Can someone help me understand what's on this preview screen?

I put an arrow pointing to the circle thingy on my LinuxCNC preview screen. I can see that the circle's center seems to correspond to the G54 X and Z coordinates. What I don't understand is why it's set there (X=0.557 and Z=0.000) and what purpose it serves.

I used Ezilathe to create this g-code program for my lathe. Some screenshots are attached. I'm still very new to this Ezilathe software, and this part is my first trial in learning to use LinuxCNC on a lathe.  

The round thing that looks like the NATO sign?
It shows that there are active offsets, have a read here:
linuxcnc.org/docs/html/gcode/coordinates.html

Another note I forgot to mention is my lathe has no physical limit switch for homing. So I set up reasonable travel limits in my ini file. I manually home each axis a safe distance away from the work piece, but not so far away that it would exceed the soft travel limits.

For this kind of set up, is there a particular coordinate system that is most suitable?

I had and still maintain machines with no limit switches, once you learn to live with it, it works just fine.
And i use g54 on those, always.
But i have little experience with CNC lathes, so might want to wait for someone more experienced to answer.

usert_l wrote:

I put an arrow pointing to the circle thingy on my LinuxCNC preview screen. 

After a bit of experimenting, I think that it might be the machine absolute zero. 



 

andypugh wrote:

usert_l wrote:

I put an arrow pointing to the circle thingy on my LinuxCNC preview screen. 

After a bit of experimenting, I think that it might be the machine absolute zero. 

 


Ironically this came up tonight with regard to QtPlasmaC, and after some experimenting, I can confirm that Tommy is right, it does indicate that one of the various offsets is active (or not zero'd out).

That said, it seems finnicky. Example: I had a G54 and G55 offset set. I G53G0X0Y0Z0 and then touched off on all axes. Same for G55. The small origin (glcanon.py calls this "draw_small_origin") persisted. Restarted, and it went away.

But further, I'm not sure I understand the point. As soon as you touch off (G54 for example) the small origin will light up. It will remain always lit up unless you take the time to go to machine zero, and clear all offsets (and possibly restart). I'm having trouble picturing the work flow where this would make sense/be necessary?

In AXIS, you can have the inset DRO display machine position or user system position.
The origin only shows when displaying the user system position.

So it indicates what system you are looking at.

cmorley wrote:

In AXIS, you can have the inset DRO display machine position or user system position.
The origin only shows when displaying the user system position.

So it indicates what system you are looking at.

Interesting. I (and maybe Andy too) would have expected it be opposite of what you described. Meaning it shows when viewing machine coordinates.

Thanks for clarifying Chris.

To be clearer - the origin shows up in relative (user system) mode but it is displayed at the machine origin.
The XYZ marker arrows are at the user system origin.

Where as in absolute (machine system), no origin symbol, arrows at machine origin.

I like it, i can take a quick glance and see that machine 0 and material 0 are not the same, it reminds me to set material 0, i tend to forget that sometimes.