Z axis trouble but only when printing
New Prusa Core One. Replaced stock nozzle with Nextruder Diamondback Passed all initial checkouts and calibrations.
Was able to print a few parts and the quality was quite good.
Then gradually Z axis homing and nozzle cleaning became more and more challenging. With problems significantly more frequent when homing before print. The printer still passes all axis and load cell tests. Most of the time it homes successfully when commanded from the main menu. However when I try to start a print, the printer either moves the table up and down without touching the nozzle most of the time (sometimes moving the table progressively lower) or even if it eventually homes after several retries, claims to fail the nozzle cleaning (even thought the nozzle has been manually wiped clean).
In the lower 15% of Z axis during movement there is loud scraping sound. Most likely it is heatbed cable but hard to confirm since it's hard to get reach there when the bed is low.
Also when bed probing is done ~20% of points are probed multiple times with small X/Y shift between attempts. I don't recall seeing this behavior on MK4 or XL. Older models seem to occasionally double tap a point but without X/Y shift.
Spent a lot of time with Prusa support:
- Adjusted X/Y belt tension that was uneven. This reduced X/Y banging during homing, but didn't do anything for the Z axis predictably.
- Checked for Y axis gaps - there were none.
- Tightened the lead screw and Z stepper bolts a bit, though they seemed to be OK.
Later, without talking to support, lubricated all 3 z-rods. Didn't help.
At this point support is consulting the product team.
As I was typing this post, the printer finally homed after many retries and is printing just fine.
Seems that something is wrong with either the load cell or Z-axis. What else can I check?
A few other wild theories on what could have made the problem worse:
- I enabled the Stealth mode (firmware issue?). After the print is done I'll try to disable it and see if failure rate changes.
- I installed anti-vibration pads. Initially I was printing without them. But less vibration is usually good, right?
- One of the early prints ended up in spaghetti. It could be that filament fragment made it's way into the print head and is messing with the load cell (perhaps only when the head is hot?). Possibly a fragment is somehow jamming one of the lead screws, but it is unclear why it would behave differently when homing from menu or when running a print. Also I don't see any visible debris there and the filament in question is red, so should be very visible.
What else can I try as I'm waiting for a response from support?
It seems that majority of the users are not having this sort of problem with Z-homing or any problems at all.
RE: Z axis trouble but only when printing
You mentioned lubricating "all 3 Z rods". There are two rods and three lead screws for the Z axis -- which ones did you lubricate? From other posts discussing Z axis problems, I understand that it's the lead screws which needed lubrication in some printers.
RE: Z axis trouble but only when printing
Apologies. I meant 3 lead screws.
Prusa support advised following inspection of Z axis:
- Trap Nuts – Slightly loosen and then securely re-tighten them to ensure they aren’t causing unnecessary friction.
- Motor Stability – Tilt the printer to the side and inspect the motors from the bottom to see if any have come loose.
- Z Rod Holder – Check the back Z rod holder for any damage, as this can sometimes occur during shipping.
- Rear Trap Nut Securing Part – The rear trap nut has a plastic piece that secures it from below. Make sure it is properly in place.
Tried all this but didn't find any defects.
However I was able to narrow down the problem further.
Previously I noticed that homing works fine from the menu, but fails or severely struggles during a print.
I tried pre-heating the printer to PLA and doing homing from menu. I observed same failures as when during the print. Printer fails to home and reboots to red screen with message: "Failed to home the extruder in Z-axis, make sure the loadcell is working"
I cooled down the printer and heated only the bed. Homing worked reliably.
I started gradually heating the nozzle.
Fan turned on at 50°C but homing still worked. So extruder fan is unlikely to be the cause.
I kept gradually increasing the temperature by 10°C and somewhere between 100°C and 120°C I start seeing homing failures. After 120°C failure are pretty consistent.
So it has to be related with some interplay in the print head between nozzle heater and load cell.
Anyone seeing this sort of issue?
RE: Z axis trouble but only when printing
Any closure on this issue?? I just replaced my nozzle with the diamondback today and am having issues on my prints. It calibrated great, ran one 20min print just fine and now the extruder is skipping halfway into prints then the pla stops sticking. I played with temps and jothing is helping. Same exact speeds as when it was the brass nozzle.
RE: Z axis trouble but only when printing
The default brass nozzle is high flow. The diamondback is not (AFAIK nobody mades diamondback HF nozzles for Nextruder yet). So it's unlikely that you can use exact same speeds as with brass nozzle. You have to use non HF print profiles in Prusa Slicer and setup on HF nozzle configuration in the printer itself. Otherwise you can experience those extrusion issues.
RE:
Oh my god, I got the EXACT same issue;
https://photos.app.goo.gl/iK1WEauMJa55tWwr7
I did quite a bit of research, and found that it only happens when the nozzle heater is turned on
I raised a GitHub issue here; maybe we can centralise feedback to allow Devs to better solve the issue?
https://github.com/prusa3d/Prusa-Firmware-Buddy/issues/4596
I don't think it is the fan, since that does nothing special electronics wise.
I currently suspect that it might be;
- The load cell detecting strain when the heatsink heats up, due to expansion oft he metal
- Electronic noise\ interference I side the Loveboard of the PWM switched heater
I also saw this issue has been present on MK4/ MK4S
RE: Z axis trouble but only when printing
Hello @voxel3d_nederland,
The load cell detecting strain when the heatsink heats up, due to expansion oft he metal
Your issue seems to be harsh, but can totally be due to the cable bundle constrain over the loadcell.
If it is easily reproducible, could you try again after unscrewing the pneufit and releasing the two screws (not necessarily removing them) at the back of the nextruder?
In my case #4555 it helped a lot to solve this issue before the firmware upgrade. Maybe there is some threshold that have been adjusted with the last release that is not enough in your case.
(I'll post the related link to your github issue to link the clues)
RE: Z axis trouble but only when printing
I actually did loads more testing over at the GitHub issue I raised.
Took apart almost my entire machine and also tried removing the filament, as well as the entire Loveboard so nothing sits on the top of the load cell.
For me the issue for sure is electric noise inside of the ground that the ADC for the load cell is using. It connects the stable ground for analog with the normal ground when the Heater switches PWM on when the temperature is reached. This causes voltage spikes, which result in false readings.
Now, Ill need to search for a solution, maybe something else causes the noise in the ground. For sure I am curious of the design choice to connect a filtered gnd with a PWM heater-switched gnd.
RE: Z axis trouble but only when printing
Then gradually Z axis homing and nozzle cleaning became more and more challenging.
I'm also having the same problem. You've described very well what I've noticed after various tests. When the nozzle is heated, the problems get worse. I can no longer start any printing; it's become critical.
RE: Z axis trouble but only when printing
Same problem for me on 6.3.2 firmware. Nozzle cleaning fails with textured sheet and prusament petg. The bed won't touch the nozzle and just hover and attempt to tap. I've got 8 prints complete in total using asa / pla and have never used petg until I tried today.
RE: Z axis trouble but only when printing
Yesterday, I completely disassembled and reassembled the print head, carefully following the instructions. And the problem went away. After that, I managed to run several PETG prints. The automatic leveling and nozzle cleaning were successful quickly.
But today, when I started a PLA print, I still had a lot of trouble getting past the nozzle cleaning step. The problem seems to be gradually returning.
There are a few things I'm having trouble understanding. Where could this be coming from?