Essentially what the title states I want to raise and lower a sub spindle assembly on a mill head that uses two linear rails with 250mm ballscrew to raise and lower a 4kw sub spindle when machining above 6000rpm. I suspect I’d need some type of PWM control allowing I/O pins to trigger a stepper to run forward and reverse on a fixed 24v Supply controlled by limit switches. No positional feedback required here I just want to take advantage of a high torque braking stepper with built in 24v brake so when the spindle lowers 2.5” inches it is stopped by limit switch and brake engaged which will allow it to clear tooling in the bt40 spindle by an 1.25” inches. When spindle is lowered a output controlled relay will swap spindle from main vfd to sub vfd. This operation will lower and recess (raise) enough not to interfere with main spindle. My question is what is the best way to command this stepper without sacrificing any axis control and/or affecting ac servo performance of mill? I’ve been looking for ways to command a stepper driver by analog control. It would be nice if it was a simple process triggered by a single output pin off the BOB (control board) and it would also need to accept a command so it will rotate forward (down) or reverse (up). Either by a secondary output or when limit switch is triggered it sets the next command for opposing direction. I guess the issue is that I’ve searched and I don’t know of any available hardware or the best way to implement this process. I was thinking perhaps arduino may have a solution for this and someone here would know a specific application that can be applied without making it overtly extensive. This is easier achieved by using a 24v 2 wire motor and simple relay setup however I lose the torque holding of stepper with addition of added brake preventing the spindle from changing minuscule or wxcessive amounts of tool height by force and axial exertion from milling. Please share thoughts, ideas, or proven concepts. Thanks I’m advamce for your response.