Boley BKN 100 - Spindel as C-axis

Hi,
I´ve got a lathe with a DC Spindle drive that has an extra servo driver for milling operations. So the spindel would work as servo driven axis, let´s call it C-Axis. Simoreg 6RA26.
I´m not at that part yet, but i´d like to know before i start working on it, what´s best practice to implement that.
I´d like to have the spindel working as spindle with +-10V for RPM as a normal lathe and in milling mode it should switch to the servo driver, that works with +-10V too. I think i have a closed loop there too. Should i wire them up as if i had one physical spindle and one physical servo ?
So is Linux capable of switching mid program between the two modes ? is that a normal setup ?

It is capable to switch between the two modes but it is not a 'normal' setup.

Because there are different setups there isn't a 'one size fits all' solution to do this.
In your case I would wire the DC drive as the spindle and the servo as a rotary axis (eg 'C').
Solutions will largely depend on what kind of encoder signal(s) you have and whether those track spindle position at all times or only in either turning or milling modes.
If you have encoder and index feedback from the same source and the encoder position isn't lost when operating the the spindle at max speed then you can home the rotary on startup and don't need to rehome when switching from turning to milling. There is 'caxis.comp' to prevent the spindle unwinding the accumulated rotations for this case. The original version of this can be found in the zip folder in this thread:
forum.linuxcnc.org/10-advanced-configura...ling?start=50#288345

If you do need to rehome the rotary due to lost encoder position then make sure to take note of the bug described in this thread and the workaround presented:
forum.linuxcnc.org/38-general-linuxcnc-q...blem?start=20#324276