<p>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).</p>
<p>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 &quot;resume or stop&quot; 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.</p>
<p>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).</p>

CC BY-SA 4.0
2021-06-03T17:21:28.953Z
Who knows if I should have officially "accepted" this answer until I try it all, but very helpful info so I went with it.  I'll check my firmware for both the "parking" and the resume feature (it didn't say anything like that on the screen, it just said 'ready', but again, maybe that was not in the firmware.
Joseph Crozier
CC BY-SA 4.0
2021-06-03T16:51:55.583Z
2021-06-03T16:51:55.583Z
Zeiss Ikon
<p>I've upgraded my Ender 3 Pro to the point where I'm causing myself problems, one of them specifically is this:</p>
<p>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, <a href="https://www.youtube.com/watch?v=Lpc1bTsSpRA" rel="nofollow noreferrer">example video of what I am talking about</a>.  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.<br />
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.</p>
<p>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 <a href="https://3dprinting.stackexchange.com/questions/5527/any-code-to-move-up-z-axis-after-finishing-the-printing">did see this question</a>  but I guess my even dumber question is:  if that code works, how do I add it?  Is that in Cura?</p>

CC BY-SA 4.0
2021-06-03T16:34:41.817Z
To clarify -- your gantry is heavy enough to back-drive the Z screw when the steppers are disabled?  And the only thing you've added (that weighs anything) is the BL-Touch sensor and its mount?  FWIW, my Ender 3 raises Z about 10 mm and then parks to min-X and max-Y at end of print.  Yours doesn't?
Zeiss Ikon
CC BY-SA 4.0
2021-06-03T16:38:42.083Z
@ZeissIkon  I BELIEVE that is accurately describing whats happening.  I never saw the gantry slide down when idle until I installed the bltouch.  For instance (now) if I turn it on, wait a second or two and then just breathe on the gantry or flick it or something, it'll start sliding down.
As far as where it parks, I never really watched it after a print, but when I came in an noticed the nozzle on the benchy, the print looked done and there were no error messages.  It was just buried a mm into the top of the chimney
Joseph Crozier
CC BY-SA 4.0
2021-06-03T16:40:15.403Z
You've got a ball screw as your anti-backlash Z drive?  That alone makes it easier to back drive the Z screw.  What you describe sounds more like a last-layer machine reboot (mine has occasionally done this, I think due to power flickers too small to notice otherwise).
Zeiss Ikon
CC BY-SA 4.0
2021-06-03T16:40:35.607Z
@ZeissIkon  one other possible relevant change I made was that I swapped out the board for a BTT E3 RRF and installed their copy of marlin.  I suppose the "parking" at the end could be different now.  Is that somewhere in the firmware?
Joseph Crozier
CC BY-SA 4.0
2021-06-03T16:41:48.350Z
As far as the ballscrew question:   For the z drive it was just the stock ender 3 pro with the anti-backlash nut from that video I linked.
Joseph Crozier
CC BY-SA 4.0
2021-06-03T16:42:35.463Z
I think the parking is in firmware, but I can't picture why you'd park above the new part instead of clearing the hot end and gantry and then pushing the part out front.
Zeiss Ikon
<g-code><z-axis>
Gantry crashing into bed after print
Joseph Crozier
# Gantry crashing into bed after print

(Asked by: username_0 on 2021-06-03)

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](https://www.youtube.com/watch?v=Lpc1bTsSpRA). 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](https://3dprinting.stackexchange.com/questions/5527/any-code-to-move-up-z-axis-after-finishing-the-printing) but I guess my even dumber question is: if that code works, how do I add it? Is that in Cura?

**Tags:** g-code, z-axis

> **Comments:**
> **username_1**: To clarify -- your gantry is heavy enough to back-drive the Z screw when the steppers are disabled?  And the only thing you've added (that weighs anything) is the BL-Touch sensor and its mount?  FWIW, my Ender 3 raises Z about 10 mm and then parks to min-X and max-Y at end of print.  Yours doesn't?  
> **username_0**: @username_1  I BELIEVE that is accurately describing whats happening.  I never saw the gantry slide down when idle until I installed the bltouch.  For instance (now) if I turn it on, wait a second or two and then just breathe on the gantry or flick it or something, it'll start sliding down. As far as where it parks, I never really watched it after a print, but when I came in an noticed the nozzle on the benchy, the print looked done and there were no error messages.  It was just buried a mm into the top of the chimney  
> **username_1**: You've got a ball screw as your anti-backlash Z drive?  That alone makes it easier to back drive the Z screw.  What you describe sounds more like a last-layer machine reboot (mine has occasionally done this, I think due to power flickers too small to notice otherwise).  
> **username_0**: @username_1  one other possible relevant change I made was that I swapped out the board for a BTT E3 RRF and installed their copy of marlin.  I suppose the "parking" at the end could be different now.  Is that somewhere in the firmware?  
> **username_0**: As far as the ballscrew question:   For the z drive it was just the stock ender 3 pro with the anti-backlash nut from that video I linked.  
> **username_1**: I think the parking is in firmware, but I can't picture why you'd park above the new part instead of clearing the hot end and gantry and then pushing the part out front.  

---

## 1 answers

### Answer by username_1 on 2021-06-03. Score: 1 | Accepted answer

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).

> **Comments:**
> **username_0**: Who knows if I should have officially "accepted" this answer until I try it all, but very helpful info so I went with it.  I'll check my firmware for both the "parking" and the resume feature (it didn't say anything like that on the screen, it just said 'ready', but again, maybe that was not in the firmware.  

---

