Below are the last few lines of a roughing pass from last night. All went well til the 3rd to last line did not seem to execute and hence it drove the bit straight across my piece at full speed. More firewood I guess. Can anyone see anything wrong with this? I’m running the standard dual endstop marlin firmware on a Rambo 1.4.
G01 X370.546 Y136.435 F1000.0
G01 X370.561 Y160.308 F1000.0
G00 Z12 F480 <<<<<<<<<<<<<<THIS IS THE LINE THAT GOT ME
G00 X0 Y0 F3200
M05
In Marlin, G0 just shortcuts to G1, so that shouldn’t be a problem.
G0 Z12 moves the Z axis down 12mm, which is an awful lot of depth to try cutting at one time. What is your DOC set to?
That line of Gcode should work in marlin. My brain is circling around two possible reasons for the failure. #1 (software) somehow your machine thought that Z12 was lower than you expected. There could be a few reasons for this. Or #2 (Mechanical) your machine tried to lift the Z up and something went wrong.
I would test mechanical failure first. With the spindle off try moving the Z up and down. Test holding onto it to give the machine a little resistance. See if something is loose like the Leadscrew coupling or a Z motor wire.
If all of that works well then we can look into more of the Gcode to see if it did something to confuse the Z position. Like relative vs absolute positioning, or more likely an offset.
Z12 should be up to 12mm above the work, right?
Yes Z12 should have been 12 above zero. On my setup with zero at top of work piece negative z values are cutting (in my understanding). Any positive Z should technically be safe. Prior to the given code above it should have been at Z-6 (snippet below), which for the stacked text sign is the second layer (so a 3mm DOC at the time).
I checked the mechanics and everything was moving fine afterwards (both powered via lcd and by hand). I happened to be sitting right in front of the machine when it was running doing some other work and didn’t notice any weird noises (like the z skipping steps), but it happened fast so I may have missed it.
I think I will just chalk it up to an alpha particle from outer space and re-run it.
G01 X306.384 Y38.605 F1000.0
G01 X307.049 Y38.509 F1000.0
G01 X307.712 Y38.604 F1000.0
G01 Z-1.412 F300.0
G00 X304.358 Y25.391 F3200
G01 Z-6.000 F300.0
G01 X301.377 Y26.126 F1000.0
G01 X300.540 Y26.488 F1000.0
G01 X300.005 Y26.194 F1000.0
G01 X297.635 Y25.489 F1000.0
Yeah, I don’t see anything wrong with those couple of lines. Maybe a loose wire could cause it to lose steps. Or a loose coupler.
Last time I saw this happen it was the coupler. They showed a video where Z worked to push down but not pull up. In the video we could see the motor spin but the lead crew did not. So Z didn’t lift.
Z coupler all good. Ran a different job and all was good. I’ll keep an eye though if it happens again. Thanks for all the helps.
Anytime I’ve had this happen, it’s always been mechanical. It might only be a once in a while type blip, but it happens.
I’ve had a dozen different reasons cause it. Z stepper driver over heated once. Coupler slipped once. Bit fell out once.