Gantry crashing into bed after print

Question

I've upgraded my Ender 3 Pro to the point where I'm causing myself problems, one of them specifically is this:

My z axis drops down to the bed because of all the stuff hanging off it (added a bltouch probe, cable chain) whenever it is idle, example video of what I am talking about. When it first started happening I bought an Anti backlash leadscrew nut and installed that and it helped A BIT. The gantry wouldn't drop as often or as far.
But it still happens. I've thought about possibly adding a dual z axis motor and leadscrew anyway (with additional anti-backlash nut), and I wonder if that'll help because the gantry would have to overcome the friction on both sides..... but in the meantime I want to solve a very specific problem it causes: I just printed a benchy and right after the print was done (when I wasn't paying attention and before I noticed) the nozzle crashed right down into the print. It must have still been a little hot because it melted right into it. Not far enough to ruin it but I could see this causing an issue if it was something besides the Benchy.

Is there code I can run at the end of a print to tell the hot end to move out of the way? So if it does come crashing down its off in the corner or something? I use Cura and marlin if thats relevant. I did see this question but I guess my even dumber question is: if that code works, how do I add it? Is that in Cura?

Answer 1

What you describe sounds more like a last-layer (or near-last-layer) machine restart than a problem with the Z axis back-driving (though it shouldn't back-drive from the weight of the gantry alone; you may need to tighten things like the anti-backlash nut or Z rollers).

My Ender 3 has, a few times, restarted after 3-6 hours of printing -- leaving the nozzle in a lump of plastic that has oozed as it cooled, and the "resume or stop" selection on the LCD. I haven't seen any indication of overheating, excessive current draw, or other issues with any of my (box stock) components. I have ordered a small 300W UPS to let my machine ignore the (presumed) tiny power flickers that I believe are resetting my mainboard -- but I won't know for certain if this solves the problem for a few weeks after I get the UPS, because the problem has been sporadic even with overnight and longer print times.

With your upgraded mainboard and using the firmware provided by that supplier, you may no longer have the resume feature that was standard on my Ender 3, nor the end of print park (which, in any case, would not happen in the case of a machine reset).