<p>I'm printing stacked Prusa COVID-19 face shields on a modded Ender 3. It works fairly well until the second layer of masks, where we get this weird effect that's kind of like stringing. It looks like the curve is becoming "low poly." I'm sorry that I can't be more specific, but I really don't know how to describe it more than this. Please look at the pictures to get more info. </p>

<p>One of the strangest things is that it worked earlier with the same slicer and the same profile. I am using PrusaSlicer, but I tried it with Cura and it still didn't work. There are a few more problems with the prints: some under-extrusion on the supports, and some spots had little gaps between the layers. </p>

<p>Does anyone have any fixes for any of these problems? I would mainly like to know about the strange kind of stringing because that actually prevents me from stacking prints. </p>

<p>I am printing Overture PETG at 240 on the nozzle and 80 on the bed. This is at a speed of 50 mm per second. I have the Basaraba Innovations direct drive mod, the Creality silent board with TH3D Unified Firmware based on Marlin 1.1.9, and the EZABL Pro.</p>

<p>Please look at the pictures to see what is happening.
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[{'answer_id': 13394, 'author': 'R.. GitHub STOP HELPING ICE', 'author_id': 11157, 'author_profile': 'https://3dprinting.stackexchange.com/users/11157', 'pm_score': 1, 'selected': False, 'text': "<p>Since you've said you can feel a problem at the nozzle pushing it through manually, and since you say it goes away for a while after cleaning, you probably have somewhere that molten filament is getting into that it's not supposed to, then solidifying and jamming. Check that the cooling fan for the heatsink on the coldend is working, and that the PTFE tube is properly installed all the way through the heat break and butted up against the nozzle with no gaps or irregularities, and that the pressure fitting is holding it firmly and not allowing it to back out. If you can't find anything wrong, it's possible that something is just defective/damaged inside the hotend assembly.</p>\n"}, {'answer_id': 13442, 'author': 'vale.maio2', 'author_id': 20065, 'author_profile': 'https://3dprinting.stackexchange.com/users/20065', 'pm_score': 2, 'selected': True, 'text': "<p>So, after some day of yelling and disassembling, I figured out what was the issue. As many were suggesting, I indeed had an issue with the tubing lifting from the nozzle. it was lifting, so PLA was slowly infiltrating where it wasn't supposed to be to the point it created a blockage, resulting in skipping.</p>\n\n<p>However, no amount of cleaning and reseating the tubing got rid of it. i've also changed, again, nozzle, tubing and pneumatic fittings to higher quality ones to no avail.</p>\n\n<p>I got absolutely fed up and bought a direct drive conversion kit. One of the cheap ones, reusing most of the stock hardware, including stock extruder and gears. The idea, for me, behind it was that the mass of the extruder, and the much shorter length of tubing, meant that the tubing had no space to move around and let the PLA out.</p>\n\n<p>It looks like it's working so far, I'm 6 hours in on a 10 hours print with no skipping at all. I also managed to ease the pressure that the extruder arm excise on the filament, so it's not being chewed anymore and I'm not seeing any PLA shavings so far.</p>\n"}, {'answer_id': 13446, 'author': 'Marek Urbański', 'author_id': 20819, 'author_profile': 'https://3dprinting.stackexchange.com/users/20819', 'pm_score': 0, 'selected': False, 'text': "<p>I my case helps reducing printing speed, from 100% to 80%.\nLooks like the filament is cooling noozle to fast.\nIn some large prints at the begining (on first layers) I'm reducing speed to 60%.\nThis looks like the background temperature is not the same in the center and at the borders.</p>\n"}, {'answer_id': 14228, 'author': 'Rob Atkinson', 'author_id': 23209, 'author_profile': 'https://3dprinting.stackexchange.com/users/23209', 'pm_score': 1, 'selected': False, 'text': "<p>Lot's of factors can cause this behaviour. Firstly check there are no knots in the reel - that can lead to the reel locking up. Second check the PLA temperature and if dual wall (a lot of material being put out) check that the print head is not knocking (running over the top of) excess material due to oozing. I found that after swapping out the print head HE and extruder for new, that the root cause was that I had oozing and was not using the nozzle fan. This led to the head bumping over lumps in longitudinal runs (you could hear a thud), which led to the head getting gradually backed up and the reservoir in the head back-filling with hot PLA. This then created back-pressure into the Bowden tube and then up to the extruder, which is trying to push material into an already full reservoir (head + Bowden). And.. that leads to the cog wheel in the extruder fighting against the pent up flow in the HE. The solution was to put the fan on and that stopped the ooze blobs. Because I had elected to print a fairly heavy object, the wall count was causing an excess build up and my extra-prime setting, although good for thin wall printing, together with the 6mm retract, wasn't right for thick-wall printing. So I could have turned down the extra-prime a bit, but the nozzle fan was the best and easiest option. You have to think about the whole material flow process and how the system is wired: flow-wise. It's a fancy glue gun when you think about it. So you have to be mindful of all of the parameters that can affect material flow.</p>\n<p>Having replaced the HE was actually a good idea, as I can now easily prime the head just by pushing material through by hand and feeling the flow. If you are having to push really hard, that means there is a blockage: either the head, or in the tubing or reservoir. Every two months you should maintain the printer and make sure that the head is running clear. The Bowden can also start to restrict in the head where the cleat locks onto the tubing. Heat, plus continual flexing leads to the tube starting to kink. If you are getting flakes at the extruder gear mechanism, then you have a Bowden tube or HE issue. Pushing the PLA by hand will tell you that. After a new HE is put in, you can feel the difference. A Creality 3D Pro head assembly is a few quid. I would suggest keeping a spare set of parts for maintenance work on-hand.</p>\n<p>Flakes at the extruder could also be a sure sign of water ingress in the PLA. Look for small warts or bubbles in the print. If so, put the reel in an oven at at 60\xa0°C for about 10-15 minutes. Then let cool off. Ideally you need a dry room to store reels, or a proper bucket with a drying agent inside. In the summer as heat and humidity rises, you'll notice that there's more absorption of water. If your printer is in the same room as a washing machine/dryer, you're asking for trouble. Ideally you need a dry cool space. Or just print a huge batch off and get through the reel quickly...</p>\n"}, {'answer_id': 14761, 'author': 'jburli66', 'author_id': 25260, 'author_profile': 'https://3dprinting.stackexchange.com/users/25260', 'pm_score': 0, 'selected': False, 'text': "<p>i've expirenced this a few times and just using my expirence from machining i narrowed it down to a few factors that changing fixed. #1 hot end temp, #2 axis speed, #3 filament feed rate. by playing with these settings i tend to find a happy medium with what im printing. it takes running a few set up pieces but with trial and error you can find a working point for your machine vs recommended settings. no two printers are ever the same just like no two CNC centers are ever the same. the jamming of the extruder usually is feeding too much material into the unit for its temp or it gettinng clogged at points by a bad bed level. If prints still come out ok, its pushing too much in IMO.</p>\n"}, {'answer_id': 16161, 'author': 'Dhruv Kumar', 'author_id': 28013, 'author_profile': 'https://3dprinting.stackexchange.com/users/28013', 'pm_score': 2, 'selected': False, 'text': '<p>I had the exact same issue and then suddenly it went away.</p>\n<p>The only thing I had changed was my Z-offset. I moved it away from the plate by roughly 0.1\xa0mm. To confirm it was the reason I set it back closer to the plate and the problem came back. I think When the nozzle is too close to the plate the plastic cannot freely flow out and hence the pressure develops at the feeder and it skips. This worked for me, everything is stock and no changes to the feeder settings or anything else.</p>\n'}, {'answer_id': 19385, 'author': 'Jason Fabricius', 'author_id': 34141, 'author_profile': 'https://3dprinting.stackexchange.com/users/34141', 'pm_score': 2, 'selected': False, 'text': "<p>In case anyone else also runs into this problem and has tried everything above, here is how you fix it for good.</p>\n<p>While the direct drive extruder might work, it may seem odd to some that the system that previously worked fine now doesn't and needs a complete rebuild.</p>\n<p>The problem is caused by a faulty cooling fan for the heat sink. Replace the AXIAL fan on the hotend. That is not the radial fan that is used to cool the print.</p>\n<p>The devious thing about this problem is that the symptoms occur seemingly randomly which is caused by the rather slow heat transfer in the heat sink. At some point during the print a critical temperature is reached which deforms/lengthens the heat sink and opens up gaps in the path of the filament. Those gaps cause the filament to get stuck.</p>\n<p>The other devious thing is that the cooling fan appears to be working alright but is not. I assume the rotational speed is lower than would be necessary but that can not be verified with the means currently at my disposal.</p>\n"}]
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