My control is an Anilam Crusader II but this could work on other Servo control systems.
A few years back I saw a Microcontroller chip on the internet that allowed you to use step and direction with a servo. It worked by mixing the encoder feedback with step and direction. The chip would go between the encoder and the motor, a step command would make the controller think that the encoder incremented when it didn't. The controller would then correct for this and step the motor back to the commanded position. Basically, the controller would be trying to hold the servo motors still and the step and direction inputs would be electronically moving the encoder signal.
Anyway, my thought is to buy the connectors and cables to intercept the encoder signal. Have a PC with running software with step and direction outputs to control my mill while my Anilam Crusader II is trying to hold the axis's still. Since my Controller still works, this would be a much cheaper path to go than using a servo motion control board in the PC. I visited the website that used to sell the PIC microcontroller that was programmed for this type of application, it is no longer listed. I could program these chips myself for this application.
Anyone else interested in tinkering with this kind of stuff? (Upgrading older controls to PC Control)