MK4S Upgrade X & Y layer shifts by 20mm  

RE: MK4S Upgrade X & Y layer shifts by 20mm

FWIW, I am in the same boat - I just discovered this today. 

Two things to try: 

1) Ensure the printer is on a totally stable surface (this is NOT the case with mine, and I will need to adjust this in the morning)

2) Ensure the set screws are tightened on the x and y axis pullies. I suspect that mine have loosened due to 1) above (again, will try in the AM).

I am guessing that you pass x- and y- axis calibration, that the belt tension is correct, and there are no obstructions near the pullies. ( https://help.prusa3d.com/article/layer-shifting_2020)  

Good luck! 

RE: MK4S Upgrade X & Y layer shifts by 20mm

Are you using the speed profile?  Try raising the nozzle temperature.  I've found with the higher 4S speeds underextrusion is a problem.  Raising the nozzle temperature can help. 

Underextrusion can lead to crashes, causing the layer shift.  Especially in areas of big infill where the sides are higher. 

RE: MK4S Upgrade X & Y layer shifts by 20mm

I had this layer shifting problem on my factory-assembled MK4 when I started to use the IS profiles. After some time I checked and tightened all the screws on the printer and the problem went away. Check especially all the screws involved in the x and y axes, as @happykatz said. Screws on the printer tend to come loose(r) over time.

RE: MK4S Upgrade X & Y layer shifts by 20mm

Thanks for the feedback all!  I'll give the machine a once over to ensure everything is tight, especially the pulleys (never thought about that).  Yes it passes calibration but i'm going to give everything a once over today and try again.  It is on a stable base and still seems to be contained between the bumpers of the Prusa enclosure so i'm guessing loose pulley or layer crash as suggested above.

This was a structural profile, i don't tend to use the speed profiles. You have ALL given me some good insight into other potential source of issues, MUCH APPRECIATED! 

Will report back later after some maintenance!

RE:

Update on my end - pulley screws were reasonably tight, but the screws holding the motors and the extruder had loosened with the vibrating of the printer. After tightening these, I wanted to see if the problem persisted, especially if I could see evidence of underextrusion.

@brian-12, This appears to me to be what is happening: I am attaching pic below. Is this what you would expect to see ? 

RE: MK4S Upgrade X & Y layer shifts by 20mm

It looks to me like the infill printed very poorly, which is what prints the fastest. 

I'd try raising nozzle temperature 10C.  What filament are you using? 

The other thing I'd recommend is watching the print so you can see what's happening, especially when it starts the infill. If it starts to print poorly pause the print and take a picture. 

RE: MK4S Upgrade X & Y layer shifts by 20mm

Well I'm loading my first print again after some serious overhaul of the machine. 

I gotta say i'm pretty disappointed in myself.  I work as an owner's engineer and I know the value of a good PM program to the lasting life of an asset.  So of course i brought that knowledge to my personal life?  No. In the year i had this MK4 i don't think i re-tightened anything.  Ugh... well lesson learned, putting together a pre flight checklist and regular checklists for weekly, monthly and yearly.  The the worst part, I had a thermistor failure last week that required me to remove the heatbed, still didn't tighten anything when i had the printer disassembled, and a bit of foreshadowing but i'm pretty sure my haste in that repair is the root cause... 

So I did a complete once over of the machine this morning and can report:

1.  X & Y pulley's: both tight
2. Most screws on the X and Z were "loose-ish including motor mounts".  Everything on the Y was tight but I'm assuming that's only because of the MK4S upgrade completed a month back.
3. X belt - SLOPPY LOOSE just wow, very upset i have not even checked this.  This was my primary suspect of the X-shift i was seeing.  Assumption the loose belt was jumping gears. 
4. Y-Belt - a little tight so backed it off.  And have to say still not a fan of the belt tuning app.  
5. As i was loading the print back into the Enclosure I happened to notice a metallic spacer just lying in the base of the enclosure.  After a quick investigation, I found it to be the spacer for the center screw of the heatbed.  As mentioned above I had a heatbed thermistor issue last week which required the bed to be removed.  I'm assuming when i reinstalled the bed i clearly missed this spacer is free floating and it likely miss aligned.  While the bed tightened with the spacer likely sandwiched beside the center screw and would have only been temporary friction fit.  Alternative Root Cause (or supporting cause), this spacer likely eventually became miss lodged several prints later and jammed as it fell during a print causing the issues i originally reported. 

Sharing all the dumb things I did here as a reminder for others to do preventative maintenance and take your time and consult the manual and pictures during reassembly.

I've got the printer back in service and will keep an eye on things but i suspect that a combination of poor maintenance and that the issue should be resolved.  Will report back in a few days once i put a number of prints through it again.

RE: MK4S Upgrade X & Y layer shifts by 20mm

Filament is the "made for prusa" PETG turquoise blue - the filament itself seems to be going down solid, and I don't see evidence of shredded or underextruded infill.

The extrusion irregularities seem to show up in the first solid top layer, and then multiply after that, leading stray to filament accumulating on the nozzle, creating blobs, when then cause the layer shift when the nozzle runs into them.

Because this was accompanied by the occasional unload fault, I finally broke down and opened up the nextruder (see pic).

I cleaned this out, and am now printing the test part again: my working theory is that the filament shreds in the nextruder impeded the continuous forward advance of the filament at high speed (unlike with the infill, which proceeds at high speed, but experiences retraction on travel).

The thing I don't understand is why, if the crash is detected, does the print not pause ?

RE: MK4S Upgrade X & Y layer shifts by 20mm

If it's any consolation - you're not the only one in that boat, and the pre-flight checklist makes a lot of sense. From what I saw, I would also add regular inspection and cleaning of the Nextruder.

One additional note: in my case, while the looser connections made the layer shifting possible, the root cause was more insidious. My build plate is more prone to warping on one side than the other, and so my part was gradually lifting during print. When I got to the top layer, I had a gentle lift of around 0.5 - 1MM, which was enough to raise the left side of the part to the point that the nozzle was digging slightly into the layer, causing a blob, and then the crash, and then the shift. 

Why did the printer not pause when a crash was detected ?

From my last run, it looks like the digging triggered a stuck filament warning rather than a crash detection: I think it's triggering the wrong error, and so gives the wrong response. 

All that is to say - if it happens again, I'd double check that you're not getting any lifting off the build plate, and if you are check that the heat bed is maintaining a uniform temperature.

Now back to my regularly scheduled holiday 😉

RE: MK4S Upgrade X & Y layer shifts by 20mm

Crash detection does not currently work with input shaping.

RE: MK4S Upgrade X & Y layer shifts by 20mm

Ah HA!

I'm having the same problem-- layer shifts after a blob and no detection or recovery. I was thinking of proposing a feature request to enable stopping the print and re-homing before resuming. I never had a problem on my MK3, so I didn't know what crash detection did!

So does it work if you disable Input Shaping? Is that even an option? 

RISPONDI: MK4S Upgrade X & Y layer shifts by 20mm

Posted by: @johnnym

Ah HA!

I'm having the same problem-- layer shifts after a blob and no detection or recovery. I was thinking of proposing a feature request to enable stopping the print and re-homing before resuming. I never had a problem on my MK3, so I didn't know what crash detection did!

So does it work if you disable Input Shaping? Is that even an option? 

Yes, if you disable input shaping the crash detection can be enabled in the menu.  What it does if there's a crash is re-home the axis and the resume printing.  If it happens too many times it will pause the print. 

I will say that at least on the MK3 it was not perfect as there would usually be a visible line in your part where the crash happened and often a blob from oozing, however the print would usually be salvaged.  I think the best part was usually preventing the blob of death.