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Update below

Printed 650 of these tokens, no problem. Then all of a sudden I can't get them to stick and the first layer looks wavy and weird.

Closeup

After a few tokens it knocks one loose and the whole print fails.

Did try to recalibrate the z-height. Should it be even closer? The test pattern for first layer height looks good.

Removed the nozzle to inspect if it's damaged but it looks fine to me...

Whole bed

Any help is much appreciated.

Update - Dec 29th 2019

With the new nozzle and recalibration I managed to get one more print to stick as in my answer below. Then back to not sticking.

I did order a textured plate from Prusa. Recalibrated the XYZ. That did not help.
I have played around with the first layer calibration. In the video below the setting of -0.900 is fixed the whole time. The lines look good and healthy but then lifts on the right side of the bed.
Video of first layer calibration

I then moved the nozzle even closer and REALLY smash it into the bed @ -1.050
It still lifts on the right side and a little bit in the corners. The first purge plastic that is output to the bottom left usually does not stick at all.
Untouched with nozzle closer

Things I have done:

  • Recalibrated the XY & Z axis from scratch.
  • Did two cold pulls of the filament (link) to make sure the extruder is not clogged. The pulled filament looked nice and clean.
  • Switched to new textured bed sheet
  • Switched to a new 0.4mm nozzle (E3D V6)
  • Tried different filaments (only PLA though)
  • Lubricated moving parts
  • Checked heat bed to make sure screws are tight and the bed sits snuggly

Two ideas now:
Can it be the mesh leveling that is acting up? How do I check that?
The heat bed feels differently warm in different places. Is the heat bed constructed with different zones where one can fail and the rest keep working? Do not have access to a heat camera to check.

Any suggestions would be much appreciated!

EDIT:

Thanks @Paulster2! It's good to find this community!
I've been using several different PLA filaments since this started happening. Before, they all stuck to the printing bed like champions, now none of them do. Pictured is som generic white, but getting the same result with Prusament PLA. Nozzle 215°C, Bed 60°C. As I wrote above, I did check the nozzle and it LOOKS fine. It's very small though and I have ordered new nozzles. If no one has any other suggestions I will post more when I have tried the new nozzle.
Also thanks to @Greenonline for correcting spelling and layout. Cheers!

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    $\begingroup$ Welcome to 3dPrinting.SE! You don't mention what filament you're using, nor what the bed/nozzle temps are. What printer are you using? Have you checked the nozzle to see if it needs to be replaced? After 650 tokens, this could actually be an issue of the nozzle being worn out .. just some thoughts. $\endgroup$ – Pᴀᴜʟsᴛᴇʀ2 Nov 30 '19 at 17:12
  • $\begingroup$ This has become a messy question, you should try to restructure it so that it is a more clear question with things you tried (more logical, chronological). SE is not a regular forum, typing out edits and updates, instead you should rephrase the question, that way it more likely attracts better answers. Hope that helps you to get the answer you need. $\endgroup$ – 0scar Jan 4 at 18:41
  • $\begingroup$ 215 seems kind of hot. What's the bed temp? This looks a bit like the plastic isn't setting up fast enough as you put down adjacent lines, so running a bit cooler might help. $\endgroup$ – Joel Coehoorn Apr 16 at 13:57
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A new day, a new nozzle, an old result!

Success

EDIT

The success was a one off. The problem remains!
Heat on the heated bed seems to differ a lot in different areas. Just using my hands to feel it since I have no IR-camera.

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    $\begingroup$ Thanks for posting your results with the new nozzle! Hope you hang around and vote! Good luck printing! $\endgroup$ – 0scar Dec 4 '19 at 18:15
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A problem I encountered a similar problem with adhesion because the nozzle was pressing straight into the bed. This made the filament squeeze out the side resulting in near zero adhesion. Check that the print bed is levelled and the nozzle isn’t obstructed by anything.

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Wait, you have your Z-height at a negative 1 mm+ offset for the first layer? After a build plate leveling? I'm surprised your extruder isn't gouging long trenches in your plate surface. Then again, this is a Prusa, they are actually capable of negative offsets from their "zero" unlike many other printers where "zero" is when the microswitch engages at the bottom of the lead screw travel.

From the description of your problem, and what you're printing, my diagnosis is improper bed prep, possibly coupled with some alignment issues. Prusas, unfortunately, fall out of adjustment almost constantly; in addition to usual bed alignment requirements, the dual lead rods have to be kept in perfect alignment at all times, which among other things means you have to be really careful manhandling the printer to get things off the build plate. Your first video shows a pretty decent extrusion line at first, with problems occurring as you get close to the front right corner, which tells me that corner is a bit low, and maybe the gantry or the entire right side of the plate is backed off too far.

Your second video has the extruder way too close. Even if you're printing a 0.15 mm or 0.1 mm layer height, that is far too thin a layer.

The bed prep, however, is likely the bigger issue. You're compensating for the layer not sticking by moving the extruder closer. That's a possible solution, but you've exhausted that as an option; your extruder's right down on the plate in that first print picture and it's still not sticking. That means the plate is dirty, which if you just spent several minutes prying tokens off the build surface, is only to be expected.

Plate surface preparation is something you need to at least look at between every single print. Some prep methods are more durable than others; I've printed dozens of prints on a single layer of kapton tape (which is good, because getting a wrinkle-free, bubble-free layer of kapton down on a non-removable print bed in an enclosed printer design like the MakerBot 2X is a real chore), meanwhile hairspray or blue painter's tape, while easy to apply, might have to be reapplied after every print.

Exactly what you do depends on the build surface and the material you're printing, but the absolute minimum you should be doing, if you print directly on your build surface with zero bed adhesive, is to clean and degrease the bed every time. A little isopropyl alcohol (rubbing alcohol) or denatured alcohol ("methylated spirits" for those speaking the King's English) is usually the thing to use, with a paper towel or microfiber cloth and a little elbow grease to really cut any grease layer on that surface.

It may well be that with this Prusa, you will have to give the plate a wipedown with denatured alcohol and then re-check the bed's calibration between every single print. Such is the nature of these RepRap-style printers, developed specifically to make 3D printing more affordable at which they succeed admirably; the tradeoff is the \$300 printers take a bit more futzing with, while the \$3000 printers are designed specifically to minimize hands-on work. But even on a \$6000 industrial printer, you have to prep the bed for each print.

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Okay so I am not an expert but I think I can help.

  • First off, your nozzle is too close to your bed. Take it up, I guess, to like between -0.75 to -0.6 mm. Play around there.

  • For not sticking part, see whether it sticks with higher bed and nozzle temperature. Higher temperature like for Nozzle: 220-250 °C and for Bed: 65-80 °C. (Yes its too extreme for PLA filaments but we are observing what happens).

  • And I couldn't make out from the video, is your print fan on? If so, switch it off.

  • I would advice to test print with a cube of dimension 200x200x0.2 mm. In your PrusaSlicer, set the Bottom Fill Pattern to be "Concentric" and your First layer height to be 0.2 mm. (I got this idea from a forum but I cannot recall its name)

  • And as mentioned by @KeithS, keeping your bed clean is important. With isopropyl alcohol and cotton balls wipe the surface. (Though don't this too many times. I have heard that the bed looses its adhesion if done so. After a couple of prints wipe with isopropyl alcohol and before every print wipe just with a kitchen towel).

  • If your bed is clean, then use glue sticks (note note all glue sticks work) on the print surface right before a print. Don't worry you can take it off after the print.

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