Thank you for the advices and answers. I really appreciate your comments.

There is a lot to be considered and since I have no experinece with closed loop steppers or servo, I really don't know why a weaker servo is more expensive than a stronger closed loop stepper.

I had a closer look at this one: https://www.omc-stepperonline.com/in...rvo-motor.html

It is very similar to the one recommended by Jazz, bur it is a Stepperonline version. There is though one difference which immediately is obvious, that is the the Stepperonline version has no enable signal. It is not clear to me when the motor is enabled and when not. I mean, I am actually using the enable signal, and I want to be able to disable it so that I can manually rotate the spindle if I want to, without having to power off everything. It is not clear to me how that can be done unless there is an enable signal. It is also not very clear to me if this is a 3-phase servo or not. The one in Dean's link looks like a 3-phase motor.

But there is another question... that is about the torque. Both Dean's, and the one here have considerably less torque than 4Nm... so would a closed loop stepper with 4Nm be equal to these two...? I mean, high rpm and smooth, quiet running is one thing and is very nice, but if it is at the expense of less torque then I don't see the benefits. I need this motor to be able to hold the chuck when I use it as a rotary axis, not just rotating fast. So what's the secret? Can these servos be used as ordinary rotation axis steppers also, and can they hold the position when used on the CNC mill?