Mill with auxilarry spindle

I have a three axis gantry router using stepper motors on the three axes and wish to use the A output to drive an auxiliary spindle through a stepper motor. The router spindle is driven through a VFD.
I need the auxiliary spindle to run at a controlable steady rpm (and also be controlled by at variable speed through the g-code if possible).
The machine would then run as a router lathe.
Despite searching i can't find anything that indicates how to set up STEPCONF for this purpose or how to drive the stepper.
Is it possible to use a stepper motor for this and if so how do i do it?
The nearest i got to understnding it was
Help will be much appreciated.

If you just need a step rate and direction set by a gcode command its
certainly possible in the hal file but I dont think the stepconf knows how
to do this.

Basically you set up a new step generator running in velocity mode
and connect the stepgens velocity command to perhaps a analog output pin
set by a M68 gcode

You don't need to use M68 as Versions 2.8 and 2.9 support multispindle configurations.
So you can control the speed using M3, M4 and S commands but you will still need PCW's methodology to set stepper speed.

See:
linuxcnc.org/docs/devel/html/gcode/other...ec:set-spindle-speed
linuxcnc.org/docs/devel/html/gcode/m-code.html#mcode:m3-m4-m5

You should be able to use some hal logic on the spindle forward and reverse pins to map to a step direction signal. See
linuxcnc.org/docs/devel/html/man/man9/mo....html#SPINDLE%20PINS
off the top of my head an or2 on the direction pins with the output and2'd with one of the original direction pins should do it.

So its time to learn how to edit your hal file by hand.

You should not need any special direction pin mapping, just use the signed spindle
RPM from LinuxCNC, for example spindle.1.speed-out, and connect it to the stepgen
velocity command, direction will then be automatic.

Thanks for your replies which I'm sure will help. I won't be able to get to work on the issue for a while but I'll keep you posted.

Nice set up. Who was the mill manufacturer?
MArk