Print Problems - Please Advise  

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sara.s
(@sara-s)
Active Member

So, I've been doing pretty good troubleshooting my MK3S until now. Tightened up my X and Y belts, fixed a loose X-axis pulley, adjusted the tension on the idler... And I was getting almost-perfect prints.

Four times in a row I got otherwise perfect prints (though I stopped two early) with a single, tiny layer shift. X axis only, the Y is perfectly aligned.

The layer shifts never happened in the same place twice. So, I decided to do some pre-loaded test prints to rule out software issues, and well... Things Got Worse:

[caption id="attachment_3265" align="alignnone" width="300"] Nefertiti Fails[/caption]

(why are all these pictures sideways when they're upright in my gallery...)

Most spaghetti monster fails I've read about involve issues with first layer adhesion, but that's not my problem. It's looking to me like maybe a layer is getting skipped/under-extruded and then later the print is breaking off at that weak point?

I'm not sure how this connects to my layer-shifting problem, unless it's not under-extrusion but a layer shift that's causing the weak point, in which case... What is *up* with my X-axis? Why am I getting single points of failure in otherwise decent prints?

(I've been using the PLA bundled with my kit) 

...
Posted : 31/07/2019 5:30 pm
Tim
(@tim-m30)
Illustrious Member

When inserting images, use the LINK TO : MEDIA FILE option.

Two issues happening: 

One is very easy to fix, and you will thank me later:  Keep hands and fingers well away from the print surface. PLA and fingerprints are archenemies.  (This is not causing problems, yet, but will if you keep touching the print surface).

Two is you are having friction related layer shifting. You need to verify both axis move freely and with zero sticky points through the full range of motion. Power off the printer. Extruder must freely slide left/right to the stops.  Bed must slide front to back without any sticky spots.  I can lift and tilt my printer and the bed slides to the other end; same for the extruder. Though the extruder take a bit higher angle. 

Y-axis friction often comes from the U-bolts holding the bearings on are too tight. And X-axis friction from the extruder housing screws near the bearings being too tight.

Another issue is the bearings really do need to be packed with greased before they are installed on the rods.  But after the fact, spread some grease on the rods and work the grease into the bearings best you can.  This also helps friction.

To verify you are having friction issues, you can check the LCD status menus and look for crashes detected.  More than 0 is a sign something is too tight.

Another possibility is the X and Y belt drive gears aren't properly attached to the motors.  Very often the set screws are tightened out of order, which allows the gear to spin on the shaft.  Here's the proper assembly method:

Flat First: Drive gears must be tightened flat-first.

1)   Start with both set screws fully loosened so the pulley is free to spin on the motor shaft.

2)   Align one set screw dead center with the flat on the motor shaft, slowly tighten the screw until it fully contacts the flat surface.

3)   Torque the flat set screw to spec.

4)   Now tighten the jam set screw, and torque it to spec.

Once tightened, never touch the flat set screw unless the jam screw is first fully loosened.

Why Flat First? Set screws have flat ends. If you tighten the jam screw first the set screw on the shaft flat doesn't fully contact the shaft, only one small edge of the screw surface is biting. Reversing torques can easily shift the shaft to a position the flat screw no longer contacts the shaft. This lets the jam screw wriggle loose. And after a while, vibration loosens the screws until the gear is free to rotate.

 

This post was modified 1 year ago by Tim
It is always wise to get more than one opinion......
Posted : 31/07/2019 8:49 pm
sara.s
(@sara-s)
Active Member

(Is there no way to edit posts?)

Update: I think I've discovered part of the issue. I started printing Nefertiti again and this time I caught it in the middle of crash detection. It went back to home position, but when it resumed the new layer was that tiny bit out of alignment with the previous layer. I stopped the print and I'm currently printing another Nefertiti with collision detection turned off. So far so good.

So the new question is: why is crash detection triggering and how can I fix it? (It looked like there might have been a nub of filament sticking up, but I don't know if that came about before or after the crash was detected) And why is the print resuming at the wrong spot after the crash-homing thing.

...
Posted : 31/07/2019 8:52 pm
FDM 3D Printing
(@olddutchie)
Active Member

Hi Sara,

if you look into the LCD menu under "support" and scroll down to "belt tension", what values does it give for X and Y?

Posted : 31/07/2019 8:55 pm
sara.s
(@sara-s)
Active Member

Whoops! I was writing my update when you replied, Tim! There's a very solid answer for the crash detection. 🙂 I'll run through your suggestions ASAP. I didn't know that about greasing the bearings! That sounds like something that could do to be added to the manual.

I'm aware of the fingerprint issue, I just got lazy wiping the bed during my troubleshooting. Poor practice, I know, haha. I'll give the print bed a nice wipe with iso once everything is tweaked. 🙂

Thank you for your detailed run-down!

...
Posted : 31/07/2019 9:05 pm
Tim
(@tim-m30)
Illustrious Member
Posted by: FDM 3D Printing

Hi Sara, if you look into the LCD menu under "support" and scroll down to "belt tension", what values does it give for X and Y?

Again - the belt tension numbers are meaningless for belt tension. They report average friction the motors must overcome to move the axis, and are updated only after a self test is run. They are not indicative of sticky spots on the rods that cause crashes.

It is always wise to get more than one opinion......
Posted : 31/07/2019 10:31 pm
sara.s
(@sara-s)
Active Member

Update! The Y-axis slides just fine, but the X-axis definitely has friction issues. I completely readjusted the drive gear (I had already adjusted it once because it came loose from the motor shaft, but I figured I'd give it another adjustment sticking to Tim's guide). I've also loosened up the screws on the extruder casing. Time to self-test, calibrate, and try again! Depending on results I'll try loosening the casing further.

Thanks for the advice! 🙂

...
Posted : 31/07/2019 11:47 pm
sara.s
(@sara-s)
Active Member

Well, out of the frying pan and into the fire. Tried to test things out and I ended up with two clogs in a row. One that I managed to clear out by taking off the nozzle, and the second that's jammed so solid I'm pretty sure I have to replace the PTFE tubing. This is not my day for 3D printing! 

...
Posted : 01/08/2019 9:17 am
FDM 3D Printing
(@olddutchie)
Active Member
Posted by: Tim
Posted by: FDM 3D Printing

Hi Sara, if you look into the LCD menu under "support" and scroll down to "belt tension", what values does it give for X and Y?

Again - the belt tension numbers are meaningless for belt tension. They report average friction the motors must overcome to move the axis, and are updated only after a self test is run. They are not indicative of sticky spots on the rods that cause crashes.

Dear Tim,

I'm not even going to discuss with you since I've noticed that you know it all, but let me say this: I love how you start the sentence with "again".... I'm very happy to see that you take the time to teach us, your other forum members. It seems that we can all stop posting questions and issues here on the forum and just contact you directly, since you apperently have the solution for every occuring problem and other forum members are just plain stupid? Great! 

Posted : 01/08/2019 11:23 am
Tim
(@tim-m30)
Illustrious Member
Posted by: FDM 3D Printing
Posted by: Tim
Posted by: FDM 3D Printing

Hi Sara, if you look into the LCD menu under "support" and scroll down to "belt tension", what values does it give for X and Y?

Again - the belt tension numbers are meaningless for belt tension. They report average friction the motors must overcome to move the axis, and are updated only after a self test is run. They are not indicative of sticky spots on the rods that cause crashes.

Dear Tim,

I'm not even going to discuss with you since I've noticed that you know it all, but let me say this: I love how you start the sentence with "again".... I'm very happy to see that you take the time to teach us, your other forum members. It seems that we can all stop posting questions and issues here on the forum and just contact you directly, since you apperently have the solution for every occuring problem and other forum members are just plain stupid? Great! 

Okay - I'll bite. Why are you asking about the belt tension numbers?  Please, enlighten me.

It is always wise to get more than one opinion......
Posted : 01/08/2019 7:07 pm
bobstro
(@bobstro)
Illustrious Member

Might a self test be useful, if only to confirm it doesn't detect anything?

My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 01/08/2019 8:49 pm
danmackenzie174
(@danmackenzie174)
New Member

Tried to test things out and I ended up with two clogs in a row. One that I managed to clear out by taking off the nozzle, and the second that's jammed so solid I'm pretty sure I have to replace the PTFE tubing.

Firstbank card...
Posted : 05/08/2019 7:25 am
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