I'm using a Creality Ender 3 V2 with BLTouch and Smith3D Marlin firmware.

Yesterday I designed a speaker adapter ring for my car in Autodesk Inventor. I converted the part to OBJ and sliced it in Cura. It was a fairly simple circular-shaped part that would normally not cause any issues.

The first layers went on great, did not expect it to go bad at all. When I woke up this morning, I found my print bed on the floor, luckily still in one piece, with the part still glued on. The clips holding the bed down flew off, and my BLTouch broke clean off.

I checked the part for warping, but it was straight as an arrow. I checked for burn marks, none. I couldn't find the area of impact either, probably because the BLTouch took most of the impact and flexed a bit.

I checked the Cura slice for weird motions but there didn't seem anything wrong.

What could have caused this? The printer was hours into the print when it happened.

The only thing I can think of is that Cura somehow incorporated bad G-code causing the Z-axis to move halfway through the print.

Any input is greatly appreciated. I don't quite trust my printer anymore.

I think we can safely assume that the print head moved down on its own. I live alone without any pets. Harry the house mosquito, albeit extremely annoying, is probably incapable of pushing the print bed off. The pushpin wouldn't be remotely strong enough, and the BLTouch mount snapped in half as well, so there was a lot of force applied here.

Would cosmic rays actually be able to cause this?

Nothing was connected via USB. So that leaves 2 and 3. I ran a clean version of Cura, that I always update, so it should be at the latest version available as of September 6th.

As soon as I find the time, I'll swap out the BLTouch or revert back to the stock one until new pushpins arrive. I'll probably try out a fresh slice from Cura and hope for the best I guess.


1 Answer 1


Assuming that we know one thing for sure, we can identify 3 possible causes:

  1. The print-head moved down
  2. The BLTouch lowered its pushpin
  3. Some external factor pushed the bed off
  4. Cosmic rays could have caused a bit to flip

Assuming you kept your Ender 3 in Marlin flavour, the print head could have moved down in 4 possible ways:

  1. something connected to USB sent a G-code signal
  2. the printer inserted a G-code signal (very improbable that a printer sends self-destruct signals)
  3. Cura inserted something into the code. Cura plugins sometimes add G-code that might not be visible in the preview. You can also rule this option out by printing from the same file from the same SD card again.

I don't know if the pushpin of the BLTouch is strong enough to break the BLTouch. Does it show any strain from sideways force?

Do you have cats? Dogs? Birds? Kids?

If a bit in the RAM of the AVR controller is flipped, it could for example, move the print-head down instead of up. This is very rare, but it does happen occasionally and cause big problems.

  • $\begingroup$ the NOAA Space Weather Prediction Center doesn't indicate any appreciable activity over the last 24h so probably the first three. $\endgroup$ Oct 9, 2021 at 16:05

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