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ok see attached file
i have left gaps to show the parts modified etc .

notice the specific gcode turning off work offsets and setting modes , this is good practice to essentialy set up the machine rather than presume that the machine is correct
at the top of each gcode file and resetting at the end etc .

it also sets tool to be specificly tool 1 etc , i always leave tool 1 to have no offsets in my tool table , so i always have a default

i show this as an example , i'm not saying it's error proof , so check before using etc This attachment is hidden for guests. Please log in or register to see it.

Bullseye wrote:
I suspect that you are in relative motion (G91) mode, by mistake. It might be that all you need is a G90 command
www.linuxcnc.org/docview/html/gcode/gcode.html#sec:G90-G91

You could possibly set this in the MDI window, and it ought to stick, but it is good practice to set it at the beginning of all programs to be sure.

Another possibility is that you are losing position during a long rapid. This will only happen if the machine speed/accel are set too high though.

in either of the above case Machine -> unhome all / followed by a re-home ought to fix the issue temporarily. If it is a machine-offset being applied, then it won't/

Bullseye wrote:
But you didn't specify absolute in your missing preamble. Also G53 with axis words without a motion word will do nothing. You would have to say "G53 G0 X0 Y0 Z0" to rapid to the machine origin. Notice the G0 rapid word in there.

Your file only contains G0 and G1 moves and I ran it twice in the simulator and don't see anything shifting on the second run so I agree the problem has to be elsewhere.

I have been working on a G code tutorial specifically for LinuxCNC, if you care to look at it the preamble section it will help you prepare a proper preamble for your G code.

One last note the normal file end it M2, I'm not sure what M30 does exactly...

Also, have you tested your machine to make sure your not loosing steps?

linuxcnc.org/docview/html/common/Stepper...ostics.html#_testing

John

John :
M2 is End program (usualy with reset , no rewind )
M30 is End program ( always with reset and rewind )

so a slight variation John

sorry for hijacking the thread , but just to answer Johns query etc ..
good work on the gcode tutorial to

Thanks. I will try the modified code today and let you know how it worked for me. Can you explain how homing works when you do not have a dedicated home switch? Also, it seems that the homing process is more an assigning the current point to X0 Y0 Z0 than actually moving the tool to the desired point. I know that you typically want to accomplish both actions when you perform a home operation but no movement occurs unless you issue a G0 or G1 command right? I keep struggling with how (the correct way) to get the tool back to the home position accurately without having to manually touch off on each axis when I want to return to the home position. I know that these are pretty basic questions, but as good as the documentation is, I just cannot grasp this operation.

Bill

cncbasher wrote:
IIRC LinuxCNC does not have a reset or rewind and the docs suggest that M30 is to exchange pallets. I don't think M30 really does anything that I can see anywhere so better to use M2 with LinuxCNC.

Thanks, if you notice anything missing/wrong or needed on the tutorial let me know.

John