Help newbie with coordinate system.

Dear friends, I have a new hobby CNC using linuxcnc. I'm starting to mill aluminum parts and of course my machine is very slow to do the jobs. Kress spindle, Nema 17...i spent a lot of time on it.

The machine have home switch and limits (the same for both). When I shut down the machine, if I do not want to lose work zero of piece (in my case, normally is in the center of the piece) when I shut down the machine. For now to me because I do not have edge finders, etc I'm having problems to make pieces because I have errors setting the work zero between jobs in the same piece but in differents days.

Is there any form to maintain or come back to the same work zero? Each time I restart the machine, I need to rehoming and I lose the zero points of 3 axis.

Also I want to know if I can use absolute coordinate to go zero machine and then go to the work zero knowing the machine coordinates of zero work piece before I shut down.

Thanks a lot.

Just create an empty file and name it "last_position.txt" and place it in the ~/linuxcnc/configs/yourconfigname.
Also add POSITION_FILE = last_position.txt to [traj] in the .ini file.
Even if the power goes off it remembers it's last position.

Thanks tommy for the fast answer!

I have a questions about the file.

It save the home switch positions, etc? Or i need to re home axis also??

If it is only for a some works, I need to modify the I I file to erase the positions??

Thanks!

It will remember the actual position the machine was stopped for whatever reason, even on power cuts. It will not remember the position of limit switches, just the position of axis. As far as i know, if you have reliable homing, that would be enough to reliably home again and again at the same position.
Example:
say it stopped at x100 y50 z25, start, home, send it to x100 y50 z25, it should go to the same exact spot it was stopped.

Give it a try, and report back.
Tom

Juanolo wrote: The machine have home switch and limits (the same for both). When I shut down the machine, if I do not want to lose work zero of piece (in my case, normally is in the center of the piece) when I shut down the machine. For now to me because I do not have edge finders, etc I'm having problems to make pieces because I have errors setting the work zero between jobs in the same piece but in differents days.

You seem to be saying that the machine has home switches?
If that is the case then you should be ale to power-up, re-home and just carry on as you were with no need to re-touch off or anything.

This does assume good repeatability of the home-switches. I do this quite often but my machines have absolute encoders so I am extremely confident about homing repeatabilty.

Hello!

The form I have learned is after I power on the machine is to home the machine then touch of the center of the piece and set to zero the G0 code. The problem is that the coordinate reset to 0 and it is difficult to set back to the same center I need to set again the work zero.

I do not know if when I home the machine, the absolute coordinates ? Set to zero? And if I write the G53 coordinates in a notepad, when I set the zero pice in G0 and restart the machine, can I come back manually to zero piece with the same G53 coordinates I wrote in notepad and it will be in the same position than before?

or another form is t play with g53 and g54 codes setting them to zero initially an write the values of g54 that are the same position as before ?

Thanks

Don't use G92 for this. Use one of the coordinate system offsets, such as G54.

Juanolo wrote: The machine have home switch and limits (the same for both). When I shut down the machine, if I do not want to lose work zero of piece (in my case, normally is in the center of the piece) when I shut down the machine. For now to me because I do not have edge finders, etc I'm having problems to make pieces because I have errors setting the work zero between jobs in the same piece but in differents days.

If you have home switches you should not lose your place. Normally Y0 is the front of the rear jaw and X0 is the left side of the material an Z0 is the top of the part. For X0 put a dowel in a holder and push the material up to it and lock the vise. Say you have a 1/4" dowel you then touch off X to -0.125, simple and fast to locate X. For Z use the same dowel and lower the cutting tool to lower than 1/4" and as you move the Z up when the dowel passes under touch off Z to 0.250" ( or mm if your using them). I use an edge finder for Y but you could use the dowel like Z to find Y and touch off.

JT