[SOLVED] Prusa MINI underextrusion and clogging after the first layer

by SuperheroDIY

Overall, I've loved the print quality, ease of use, and reliability of my Original Prusa MINI 3D printers. I did buy two of them, and they're printers which I like to run as often as possible, churning out fun props and parts. 

Prusa mini clogging after the first layer

Issue

That's why I was so disappointed and confused when not one but BOTH of my MINIs started underextruding, and finally just would have a clogged nozzle after the first layer! To be clear, the first layer would go down perfectly, no matter the size of the print. But once the fan kicked on and it started to move more quickly to do the second layer, I'd hear the extruder clicking and sure enough the nozzle would completely clog up.

Unloading the filament, cutting the end off, reinserting and loading the filament again cleared the clog every time. However, trying to print again the same thing would occur. 

Here's a short video of what I was seeing:

Cause

PTFE tube not pushed against heater block/nozzle, so filament is melting and bunching up outside of the tube/nozzle. Can tell by filament showing melt spot before hitting the nozzle.

Resolution

So, what fixed this? 

I contacted PRUSA Support -- and while they tried to be helpful by providing a couple links on extruder surgery and setting first layer height, they missed the mark. 

The answer was provided to me after I reached out to a user on Reddit, who very kindly shared his previous comment on the matter:

This is definitely underextrusion, and happened on one of the first first prints on my Mini, both with Prusament PLA, and Atomic PLA. Here is the Prusa page explaining how to fix the hotend. Basically, here's what you do (there's a lot of steps, this is the high level):
  1. Remove the Bowden tube and nipple from the hotend, and then remove the PTFE tube.
  2. Check the bottom of the heatbreak. Likely there will be a blob there that must be removed, like the red blob here. Heat up the hotend, insert some filament (enough to get the filament into the blob), and then cool the hotend until it reaches about 120; then do a cold pull. It should remove the blob. It's hard to see the bottom of the heatbreak though. I raised the extruder to max z and x somewhere near the z gantry, and then used an iPhone, using the z motor to hold the iPhone steady to get a good picture right down the barrel of the heatbreak. If you did everything right, you will have pulled the blob out like this. Once clear, the bottom of the heatbreak should look like this.
  3. Once the extruder is clear and cool, loosen the 3 grub screws on the right. This will allow the heatbreak to move up and down. Reinsert the PTFE tube, put the nipple back on all the way, then back the nipple of 1/4 turn. Then push up on the nozzle.heater block so that the PTFE tube is compacted between the nipple at the tope and the bottom of the heatbreak at the bottom. WHILE HOLDING IT TIGHT, retighten the grub screws.
  4. Once the screws are tight, tighten the nipple the last 1/4 turn.
Even after doing that, you may find that there's still a bad nozzle clog. It may be helpful to manually push filament through a hot nozzle, and use the needle provided to help clear the clog. If the filament is difficult to push through, or curls up excessively when coming out of the nozzle, there's still a problem somewhere. After you've done all that, you're likely to find that your live-z needs to be readjusted. If it's a big change (it will likely get more negative), it means that the PTFE was loose inside the heatbreak, which is what allows the filament to ooze into the bottom of the heatbreak and cause the clog. On my Mini, the live-z changed so much I had to move the MINDA, which tells me Prusa assembled it incorrectly.

 

Card

Once I took these steps to properly seat my hotend, heatbreak, and PTFE tube, it was back to normal! YAYAY!

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