Add new axis

hi every one
I have installed Debian on a computer and i have a paralellport breakout board.
I am new in LinuxCNC.
Basic Installation and setup was done for a lathe.
2 axes are working.
I am using a servo motor in Velocity mode as a spindle motor, which is controlled by an Analog voltage.
The servo could be controlled in position mode (Step/Dir) and Velocity mode and i could switch between these with a Relay by setting a pin on the servo drive High or low.
I currently only have the servo wired in Velocity mode.
I would like to add C-axis capibilities, so i need to add a new axis.
I've tried watching some HAL Tutorials to try to understand it, but i find it very complicated.
Can someone help and show me how to add a new axis in the INI and HAL file?

Thank You
 

Sorry for the late reply and not helping, i have to leave the explanation to someone who is better at it.

Anonymous wrote:

The servo could be controlled in position mode (Step/Dir) and Velocity mode and i could switch between these with a Relay by setting a pin on the servo drive High or low.

Are you sure that the drive can switch between step-dirt position mode and velocity mode on the fly? 

If that is possible, then this should be much easier than is normally the case. 

You need to increase the number of axes to 3, and use coordinates=XZC in the INI (probably in two places) 

I strongly suggest an update to LinuxCNC 2.8.2, that should make it rather easier to configure a 3-axis XYC system. 
 

Yes i can switch between position and speed control on the fly, though if i do it when the spindle is still turning it will just decelerate verry fast and probably break stuff.
I tried implementing those changes but i couldn't get it running that way. Do i also have to add something to the hal file.
I have now run stepconf again and configured my machine as a milling machine and just changed the name of the Y-axis to the C-axis, I also changed all the Y characters in the hal file to C. It now works and i can run gcode with XZC values.
There is still some stuff that doesn't work correctly, for example the display shows the gcode in 3d space, but it should only show it in 2d space. The arrow keys also don't jog the axes correctly.
This is probably verry dum, but i don't know how else to configure it.

What do you have for [DISPLAY]GEOMETRY ?