Source
r/prusa3d•
366df

Mini+ belt tensioner bolts and failing X-axis calibration

Hey,

I recently assembled the mini+ kit and the wizard ends in an X-axis error. I was going to disassemble the whole X-axis assembly but when I loosened the screws that hold the X-axis belt tensioner bolts that help keep the two rods in the plastic part and accidentally tested the X-axis again the test succeeded. Then I tried fastening the bolts again and the calibration started to fail until I loosened them.

So the screws on the left picture are open and the calibration succeeds and when they're fastened it fails.

Does someone have a clue if having the two screws loose is a problem or not? And if it is then how should I fix it and what's the cause? Even when the X-axis calibration failed, it seemed to work just fine, running the whole width of the axis three times without any problems.

pic

Edit: now that I look closer, the screws on the left picture actually block the nozzle assembly (one of the fans hits the screw) which stops the x-axis moving further. This is when the calibration succeeds. If the assembly is _not_ blocked by the screws then it will fail. So basically, the tensioning belts are too tight and the reason why they need to be that tight to have proper tension is somewhere else. The only reason I can think of is that the belt isn't far enough in the nozzle assembly grooves. Thoughts?

Posted Sep 6, 2021, 9:26 AM UTC · edited

110
veproza•

Those screws adjust belt tension. If after loosening the belt is still tight, roughly so that it makes a sound when prodded (as in a guitar string), then it was over-tightened previously. If it's loose, your prints will be somewhere between ugly and failing.

There was also an issue in earlier firmware with too sensitive failing of the test, so make sure you have the latest firmware installed.

Then first tighten the belt as per the manual and with the printer still off, move the carriage by hand, sensing if it moves smoothly and without resistance. Then try running the test. If it fails for x-axis, try first running the x-belt via the menu through the whole length (settings -> move axis). Then try the test again, some Minis, including mine, have an issue that it wouldn't run "cold", but it started passing after this warmup exercise.

1
366dfOP•

I thought the screws in the end adjusted belt tension and the one's on the side just clamped on the rods? Because the screws at the end seem to push the rods and therefore move the tensioner further away taking away the belt slack. The tension on the belt changes when I tighten the end screws but nothing really happens when I tighten the side screws. The belt tension seemed tight enough and doesn't seem like a factor because if I simply tighten the two side screws (left pic) the X-axis test will fail but if I loosen them it will succeed - belt tension seems unchanged.

I gotta check the firmware for sure though. The nozzle assembly slides on the X-axis without any problems either by hand or via the LCD.

1
veproza•

Damn, thought you were talking about the tensioning screws. Apparently I can't tell my left from right, sorry!

I think those side screws hold the axis-end assembly together, with them loose, the X axis might be wobbling in X and Y directions. I'd check the firmware and then, if the print head slides without resistance and can be controlled via the manual Settings -> Move Axis dialogue without issues, I would ignore the self-test and try a print.

IIRC my self-test X-axis was also failing intermittently unless I had the X assembly loose, but test prints came out OK. I have been printing for over a year since without issues and without self-testing :-)

1
366dfOP•

I upgraded the firmware, old version was from this february. I kinda forgot about tightening the screws and printed with them loose. Made an almost perfect looking benchy after finding a Z-axis offset (-0.700) that worked for me.

Edit: I actually noticed that when the X-axis calibration succeeds and my prints come out great, the nozzle assembly is actually blocked by the side screws in the tensioner. So basically something is off but two wrongs apparently make a right. I suppose the gantry has to come off after all and I'll have to check if the belt isn't far enough in the grooves. The way I see it only that and the tensioner can contribute to the belt tension?

1
boxcorsair•

Are the rods pushed fully into the end cap? There is a little observation slot if I remember correctly. Might be worth checking as certainly on my kit this was a very tight fit

1
366dfOP•

They were until I tightened the end screws for belt tension (their function seems to be to move the end cap away from the rods tensioning the belt)

1
mgc418•

The end screws are threaded into the plastic and tension the belt. The side screws squeeze the rods to help hold the end cap in place to help keep the threads of the end screws from stripping under pressure. The end screws are also used to help eliminate X-Z skew. Tighten the top and loosen the bottom brings the nozzle closer to the bed. You should for sure make sure the rods are seated all the way correctly. If they are not, you may be introducing a twist to the axis when tightening the side screws.

1
366dfOP•

I happened to print a very good looking Benchy with the screws loose so I'm a bit hesitant to change anything :D Those changes would probably affect the Z-axis offset if the nozzle moves closer to the bed with the lower tensioner screw looser than the upper?

1
mgc418•

You want both of the end screws to be tight against the rods

1
366dfOP•

Yeah I did that and stopped caring about failing the X-axis calibration, still printing fine. I will eventually have to pull the X-axis apart because the only other reason I can think of why it fails is because the tensioner screws need to be too tight and pull the tensioner outwards too much is because the belt isn't properly far enough in the grooves of the plastic piece that holds its both ends. I guess another option is that the rods near the Z-axis extrusion aren't as far back as they should.

1