Several Problems emerging with my MK3S  

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Koyo
 Koyo
(@koyo)
Active Member

I've been experiencing strange oscillating noises mostly on my X-Axis for a couple of months, and now print issues on my MK3S

 

I've replaced the X-axis linear bearings several times. First from the original Prusa ones to replacement Prusa ones packed with Superlube 21030, and then recently to Misumi branded ones after packing them again with Superlube 21030.

 

The print is PETG at 240/90 and sliced with PrusaSlicer 2.3.0, however, this problem occurs regardless of what filament I'm using, or if the filament is even loaded.

 

[Video 1]

 

[Video 2]

 

[Video 3]

Image of print attached

I've tried adjusting how tight screws are on the back of the X-Axis, the Trapezoid nut screws, the belt tension (which strangely enough seems to change the position of where the Oscillation sounds the worst, tightening it moves it more to the right side, while loosening makes the left side worse), and almost anything else I could think of, but to no avail. The one thing I tried that almost eliminated the sound, was completely unscrewing the X-Axis stepper motor and holding it in place by hand, although that's not practical for printer use. Perhaps investing in a stepper motor dampener would help?

As for the print quality issues, I'm at a loss. At face value it seems like Z banding, but this is the first print I've had with this issue so far. 

Any and all suggestions are greatly appreciated! Thank you

Posted : 18/04/2021 6:28 am
blauzahn
(@blauzahn)
Trusted Member

Have you measured the distance between the rods on the left and on the right side near the z-axis carriages with a caliper gauge?  With linear (roller) bearings a misalignment can go unnoticed for some time due to the relatively low friction coefficient of rolling contact within the bearings. And in case of the thin 8mm rods which bend a lot in the middle, for prints in the middle of the bed it can work for a while. With misalignment the load on the bearings can get very high. That leads to premature failure and, if high enough, instant destruction of bearing or/and rod. If the bearings were of friction-type, a misalignment might have blocked your axis right away.

 

Is the surface on the left z-carriage where the x-stepper is attached even? If not, the relatively stiff motor might bend you z-carriage. I doubt that this is the reason for your problem though. Just because you mentioned, that it appears to work when you unscrew that motor.

 

I assume your x-rods are intact. That is, they do have neither grooves nor are they bent. Are both of your z-rods parallel and not bent as well?

 

Did you check the tiny bearing of the beld idler on the right z-axis carriage?

 

MK3S MMU2, PEI + Powder Coated Sheets, Prusa Slicer, Arch Linux...
Posted : 18/04/2021 7:38 am
Koyo
 Koyo
(@koyo)
Active Member

@blauzah

Thank you for the great suggestions! I think you're on to something with the X rods alignment. The spacing on the left side is 36.7mm, while on the right side is 38.1mm. The rods themselves also vary in diameter by about .10-.15mm. 

I'll check the other points you mentioned in a bit, and update with the results. 

Posted : 18/04/2021 5:11 pm
Koyo
 Koyo
(@koyo)
Active Member

Actually, a correction on the rod spacing. It's actually not that bad, about 36.7 on the left and 36.9 on the right. 

Posted : 18/04/2021 5:20 pm
blauzahn
(@blauzahn)
Trusted Member

Are you sure about the rod diameter variance on your rods? That difference would be huge.

I just measured my upper x-rod (near top to bottom) with a good micrometer: right side: 7.990; middle: 7.991 left side: 7.992mm. The micrometer has a Tolerance of +/-0.002mm. I think the rods are supposed to have the quite common 8h6 tolerance. That means a minimum diameter of 7.991mm and maximum 8.0mm. So my rod is on the lower end of the tolerance field.

Distance between rods: I measured on the outside with my caliper (new Mitutoyo) since I feel it is easier to measure correctly. right side: 52.96mm,left side: around 52.92mm, I do not pretend for those to be more accurate than +/-0.03mm each.

 

MK3S MMU2, PEI + Powder Coated Sheets, Prusa Slicer, Arch Linux...
Posted : 18/04/2021 6:58 pm
Koyo
 Koyo
(@koyo)
Active Member

@blauzahn

Thank you so much for sharing your measurements so I can compare and figure this out. I'm only using a relatively cheap pair of plastic calipers, but using a similar method to yours, I measure:

Top rod

7.88mm on the left, 7.92mm on the left-middle, 7.95mm in the middle, 7.93mm in the middle-right, and 7.90mm on the right. 

Bottom rod

7.90mm on the left, 7.89mm on the left-middle, 7.91mm in the middle, 7.90mm in the middle-right, 7.91mm on the right. 

The top rod was actually replaced a couple of months ago, so with the significantly worse tolerance on the top rod, perhaps the replacement rod could be causing some issues. And to somewhat confirm this, when I run my calipers up and down the original rod (which I replaced due to scratches) the measurement is quite consistent at around 7.89mm, but with the replacement rod it's anything but consistent. I even struggle to run it back and forth smoothly, and the measurements vary greatly from 7.85mm-7.95mm.

Also in regard to the points you mentioned in your initial reply, the Z rods are straight, The left printed part of the X Axis end is flat where it meets the stepper motor, and as far as I know the X belt idler is fine. The belt does move side to side a bit on both X and Y, but from what I've heard that's pretty common and doesn't introduce any print quality issues. 

 

This post was modified 4 weeks ago 2 times by Koyo
Posted : 18/04/2021 8:38 pm
Clarmrrsn
(@clarmrrsn)
Honorable Member

In addition to the above suggestions when replacing the bearings did you ensure they were installed with 2 rows of ball races evenly distributed over the top of the rod, this can cause extra noise/vibration if only 1 on top?

How are you checking belt tension?  The electronic test is not accurate.

Print this in petg and check tension https://www.prusaprinters.org/prints/46639-tension-meter-for-the-gt2-belts-of-i3-mk3s-or-prus

Check the motor pulley has clearance between it and the motor, and that the belt is not rubbing in the gaps in the end caps.  Check the idler pulley screw is not too tight, also check for dirt on the teeth of  both pulleys, this can cause vibration.

Tank you very much!...
Posted : 18/04/2021 10:41 pm
Swiss_Cheese
(@swiss_cheese)
Honorable Member

I watched the videos and I listened closely to the sound, your printer sounds fine to me in the "Prusa loud solid infill" video, in the X axis video it sounds like un-lubed LM8UU bearings rattling it's also possible that the screws that holds them are to tight causing them to bind, but I really can't diagnose that one from your video, so that's just my best guess based on the information at hand.

 

Now, the print that your showing of the watering pot, that is a completely unrelated issue. The bands on the watering pot are caused by a lack of adjustment (tuning) on your part, the walls are thin and you need to adjust the extrusion width in order for them to print properly, as it happens I know this because I printed that exact same pot several years ago, and made the exact same mistake and mine looks exactly like yours before I figured this out.

 

Notice any similarities?

Note: this was printed with Hatchbox White PLA hands down the worst white PLA experience I have had to date, I was printing this to try and get rid of the last of it.

 

once you learn about setting extrusion widths and layer heights as well as sometimes using different size nozzles you will start to see these problems go away, BTW the big band in the middle is caused by something completely different from the extrusion width issue.

Thingiverse, Myminifactory, prusaprints and alike are model repositories, there is no guarantee that the models are properly constructed nor where they necessarily designed for FDM/FFF printing even if they were properly constructed, and I fear you may be on a wild goose chase thinking something is wrong with your printer.

 

These are my opinions based on the info you provided and my experience.

 

Good Luck,

 

Swiss_Cheese

Posted : 19/04/2021 2:44 am
Koyo liked
Koyo
 Koyo
(@koyo)
Active Member

@swiss_cheese

Thank you so so much for confirming that it's not a printer issue with how the self-watering pot came out. That narrows down the problem a lot for me, as I would have for sure as you mentioned, went looking for a while to try to solve that issue. 

Posted : 19/04/2021 2:50 am
Koyo
 Koyo
(@koyo)
Active Member

Update:

I got a replacement rod, and just swapped it out. It's not completely perfect, but it's quite a lot better. The super loud parts seem to be a lot more reasonable. It also does not seem to be an uncommon issue so I think this is about the best I can get it. 

Before Video

After Video

Thank you to everyone for the suggestions! 🙂

Posted : 20/04/2021 11:07 pm
Swiss_Cheese
(@swiss_cheese)
Honorable Member

I'm glad to hear that, now you can move forward and start having some fun.

 

Enjoy

 

Swiss_cheese

Posted : 21/04/2021 1:42 am
Clarmrrsn
(@clarmrrsn)
Honorable Member

Good news indeed.

There are always a few teething issues in such a complicated build.

😁👍

Tank you very much!...
Posted : 21/04/2021 9:41 am
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