2 Issues: impossible to do a cold pull on my MK3, and terrible second layer troubleshooting.
I apologize for the long read, but I have 2 separate issues that may be linked in their causes and results so I'm writing up both here with as much background as possible in case there may be a connection.
Some background info: I've been using my pre-assembled MK3 for printing the products I design and sell since Fall of 2018, I print around 40 hours per week on it. I replaced my Hotend for the first time in late 2018 when faulty insulation caused a short on the heater block and also melted my bowden tubing due to the irregular temps. My 2nd hotend failed after about 2 months of use due to heat break clogging issues. A few other users of the old forum mentioned heat break manufacturing defects around that time , so I replaced everything except the heatsink and heater block with plated Microswiss parts and capricorn tubing.
Since Spring of this year my Mk3 has been almost flawless in print consistency with regular maintenance. I use only PLA and calibrate regularly when trying new brands.
Cold pulls have been often recommended for clearing various filament and nozzle related issues, but when I try the official guide here https://help.prusa3d.com/article/lnbcnhg76k-cold-pull
It never works, it just snaps cleanly somewhere higher up (likely in the heat break based on the length i pull out) and the filament doesn't get hot enough to move at all through the nozzle, even with pliers as recommended. I've tried with multiple brands of PLA I use regularly. Would heating it up beyond the recommended 85 degrees still have any sort of of the same benefits? My MK3 was delivered fully assembled by Prusa around March of 2018, and I've had to replace and upgrade several hotend components before I've had it become my most reliable printer starting in 2019. My firmware is the latest version.
The article says nylon is a possibility but it also says PLA should work fine. I'm curious why mine doesn't pull at all with pliers, and I've tried with official Prusament PLA following the guide step by step. All filament just does a clean flat snap a few centimeters above the nozzle.
As for my second issue, I'm attaching a photo, my first layers are fine after 5 test prints, but once the second layer starts there's terrible extrusion issues. The model in question I print is one I sell regularly so I usually print 4 parts per week, two 17 hours prints and two 7 hours prints. These prints have worked fine for the past 7 months or so. It must be some new wear issue with my suspicions lying with either hotend (bowden, heatbreak, nozzle) or filament, although filament is unlikely as I'm using the same spools I've used regularly and keep free of moisture. No settings were changed before this started.
I'm doing all of this since my 2nd layers have started suddenly having terrible extrusion issues after weeks of flawless prints. with no changes files, filament, or environment to be an obvious culprit, leaving me with hardware issues as the likely cause. Perhaps of you have had similar experiences and have found fixes
Steps I've take so far to try to fix this:
- Z axis and first level calibration seemed the most obvious, so I've gone through those processes several times.
- Updated to the newest firmware
- Replaced the nozzle and bowden tubing twice with new parts, each time following the official Prusa guidelines for re-assembling the nozzle, bowden tubing, heatbreak, and heatsink. I had to tinker with the heatbreak and tubing several times in the past so I've bought a stock of spare parts for occasions like this
- Re-calibrated the location of the Pinda sensor several times as needed when I replaced nozzles
- Full XYZ, first layer calibration, and mesh bed leveling between each relevant change
- Tried 3 different brands of filament I know I've used successfully in the past
- Tried printing new flat sample models
- Changed temperature to see if higher/lower affects print
- Cleaned Extruder gears (there's rust colored residue in there but not on the gears, just the black housing)
- Checked for blockages/dirt in hotend, fans, and around all motors, rods, and belts
- manually confirmed temperatures using IR thermometer
- Used acupuncture needle to check for nozzle irregularities
- Yelled at the printer
Thank you for reading, any suggestions are appreciated, I would like to see if there are any other options out there before I spend over $80 plus shipping on my third Prusa hotend assembly, since nozzle, bowden, and even heatbreak changes just don't seem to be cutting it at this point
RE: 2 Issues: impossible to do a cold pull on my MK3, and terrible second layer troubleshooting.
Rather than cold pulls try using cleaning filament.
I use this every time I go from a hotter filament like PETG to a cooler one like PLA. I have been happy with the result so far.
RE: 2 Issues: impossible to do a cold pull on my MK3, and terrible second layer troubleshooting.
PLA softens very quickly at relatively low temps, so can be difficult to get a good cold-pull result with. As @rober-rmm200 notes, cleaning filament is a good alternative. It melts at a wide-range of temps, so you can clean things out at 265C but know that anything left in the nozzle will melt out next time you print with PLA at 200C. Left-over higher-temp filament is a major cause of partial blockages such as you seem to be experiencing.
Here's the process I use for cold pulls:
- Raise Z
- Set temp to whatever is appropriate for the currently-loaded filament
- Unload existing filament
- Set temp to 265C
- Load cleaning filament
- Extrude filament for 3 cycles (reply "NO" to message twice) to ensure nozzle is cleaned
- Reset nozzle temp to 0C and let cool with cleaning filament still loaded and some extruded
- Open extruder to remove tension
- Grab cleaning filament with pliers
- Set nozzle temp to 200C
- As nozzle temp rises, brace extruder to avoid twisting and pull gently straight up with pliers
At somewhere between 90 and 120C, the filament should pop out hopefully showing the inner hotend geometry. Upon removal, you should be able to see light through the nozzle opening.
I do this whenever I suspect a partial jam, and whenever switching from higher-temp materials (e.g. PETG) to lower-temp materials (e.g. PLA).
RE: 2 Issues: impossible to do a cold pull on my MK3, and terrible second layer troubleshooting.
@bobstro
Thank you for your explanation about how to use the cleaning filament, do you have a specific brand you'd recommend? eSun is one of the first brands that pops up on amazon and seems to have decent reviews, I'd like to know what brand you used to get those results, thank you.
RE: 2 Issues: impossible to do a cold pull on my MK3, and terrible second layer troubleshooting.
Thank you for your explanation about how to use the cleaning filament, do you have a specific brand you'd recommend? eSun is one of the first brands that pops up on amazon and seems to have decent reviews, I'd like to know what brand you used to get those results, thank you.
eSun is very good. It's nice and stretchy, so well suited to popping out without snapping. I really liked rigid.ink, but they're getting out of the filament business. rigid.ini's cleaning filament is more brittle and stringy -- I hate the fine threads it makes -- but it has the property of absorbing a lot of moisture. While that's a bad thing for filament, it's great for cleaning filament in that it comes out steams and frothy, so creates a bit of a scrubbing action that works well.
RE: 2 Issues: impossible to do a cold pull on my MK3, and terrible second layer troubleshooting.
Bob, looks like you are courting a filament jam based on the images above. The top pull has the very clear 1.75 > 2.2 > 2.0 step, and you can even see fresh melt popping out of the hot zone in the second pull.
RE: 2 Issues: impossible to do a cold pull on my MK3, and terrible second layer troubleshooting.
Bob, looks like you are courting a filament jam based on the images above. The top pull has the very clear 1.75 > 2.2 > 2.0 step,
That was my old original (April 2018) Prusa heatbreak. Never had a jam with it that fits the retraction/heat-related scenarios. Those pics are something like 6 months old, so if something is "imminent", it's taking its sweet time about it!
I'm not overly convinced the 2.2mm step implies an automatic jam-fest. I've done retraction-intensive prints with that heatbreak without issue. This was done with a 0.25mm nozzle and 0.04mm layer heights using a jam-inviting marble filament:
I suspect the step is one of many factors that, under certain conditions, can trigger a jam. I am not convinced simply using a stepped heatbreak is the sole cause.
and you can even see fresh melt popping out of the hot zone in the second pull.
I'd expect it to given the steady slow pull out of the hot zone whilst heating! It would be hard to get a cold pull without it popping out.
RE: 2 Issues: impossible to do a cold pull on my MK3, and terrible second layer troubleshooting.
@bobstro
I received the esun cleaning filament and followed your steps. I haven't used anything besides PLA since I got this extruder so I wasn't surprised to not see any other colors or particles on the piece that I pulled out. I could see the light through the bottom of the nozzle by looking through the top, However, my issues with extrusion persists despite no changes being made when these problems started. Below is what my pull looks like., the surface doesn't seem as smooth as your images (although stepped, yours seem have a very smooth uniform surface, while mine looks slightly textured to me). This one was after the second pull I did, I did 2 just to be thorough. Edit: also like to mention this is on a brand new nozzle, and I just noticed that mine has a flat tip with a little tail rather than a nozzle shape end like yours
