RE: Y-axis self test failing consistently
My fix was a zip tie on the Y smooth bar. Incredible that one has to Appalachian engineer a brand new machine to make it work.
RE: Y-axis self test failing consistently
Yah. My patience with anything involving 3d printing ended in November after about 2 months of watching this piece of shit bash its x carriage into its frame. I dont understand how the reviews of this company are so good. They have wasted so much of my time fixing parts that werent broken to begin with and never actually telling me a single thing that made the damn thing work. They just ask for more money. So im sorry for being prickly and just generally unhappy. This company really has pretty much ruined several months of my life at this pont.
RE: Y-axis self test failing consistently
Had this issue as well. Adjusting the bearings fixed it for me. Thanks to everyone here that suggested that.
RE: Y-axis self test failing consistently
just in case it may help someone in the community: my printer failed the Y test after a few months of faultless work. I discovered that pretty much ALL bolts were not tight anymore (and they were when I finished the assembly!). I re-tightened all the possible bolts, used the app to tune the belts (the Y belt was waaaay under the right tension and the X one was only slightly under tensioned) and the full test suite passed.
I was really surprised by how much the various bolts and belts got loosened after a few months of work; this said, the mk4 shakes a lot more than my old mk3s.
RE: Y-axis self test failing consistently
Exactly so. The Y-axis bearing spacing is finicky, so you have to be patient and willing to re-test, re-test, re-test. I used the same method as you, tipping the printer and moving the heatbed assembly fully to the rear to access the bearing clip screws. I also found it very helpful to have illuminated magnifying goggles to get sufficient visibility of the bearing recesses in the frame, as I think locating the bearings in reference to the recesses was key.
RE:
FYI finally fixed mine after many hours. For me I had to shift both bearings towards the front. With the machine on the side I slide bed to the back and make sure the rear bearing doesn't hit, the y belt holder hits, then for the front direction I put the bearing mostly to the front so the front bearing hits to stop the travel in the forward direction. I had to put the bearing pretty far forward. The manual has you move both bearings towards the center. I had to move both bearings towards the front, pretty far forward. It is working for now and has passed the calibration so we will see how it prints.What's somewhat ridiculous is that it failed the first few hours I tried, I rolled back to firmware 5.1.0 and it passed calibration. It has been printing for a few weeks. I wanted the new firmware and when I flashed to 5.1.3 the calibration failed again. Perhaps my bearings had shifted but the other best thing to try is roll back firmware. 5.1.2 failed for me as well initially. Now shifting both bearing to front I passed on 5.1.3.
RE: Y-axis self test failing consistently
Not sure if this is valid for everyone, but here is the analysis for my y-axis check fail and an easy solution:
So first of all, step 19 of the y-axis installation clearly states "position the bearings as close to the center of the Y-carriage as possible".
The bearings have a length of 24mm, the pockets width is 26mm, so there is ~2mm space to play with.
Analysing the construction, it was clear, that the alignment of the rear bearing is irrelevant, as the table's rear stop position is defined by the motor and the belt-holder, long before that bearing could touch anything else.
However, the front stop position is defined by the front bearing! So I was able to pass the y-axis-check by limiting the y-axis travel to the front by wrapping a wire of ~1.5mm thickness around the rod. This made the test pass!
But this was no valid solution for me, so the real solution was obvious: move the front bearing 1.5mm further away from the center and closer to the front.
This is clearly the opposite of what the building instruction says and it's unclear why such an obvious error exists.
I assume either a change in the firmware was not aligned with the instructions or the other way around.
At least it seems unnecessary to make the check fail because of ~1.5mm extra travel...
RE: Y-axis self test failing consistently
Hi
I had the same issue and found this site with Google. Just in case others get here also in this way:
I have the diy kit MK4 and passed every Test on the first try, but on the old firmware 5.0.
After three days I moved the whole thing (untouched in the enclosure) to a new room and installed the new firmware.
And from here I don't know what caused the problem.
Whatever, I found all those solutions who seems to work for some people:
- Bearings not lubricated enough, but re-lubricate seems to can solve the problem
-Check if all screws are where and how they should be
- dirt, dusk, filament waste on the rails/bearings
- tension too tight, too little
- (front) bearings postion centered too tightly (see previous posts)
What worked for me, and it's nearly a joke:
The foam rubber sticker from my 6 year old one...
I was to lazy to print a ring, as mentioned in a previous post, so I took the foam, cut a hole and placed it in the left front and passed the test...
It's clearly not a permanent solution, but the quckiest way to give a try. (on the Firmware 5.1.3)
Hope that helps 🙃
RE: Y-axis self test failing consistently
Hi,
So I have just finished the 3.9 upgrade and have the dreaded Y axis self-test failing 🤬
I started with the latest 5.1.3 firmware, but dropped back to the 5.0 - still fails
My bed never moves to the front. It goes to the back, bangs for a while, then it reboots and shows:
Do not understand how it can fail when it has not moved to the front!!
I have checked belt tension, pulley, there is nothing blocking the bed, I am at a loss
RE: Y-axis self test failing consistently
well, yes I am also hitting the wall here with this hardware/Firmware issue. With latest firmaware it doesnt pass the test, and I am left using the old Formware 5.0.0, then nothing to adjust but youre left with old firmware. Seems like Prusa doesnt care anymore for this isses which is shame. The thing is this machine is not really ready for the market and we're still like early adopters, shame shame shame.
RE: Y-axis self test failing consistently
i have a factory assembled mk4 and had y axis calibration failures. i tried fw downgrade to 5.00, but then the x axis failed and the y passed. i then found most if not all of the 2.5mm screws where not tight from the factory. i used the prusa tune app to check the belts and they were both loose. after tightening the screws and belts it calibrated with no issues on fw 5.1.3...
RE: Y-axis self test failing consistently
I am so glad I found this thread! For almost a year, I have been contacting Prusa tech support because my MK4 regularly detected a collision before prints. They had me run through the typical stuff - firmware upgrade, then firmware downgrade, etc.
Amazing how loose all the bearing mounts were under the bed! And yes, moving the front bearing back just a tiny bit fixed the problem and it now passes the Y-Axis test.
I think Prusa Tech needs to make note of this and suggest this before putting people through the useless steps of firmware downgrade.
Thanks, all!!!!!!
just in case it may help someone in the community: my printer failed the Y test after a few months of faultless work. I discovered that pretty much ALL bolts were not tight anymore (and they were when I finished the assembly!). I re-tightened all the possible bolts, used the app to tune the belts (the Y belt was waaaay under the right tension and the X one was only slightly under tensioned) and the full test suite passed.
I was really surprised by how much the various bolts and belts got loosened after a few months of work; this said, the mk4 shakes a lot more than my old mk3s.
RE: Y-axis self test failing consistently
Brilliant, been working on this problem for a few hours and this 211 mm reading really helped me out. Couldn't figure out what the cause of this Y-axis problem was and already dismantled most of the printer . Concentrating on creating more space while the opposite was required. My reading was also 211; moved the bearing out and problem fixed. Thanks a lot!
RE: Y-axis self test failing consistently
This is really clever. Would you please be so kind as to share the STL or model file?
RE: Y-axis self test failing consistently
We assembled with no problems at all. The same Y asis test failed. Moving bearings in all possible directions did not give result. our splution was zip tie on left rod, but for how long? 
RE:
Congratulations!I bought a mk4-kit - 2 pcs. One failed the y-axis test (the screen showed 211mm, which seems too much). It turned out to be a problem in the location of the bearings on the left. Although I did as in the photo in the instructions - the bearings are as close as possible to the center, but so that they do not touch the edge of the platform - that is, everything was the same on 2 printers. I moved one bearing (which is closer to the front side) by 1 mm from the center, that is, closer to the screen - this was enough to reduce the movement of the platform and the test was passed. Good luck!
This solved it for me: front left bearing, moving it a bit further away from the center of the plate (feels "against" the build instructions...)
It's actually counter-intuitive, since the build instructions (in particular step 20 of chapter 7, "Positioning of the bearings") makes it clear the bearing must be shifted as much as possible to the center of the plate, up to the point of just not touching the side. Well, I redid that part multiple times, but it's actually moving it further away from the side, so more in the center of the mounting mechanism, that it finally worked...
(note that the printer did pass the self-test when I built it, now about one week of almost-continual printing it started failing. I guess somehow the front left bearing moved a bit to the back, and then the self-test sees that the plate is able to move too far - see @miroslav-h4 's thoughts about the firmware checking that it moves too far?)
RE:
I ended up having the same problem. At first I tried moving the (left) Y-axis bearings closer and closer to the center of the bed. I tried re-tensioning the belt, double-checked the alignment of the bed, re-lubricated the bearings... and then I went into the "move axis" menu, moved the Y-axis all the way back to -4mm, and from there moved it as far forward as it would go. It stopped at +211mm, but there was a small gap between the bearing and the smooth rod holder. I went ahead and moved the bearing about 3mm forward, and that fixed the problem. I ended up with my front left bearing much closer to centered in its holder than the drawings would suggest (Maybe it's because I've got an old print bed with the cutouts/holes?)
Needless to say this was EXTREMELY frustrating. IMO, as long as the bed can move freely between -4mm and +211mm of Y-axis travel should be sufficient to pass this test. This took me about 6 hours of frustrated tinkering over 3 evenings to figure out.
RE:
I built my MK4 kit in Sept 2023. I think because my self-test was on FW 5.0, I never ran into this. Yesterday I upgraded to the FW 6.0.0 RC1 for MMU3 and now I can't get Z or Y-axis homing to work. I can confirm that the Y-axis hits 211 and just fails. I downgraded from 6.0.0RC1 to 5.1.3, 5.1.2, 5.1.0, 5.0.1 (and it passed the Y-axis test on 5.0.1.)
From what I read here, I guess I have to take apart the bed and try to tweak the Y-axis bearings even though this printer has been flawless for over 6 months.
Z-Axis homing totally fails as well. It claims the loadcell isn't working, but the loadcell test passes every time. This is with the PTFE tube from the MMU3 removed to reduce any potential drag on the nextruder. I have no idea what would cause this.
X marks the spot.
RE: Y-axis self test failing consistently
I designed and printed a 2mm clip and added onto the left Y-axis rod. Worked just fine. Thank you.
X marks the spot.
RE: Y-axis self test failing consistently
I see that there are still a lot of people who have this problem and @PRUSA has still not reacted !
I feel like user feedback no longer has any value in this company and that's a shame.