Randomly under extruding and clicking
Just got my MINI and the first print was beautiful. But now it's giving me nothing but trouble. It will start printing fine but after a few minutes the extruder drive gear just starts grinding on the filament and clicking. The first time that happened it was so bad I had to take the bowden tube off completely and pull the filament out with a good deal of force. But since then if I catch it I can usually use the "Unload" option and it works fine. And I've tried pushing filament directly through the extruder with the bowden tube off and it works fine - so there's no clog there.
I've also followed the KB guide for MINI extrusion problems and adjusted the idler tension both tighter and looser than how it was when it came to me to no effect. It keeps grinding and stops extruding after a few minutes. Can't really see well, but since it has an idler wheel I'm guessing it's not a dual side drive like on the MK3? That's a shame 🙁
While a bit different I followed along here: https://forum.prusaprinters.org/forum/assembly-and-first-prints-troubleshooting/underextrusion-4/
I did actually notice that my heat break was sticking pretty far out from the heat sink so I loosened the 3 grub screws (which oddly required a 1/16" hex not a 1.5mm... wtf?) and pushed it further up into the heatsink. Then, of course, moved up my PINDA probe and redid the first layer calibration and z offset.
After that I was able to get a little further - ALMOST finished the whistle print before it starting failing while doing the very top bridge - that was the first time during that print that I heard the extruder gear start to click and that top layer is just a gross mess.
I love my MK3S but pretty disappointed so far with this MINI - I've literally never had any issues with the MK3S.
Don't only move hot end up, if there's melted plastic inside that leaked out of some gap, it's not going to help you. Do a little more disassembly and inspect innards. Unmount Bowden tube from the top, unscrew coupler, pull out PTFE tube, shine some light and look down the hole. There should be no plastic at the bottom, only shiny metal. To remove plastic from place it should not be, user PJR here suggested to heat nozzle to PLA temperature, insert a stick of filament down there and collect it. Also measure PTFE tube length - it should be 43.4 mm plusminus. Here is a guide on how to properly assemble and tighten hotend: https://manual.prusa3d.com/Guide/How+to+change+a+hotend+PTFE+tube+-+MINI/1505?lang=en
Here is guide on hotend disassembly if you need to clean or change it further: https://manual.prusa3d.com/Guide/How+to+change+a+heaterblock-heatbreak+-+MINI/1511?lang=en
I did pull out the PTFE tube and looked down in there and it was all clean - didn't measure the tube but I can do that. It really feels like it's getting bound up in the bowden tube. With that tube off I've noticed that filament has a lot of resistance when passing by those little brass pieces on the tube - no idea what they are called.
Also, I ran another test late last night and was able to quantify something a little better since I was watching closer.... when printing the whistle, on the early layers I'd hear a couple clicks and some lines would under extrude. But then later on that layer it's as if there had been backed up pressure on the filament and it all of a sudden WAY over extrudes on a few lines. Making a bit of a hump in that section of the layer. Not sure if that helps.
I'll tear down everything again tonight or tomorrow for good measure. Just really wish I didn't have to on a brand new, mostly pre-assembled printer 🙁
... user PJR here suggested to heat nozzle to PLA temperature, insert a stick of filament down there and collect it...
I revised my method as I didn't really have much luck doing that. But this was the method advised by PR staff.
Instead, I used a battery powered drill with a 4mm bit. Carefully though as it is possible to damage the inside of the heat break. All you need to do is to loosen the plastic and it will drop out.
Thanks for correction. I knew you wrote something about fishing out plastic out of there and it stayed at the back of my mind for some reason. I guess the metal surface does not hold to plastic very much and it will go out easily.
Ok - So I tore things apart again and found a few things:
- The stock PTFE tube that came in the machine was 41.2mm not 43.4mm 🙁 Fortunately the spare is the right length
- I did a cold pull and it did, in fact, pull a bunch of gunk out of it - which makes sense since the PTFE tube was too short. Also, it seemed to pull out a small piece of metal. Just a tiny shaving - but that's not good.
- Last and definitely the worst - I decided to do a second cold pull for good measure and followed the instructions exactly - but when I pulled the filament just snapped off and now there's a big old blob down the bottom of the tube. I've tried 3 times now to heat up again, push the filament in, let cool to room temp, then back to 90-100C and pull.... but every damn time, the filament snaps off. So I am 100% dead in the water now. How do I get that filament out?? I'm a bit afraid to try the above anymore in case it's just adding more melted filament to the problem 🙁 It's not like I'm a newb to this... this is my 4th printer. I've never had this much trouble with any of them. But unless there's some trick to getting that blob out I may need a new extruder assembly.
Have you tried higher temperature to make plastic more liquid? Stick acupuncture needle from bottom to release clog, it may help making it flow out and release biggest blob.
What filament you use for cold pulls? You can try something like nylon which is more elastic and sturdy. Cleaning filaments are good too if you don'thave or want full nylon spool. Desregard if you already use it.
Rather than buying whole hotend, you can strip existing one to nozzle, heatbreak, aluminum block and heatsink. It makes it easier to clean individual parts. I bet there's plastic somewhere between, forming ring or bulge which makes it too thick to pull through PTFE.
All I had on hand was PLA - I've got some nylon on the way just in case. Chatted with Prusa support last night and their suggestion was to tear down the hotend so I can push the blockage out from the bottom. So I'll give that a try later today.
And wasn't trying to cold pull through the PTFE - the official instructions for it actually say to remove the PTFE tube first and then do it.
Right, for some reason I thought you have PTFE stuck there as well and cannot pull it out.