Mill with auxilarry spindle

Pin 'stepgen.3.position-cmd' does not exist 4677

That isn't surprising that it would not load. When you change a stepgen from position to velocity mode, it changes what the pin names are for that stepgen. So the pin named stepgen.3.position-cmd no longer existed causing a hal file error and Linuxcnc not to start.

Thanks again for your reply and as you can guess my knowledge of these things is woefully inadequate; please bear with me. I studied the HAL tutorial last night and am now a little wiser but not wise enough.
I found another Linux post, "4th Axis rotational angle limit problem" where the issue was similar to mine and changed the hal file in a similar way but without success.
I attach the modified hal file.
If you can help i would be grateful.

Doesn't look like the file got attached. Also the debug message was 'axis.3.motor-vel-cmd' does not exist.

I added, "net avel-fb axis.3.motor-vel-fb => axis.3.motor-vel-fb" to the hal file and the resulting debug message was:-
./ Mill-Lathe.hal.103: Pin 'axis.3.motor-vel-cmd' does not exist 4004.
The hal file is attached.

That is because that pin does not in fact exist
There is a pin axis.N.joint-vel-cmd. (but not a motor version)

Thanks again.
I modified the hal file in line with the post i mentioned earlier and Linuxcnc now opens. With the settings i had for position control i get the error, " joint 3 following error. I've played around with the max velocity and acceleration as well as ferror and min ferror without success. I've tried using m3s1000 to no avail.
I've also tried changing Axis 3 in the ini file that suggested in the above post again without success. The change was to delete the Axis 3 element and replace it with:-
[AXIS_3]
STEPGEN_MAXACCEL = 1125.0
SCALE = 100
I've reduced these two parameters; no joy.
I'm sailing round in a sea of uncertainty and perhaps the problem still lies in the hal file!

To combine both position mode (for A Axis use) and velocity mode (for spindle use)
is fairly complicated. I think it can be done with one stepgen in velocity mode
but requires a PID component and a bunch of signal re-routing depending on mode
plus dealing with the following error issue.

With software stepping, I suspect the simplest way would be to
have two stepgens (adding one to your existing configuration) ,
one setup in normal position mode for the A axis and one setup in velocity
mode for spindle use.

Then whatever signal you use for changing modes routes either the A axis
step/dir pins or the spindle step/dir pins to the physical parallel port pins
using either a mux_generic or a couple of lut5 components in hal to select which
stepgens step/dir pins get routed to the hal parallel port pins that drive the A axis/spindle.

If you dont need A axis gcode at all but just a variable speed, its much simpler .
You would just delete all the A Axis setup in your ini file and connections in you hal
file and just set the spindle velocity in the gcode.