RE:
@nico-5
Hey, I feel dumb for not reading this earlier.
I just found out a similar...thing. My printer only exhibits this 'false probing' behaviour when the hotend is hot.
The severity is correlated to the temperature of the hotend:
- at room temp, the issue is not present.
- around 100C the issue is present, but infrequent.
- around 135C the issue is present, and barely manages to probe and clean the nozzle about half the time.
- at max temp, 280C -- the issue is constant, and the z-axis actually migrates up, as the retraction is greater than the distance it can move down between 'false probes'.
RE:
Procedure: I homed the printer while cool and moved the z-axis up to 200mm before heating to temp and starting the homing procedure. I only adjusted the nozzle temp for these tests.
These tests are with no filament loaded.
Room Temp: https://photos.app.goo.gl/ZBjCUD8aYRvfnN228
75C: https://photos.app.goo.gl/4FdjBWrW4DkRpZR59
125C: https://photos.app.goo.gl/1isbJsqDedfX9VEg7
175C: https://photos.app.goo.gl/1evHWwhsCQYiG1946
290C: https://photos.app.goo.gl/Un3KwmYzHKr4pELs5
RE: MK4 Probing for plate in mid-air | Issue homing Z-Axis when starting a print
This solved the problem for me. Again, the screws weren't loose, but tightening them up half a turn did the trick. No more mid air probe points! Thanks!
RE: MK4 Probing for plate in mid-air | Issue homing Z-Axis when starting a print
Hello,
I'm wondering if I'm having a similar issue. Here is what I'm seeing on my mk4.
Occasionally, the printer seems to get confused about the position of the Z axis. This seems to happen especially on taller prints. When this happens, the printer will start probing for the plate very high up. Even if I press and hold the knob, then turn the knob to move the Z axis. It won't move down past the point where it thinks the lowest point is, which could be half the way up the axis. Turning the printer off and on doesn't help.
The only way I've found to fix this when it happens is to turn the printer off and manually push the axis down to the bottom. Using the homing feature doesn't work when the printer gets in this state.
Does this sound like the same issue?
RE: MK4 Probing for plate in mid-air | Issue homing Z-Axis when starting a print
It sounds similar, yeah. It seems like it might be a little different.
After the printer homes the Z incorrectly, the knob won't send the printer past where it thanks the build plate it.
But my issue doesn't happen in one spot on the z-axis. It seems to have an equal change of happening anywhere on the Z. It seems most affected by the hot end target temperature.
RE: MK4 Probing for plate in mid-air | Issue homing Z-Axis when starting a print
All my screws were a bit loose. This time I used a ball allen with a handle on it instead of the tiny wrench included. I think between that and just "settling" from when it was assembled, a general overall tightening is in order.
RE: MK4 Probing for plate in mid-air | Issue homing Z-Axis when starting a print
Mine does this only when a USB drive is plugged in. It doesn't matter what USB drive or if it's printing from the drive.
It first started when the drive was slightly unplugged at an angle, and plugging it in fully fixed it. But now it's just whenever a drive is plugged in.
And it's precisely that the drive is plugged in during Z-axis homing. I can start a print over serial without it in, and if I plug it in before the Z-axis homes, it does this.
I can start a print over serial with it plugged in, and so long as I unplug the drive before it reaches Z homing, this problem doesn't happen.
I can even start a print from the USB drive, then unplug it before the Z axis homing starts, and it will do the whole print successfully.
I tried plugging USB cables into the port, and that doesn't cause the problem. It has to be a USB drive.
I also took the display board out, and didn't see any obvious damage. I posted pictures in an electronics group I'm in, and they didn't see damage either.
I'm really confused as to how this can even happen.
RE: MK4 Probing for plate in mid-air | Issue homing Z-Axis when starting a print
Just found this thread as I was having the exact same issue with my MK4S, and tightening the back plate screws worked for me. I had to turn them a varying amount for each, but almost all of them were at least 1 full turn.
RE:
This is an issue every single time I use FLEX. What the heck is it doing looking for the bed in mid-air? Power off, manually lower the head to about 1/4" off the bed and it occasionally finds the bed and usually calibrates. I turned it off and on several times and it skipped the calibration all together and started printing correctly. Wow. Apparently this has been an issue for years. What year do you think they will fix it? This failure rate is unacceptable.
RE: MK4 Probing for plate in mid-air | Issue homing Z-Axis when starting a print
Hey all, sorry it looks like I forgot to update this thread.
After six or seven months of troubleshooting with Prusa Support we eventually nailed down it was crosstalk between the power wires and signal wires for the bed probe. Specifically the joint where they are pinched together as they tie into the Nextruder. The assembly manual was updated to load the power and signal wires in separately.
There are many things that could resemble my issue, but what set mine apart specifically was it ONLY happened when the hot end was hot, and it got progressively worse as the target temp was raised.
So anything that is only affected by spool placement, or material choice, or anything other than hot end state/target temp is likely a different issue.
I would think about what is different when you use FLEX, specifically. Filament specific makes me think about tension on the filament during the homing cycle. Is your spool mounted differently? Does it spin or roll as freely? Sometimes my FLEX filament will stick to the lower layers a bit as it unspools. If you pull out some slack before the homing procedure does it still mis-probe? If you load in 6 inches of FLEX does it still do it as it homes?