Reset machine coordinates on special machine.

Tl; dr
Is there a way to reset the X and A- axis machine coordinates or re-home from G-code?
Assuming there is no way can someone point me to the right Part of the source code so I can  add a few lines and re-compile linuxcnc.
Or if there is a solution using nml that would be appreciated too.


Hello Everyone,

I have this quite unusual machine where the  material is fed by rollers(yellow). The  travel of X is "infinite".
After The Scissors cut off the material the machine is "homed" eg the X-axis should be at 0.0000


 
 

Linuxcnc assumes X has a fixed length in machine coordinates I guess
So I could not find a way to reset X without rewinding it which would push out the material as it has already been cut off.

G92 did nothing to the machine coordinates.
Using offsets G54 ... does not work either for my case as  this is a pretty fast machine that is being fed several G-code files a minute generated by another program.
The X value could exceed the variable size  in which it is stored.
Re-homing the machine manually just takes too long and can be forgotten doing it several times a minute.


Is there a way to reset the X and A- axis machine coordinates or re-home from G-code?

Assuming there is no way can someone point me to the right Part of the source code so I can  add a few lines and re-compile linuxcnc.

Or if there is a solution using nml that would be appreciated too.

Thank you in advance.
 

At the moment both A and X are homing immediately.

I simplified this machine a lot to make it easier to digest, a microswitch would not work.

However if tripping a microswitch while running gcode works then I should be able to use a M64 P1
from g-code and wire that output to the input of home x.

Sounds like a good compromise if it works.
If that works perhaps it is possible to include some while and if else to home X in the beginning of the gcode.

Will update as soon as I try it.

Not sure was the problem with g54 is. But G10 L20 P1 X0 A0 will set axis zero on actual position. 
P1 G54
P2 G55
….

@Chris and Andy
I read the docs before making this topic.

Let me clarify my concern again.

The spool is 100 000 mm long and several spools are changed during the day.
If keep offsetting using G54 the G53 coordinate would exceed 999 999.

This is a mess I would like to avoid .
The machine is not using fixtures, using G54 G55... makes things just more complicated.

The easiest and best option is to reset the G53 coordinate as soon as the material is cut.
Because the machine is really at X0 then.
Same with the pizza cutter, it has no limits after cutting it should be zeroed.

If I just could reset the G53 Variable this would solve everything.

Tommy, I tried your suggestion and it did not work.

Perhaps I did not really understand what you meant.
If I trip the home switch of x while running a gcode file, that does not reset the machine coordinates(G53).

I'm using trivkins with 2 gantrys so both=true , and yes I did check the home-switch is working properly using hal config viewer.

No, every piece is different.