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Running Marlin 1.1.2, printing from Octoprint on Linux PC. So, the PC freezes up and I have to pause the print and reboot. It's a 36 hour print with 11 hours left to go and I'd rather not start over.

I have the X, Y, and Z coords of where I need to begin again, and I've deleted all the GCode to that point. In the several tutorials I read on how to resume a print, they all assume that the printer - which in my case had a restart of its own - knows where Z is. I can safely rehome X and Y, but when I try to rehome Z the print head moves to the center of the plate, which of course would cause a collision with the model.

On my printer the Z-axis switch is over to the side of the frame holding the print bed, so I can home Z with the print head anywhere. Is there a way I can home Z without the head moving to center? Or, barring that, some offset I can enter for Z so I can resume at the same height I started? I can't wrap my mind around what I need to do here.

Bill in Kansas City
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  • The PC should not freeze up, ever. If you really can't fix that, run octoprint on a dedicated rpi that you're not gaming or loading experimental kernel modules or whatever on. – R.. GitHub STOP HELPING ICE May 02 '20 at 19:56
  • It's actually a vanilla Kubuntu 18 PC whose only function is to manage the printer. This is the first time it's ever frozen mid-print and I think it's because I left Cura and several other Chrome tabs open. – Bill in Kansas City May 02 '20 at 20:22

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Was able to make it happen, though I fear that I may have misjudged exactly where zero was, but we'll see in a few hours.

Anyway, for those who may come along later, here's what I figured out:

I already knew what my X, Y, and Z positions should be.

I kept the heat on for the bed so the print wouldn't shrink and break loose.

With the plate lowered and the print well out of harm's way, I homed X and Y. Then moved X10 Y0, a convenient place to work.

I set relative positioning on, G91, and moved Z up toward the print head until a business card was firmly clamped between the head and the plate.

I then set Z at zero, G92 Z0. Apparently Marlin (or Octoprint? idk) will let you print without homing Z as long as it knows where zero is.

I moved to print head to my desired X, Y, and Z positions and checked it against the model, which seemed to be right. I fear that I may have not zero'd down enough, so there will be a noticeable gap/weak spot, but I won't know that until I get more layers on than there are at this moment. I suppose if that's true, then I could just shave off the new layers and reset zero a couple of layers tighter.

The rest of the steps for resuming a print (editing the G-Code and what-not) are readily available in a dozen or more tutorials, so I won't cover that here.

Follow-up: yep, left too much room. I shaved off the new layers (having a kiridashi really helped there) and re-zero'd, but this time, after doing so I entered my initial Z value so that the nozzle touched the model and adjusted from there. Note that aesthetics aren't an issue: these are mechanical parts to all they need is to not snap in the middle. Having a seam there isn't a problem.

Bill in Kansas City
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