working, you can continue to use it, switching to a hardware motion controller will make it work more smoothly. But it is hard to recommend changing a system that is working to produce good parts.
Updating to a motion controller will allow you to use newer computers (most nowadays don’t even have parallel ports) and newer versions of Windows. I believe in having a dedicated computer as you do, and leaving it offline, with no updates, is ideal for a machine controller. But being able to easily replace the computer if it fails, without having to go through hoops to find and install an older, unsupported version of Windows also has advantages.
