need a linuxcnc with 4 linear axis for 3d printing

I have been running linuxcnc for about a year as a 3d printer driver. I have used the rotary A axis for the extruder and configured it to work but not without issues. My "work arounds" are not cutting it anymore as my printed parts are getting larger. I now have a problem with not being able to zero out the A axis when I start a new print. I have seen where others have been able to get linuxcnc to have the 4th axis be linear but I am still stuck with a rotary 4th axis. Could some one please help me? I am using a xylotex stepper driver system, (open loop steppers). Hopefully somebody already has what I need and can send or point me to an easy load or install type solution. Thank you for any help with this.

What do you mean you cannot zero out the A-Axis? Do you mean you cannot home it, or you cannot get the display to read 0 degrees?

Couldn't you use a match mark and home to that, or am I not understanding your problem?

Joe

I notice some people have dispensed with the idea of a motion axis
for the extruder and instead use the print head velocity:

basdebruijn.com/2014/05/machinekit-and-additive-manufacturing/

To me this seems like a better way to go

I can home the machine and it will show on the preview display that the A axis is at zero. When I try to start a new print it starts my A axis runnng backwards. I guess the rotary axis is trying to move back to what it thinks is zero. I have tried using G92 A0 to fix this but I have found that this does not work with very large prints with gcodes of about 8meg or bigger. 3D printer gcodes can be very large.

I saw this page before but I really want to not have to change the slic3r data. Really what I need is the XYZ and A axis to all be linear. If I can get that I believe linuxcnc would be much better for driving my 3D printer.