Using a step/dir servo for a spindle

I am looking into using a 2Kw servo motor and drive that accepts step/dir inputs as a spindle on my converted CNC milling machine. I am currently running LinuxCNC but without spindle control. My ultimate goals are as follows:

1. install the motor/drive and get it so I can control RPM and direction. I have researched this and seems like I would add the servo as another axis and set the axis for velocity mode. I found some information that I think i can follow to achieve this. This would be my first step.

2. Get the system working well enough that I could use it for tapping. Rigid tapping would be great but tapping with a tension/compression tap holder would be fine too. I'm thinking if I get #1 working that this one might work straight away. Is this correct?

3. Final goal would be to be able to rotate the spindle to the index position of the encoder and stop there for tool changing. This would be way off, and to be quite honest is something I might not even get to but hope to some day. I have no idea how this would be implemented.

Any suggestions on any of the above steps would be great.

Thank You in advance.

I rigid tap on my BP knee mill by adding an encoder and a drive braking resistor. I use an Automation Direct GS2 drive that LinuxCNC controls just fine. Might be an easier path to travel...

JT

109jb wrote: 1. install the motor/drive and get it so I can control RPM and direction. I have researched this and seems like I would add the servo as another axis and set the axis for velocity mode.

I don't think that this s quite right. You would configure the spindle as a spindle, and connect the spindle-speed command to a velocity-mode stepgen.

2. Get the system working well enough that I could use it for tapping. Rigid tapping would be great but tapping with a tension/compression tap holder would be fine too. I'm thinking if I get #1 working that this one might work straight away. Is this correct?

You don't actually need angular control of the spindle for rigid tapping, LinuxCNC just needs to be able to control speed and direction, and to have access to the encoder position feedback. So yes, if you have 1, then rigid tapping is just a case of connecting the encoders in HAL.

3. Final goal would be to be able to rotate the spindle to the index position of the encoder and stop there for tool changing. This would be way off, and to be quite honest is something I might not even get to but hope to some day. I have no idea how this would be implemented.

With a velocity-mode stepgen you would need to add a PID controller to do the absolute positioning. You could, in theory, use the servo step/dir control but that means swapping to a position-mode stepgen somehow (You can't change mode on the fly)