I appreciate your help.
I have the shield cable connected at both ends should I also disconnect one side inside the control box from power supply to the drivers . Just have the shield connected at the PSU end?
Also I have the shield connected at both ends from the driver to the breakout board should I also remove the shield connection at the breakout board and just have the connection at the drivers side?

What you using to controlit with Parallel port or some other motion control. I use a Parallel port.

What Control software andIf Mach3 what Kernal speed. The software is Mach3 and the Kernal speed is set at 25000Hz

What's MicroStep on drivesand Motor tuning settings for each axis. X axis Steps are 400.066 Velocity 1900.2
A axis Steps are 400.066 Velocity 1900.2

What PSU voltage PSU 400W 36 Volt / 11amp

What Make of BOB. Breakout board HG07

Stepper Motors 3.1 Nm

I will get another Parallel port cable to try as well.

The couplers to motorsare tight. And I also fitted a marker to see when It moves as I'm watching it all the time now but I can never be quick enough to stop breaking a end mill.

I hope you can see something wrong.