X-axis just won't pass self-test (but seems to work fine?)
I got the MINI+ as a kit (because I built an i3 in the past and it was a great experience), and right after finishing the build, the self-test failed on the X-axis. I tried variously tightening or loosening the belt, which either made it fail on the very end of the first X axis sweep, or on the third, or on the second, etc. (It always was the very end though, when the head "slams" into either end of the axis). I couldn't see any skips with my eyes, and the travel was smooth across the entire X-axis.
Ultimately, I ended up accidentally "digging a hole" inside the X-end, because I loosened and tightened it so much the nut for the rod tightening screw got stuck on the screw, and ended up just rotating inside the printed piece, meaning it couldn't be tightened or loosened anymore.
So, I ended up printing another X-end on an i3 I thankfully managed to locate, this time on .15mm layer height, 4 perimeters and 40% infill (the most "robust" print settings I know of, save for just going 100% infill, so that the nut incident doesn't happen again), installed it... and it worked! The self-test passed, the (indispensable) Benchy looked as pretty as ever. I thought that was the end of it, so after a couple prints, I went to move my printer from my workbench to its designated spot, and just to make sure nothing had happened in the meantime, I ran a self-test, and... it failed on the X axis.
So I took the printer back, loosened the belt, tightened the belt, loosened the rods, tightened the rods, checked the grub screw on the X stepper (tight as ever), and it happened again - the nut got stuck and dug a hole inside of the X-end. So I grabbed my last spare X-end, looked on the net, ended up disassembling the entire X axis to really check for any mishaps, re-set and re-tightened the X motor, no avail. It always just fails with an X on either the first or second X-axis "slam".
The thing is, though, it seems to work just fine? I'm actually printing another X-end as we speak (just in case the X-end ends up giving in again as I fiddle around with it), and the print looks 100% okay - no layer shifts or weird x-axis noises.
I guess I could just leave it be, but I'm worried about what does the self-test fail imply (especially since it worked before), unfortunately the test results don't really say much. If I at least knew what it actually checks, I might be able to troubleshoot it better, but right now I'm just left tightening or loosening various screws, trying to appease the self-test procedure until the printed part fails.
Anybody have any ideas?
Best Answer by thm:
Figured it out!
It was the X axis rods not being fully seated in the Z-carriage.
I found out about the feature where the self-test writes a log to the USB drive (also solving the mystery "why does the self-test 'sometimes' crash to watchdog reset?"), saw the rather high length of 188mm, googled a bit, and found this prusaprinters forum post. Sure enough, albeit the rods seemed perfectly equal in length (as in, the part that protruded from the carriage), they were both a couple (2-3?) millimeters away from being fully pushed in, which took quite a bit of force. I suppose my fiddling with the X-end must've been enough to change the length of the axis so that the selftest sometimes measured just under the limit it considers OK, and sometimes just over it (assuming the check works this way?).
Anyway sorry for the post that I ended up solving myself, but still, thanks everyone! And especially Joan, I'm glad to have learned that anyway 🙂
PS: What was really weird though, is that just when I was about to disassemble the X axis for the n-th time, and all the screws were undone on the x-end, I ran the self-test and it suddenly tested OK. I have no idea why, but (before I fixed the z-carriage) it was only in this state that the selftest ran okay, as the printer head just magically stopped roughly about 1cm before it reached the very end of the X axis. There was no obstruction, and nothing different that I could feel by manually moving the printer head around that spot, and when I re-tightened the screws, the head went past that spot and slammed into the x-end as expected, and the selftest started failing again. That was also a clue there's something weird about the length of the x axis.
PPS: It would be great if there were more info regarding the selftest in the knowledge base; like the content Joan's post, or what do the numbers in the log on the USB drive mean? I can only read the "length=" portion with certainty, but I'm sure the rest of the lines might be helpful too.
RE: X-axis just won't pass self-test (but seems to work fine?)
Hi,
One picture could tell more than 100 words.
even an old man can learn new things 🙂
Standard I3 mk3s, MMU2S, Prusa Enclosure, Fusion 360, PrusaSlicer, Windows 10
PRUSA MINI+ Prusalink + Prusa Connect
RE:
Sure, but what would you like the picture of exactly? 🙂 The X-end? The cross on the screen indicating "fail"? The entire printer? The X motor? The prints?
RE: X-axis just won't pass self-test (but seems to work fine?)
Both the Mini, and the mk3 used stall guard to identify the ends of the axis, instead of limit switches,
If anything causes extra resistance to travel, during initialisation or collision recovery, the VIRTUAL limit switch (Caused by the stepper motor sensing a stall condition, can be set in the wrong position.
the printer 'Knows' that the X axis on a Mk3, is just over 250mm long, but if the x axis motion stalls at say 20mm, then the printer will think it has 250mm travel, from the 20mm position... and the printer is likely to collide with the right side of the Axis.
sometimes lack of lubrication causes problems, as do mis places Zip Ties, failing bearings, overtight bearing clamps foreign objects jamming movement, modifications such as fan grills, loose screws.
See if the X axis moves smoothly from end to end of the travel, by hand, when the printer is at rest.
If you feel jerkiness, or rough movement, investigate why that is happenning.
If you didn't lubricate the smooth rods and Linear Bearings during assembly, now might be a good time to do some periodic maintenance. and try lubricating the smooth rods with the grease, supplied with the printer.
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE: X-axis just won't pass self-test (but seems to work fine?)
To re-emphasize something Joan wrote in her reply, one thing the OP didn't mention was checking for correct placement of the zip ties or interference by one of the wire bundles. Been there...
Formerly known on this forum as @fuchsr -- until all hell broke loose with the forum software...
RE: X-axis just won't pass self-test (but seems to work fine?)
Figured it out!
It was the X axis rods not being fully seated in the Z-carriage.
I found out about the feature where the self-test writes a log to the USB drive (also solving the mystery "why does the self-test 'sometimes' crash to watchdog reset?"), saw the rather high length of 188mm, googled a bit, and found this prusaprinters forum post. Sure enough, albeit the rods seemed perfectly equal in length (as in, the part that protruded from the carriage), they were both a couple (2-3?) millimeters away from being fully pushed in, which took quite a bit of force. I suppose my fiddling with the X-end must've been enough to change the length of the axis so that the selftest sometimes measured just under the limit it considers OK, and sometimes just over it (assuming the check works this way?).
Anyway sorry for the post that I ended up solving myself, but still, thanks everyone! And especially Joan, I'm glad to have learned that anyway 🙂
PS: What was really weird though, is that just when I was about to disassemble the X axis for the n-th time, and all the screws were undone on the x-end, I ran the self-test and it suddenly tested OK. I have no idea why, but (before I fixed the z-carriage) it was only in this state that the selftest ran okay, as the printer head just magically stopped roughly about 1cm before it reached the very end of the X axis. There was no obstruction, and nothing different that I could feel by manually moving the printer head around that spot, and when I re-tightened the screws, the head went past that spot and slammed into the x-end as expected, and the selftest started failing again. That was also a clue there's something weird about the length of the x axis.
PPS: It would be great if there were more info regarding the selftest in the knowledge base; like the content Joan's post, or what do the numbers in the log on the USB drive mean? I can only read the "length=" portion with certainty, but I'm sure the rest of the lines might be helpful too.
RE: X-axis just won't pass self-test (but seems to work fine?)
it's possible that loose screws allowed something to 'bed in' or reduced a component of friction...
Don't worry about fixing your own issues in public, issues like this can sometimes encourage others to have a go, rather than expecting someone else, who can't see, touch, feel, hear the printer to magically respond with the correct answer...
thanks for contributing,
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK