Random layer overextrusion "splurges"



  • I'm getting an issue on my Hypercube printer (E3D V6 hotend). On a certain layer, I'm getting massive overextrusion. It's like a pressure is building up and then all coming out at once. The extruder itself (bowden BMG clone) is still doing the correct thing, and this happens at layer heights of both 0.1, 0.2 and 0.24. Any ideas as to why this is?

    I currently use 1.5 mm retraction @35 mm/s . Filament is prusament PLA @215 °C

    alt text



  • @Dezdoghound At a first glance, this looks as if you are printing too hot. Hints: stringing and coalescing layers. In addition, PLA is hygroscopic, this could explain the „blurbs“ which you call over-extrusion. Depending on how long you already store the filament and the way you store it, you should dry it before using it again. Then, don’t be shy to reduce the temperature of your hot end, first shot with 200°C. Sometimes, PLA is even quite happy with 180°C. Finally, you can play with your part cooling fan to get better results. And please don’t withhold the photos of the results 🙂



  • @infiniteloop I don't do anything special to store this filament, so it could be that. The thing is, it happens at the same points in the print. On a benchy it's around the top of the doorway, and on another calibration print I do (retraction pyramid) it occurs in the same place too. This makes me think it could be a retraction issue?

    I'll try printing at a lower temp too, although prusa suggest 210 ± 10 °C.


  • administrators

    Does the whole layer look over-extruded? if so, are certain the the Z axis is always moving the correct amount? If your Z acceleration is set too high then it could be that the Z motor occasionally misses steps, causing the layer to be thinner than intended.



  • @Dezdoghound

    I think your heatbreak is clogging up (maybe too much retraction, or not enough radiator cooling?), then the overwhelming force of the bondtech breaks threw the clog, releasing all the material at once.

    I had the same issue with my bowden setup (therefore high retraction). I managed to solve it with a stronger (pressure oriented) radiator fan and a titanium heatbreak which I then polished internally with a drill, a fair amount of (thread / yarn?) and some whitening tootpaste ...so it was a hard issue 🙂



  • @dc42 It's not for the whole layer, and a whole load of material comes out at once when it happens. (for reference Z accel is z250 mm/s^2 and jerk is 12.)

    @denke that sounds more like the issue. The current radiator fan is a noctua 40 mm which may not be doing well enough. I'll try another fan and also do a print without retraction to see if that's causing it.



  • @Dezdoghound said in Random layer overextrusion "splurges":

    The current radiator fan is a noctua 40 mm

    I think you can find many posts on the forums about issues with noctua 40mm and e3d v6.. while quiet noctua moves way too little air to properly cool the v6's cold part



  • it depens on the noctua. there a several different ones.



  • @Veti there are several ones, the strongest one deliver less cfm than your average sunon maglev ... the 40mm noctua's are really not usable for this



  • @smece said in Random layer overextrusion "splurges":

    @Veti there are several ones, the strongest one deliver less cfm than your average sunon maglev ... the 40mm noctua's are really not usable for this

    It depends on how much space there is for air to flow through. Even the low CFM noctua can work fine if the heatsink area is not too constricted. In cases like that you may need a fan with a higher static pressure like the thicker 40mm Noctua fan. The CFM is nearly the same, but the amount of pressure it can produce with it's more aggressive blade profile allows it to push air into tighter spaces.

    In some cases it may make more sense to flip the direction of the fan so that it's pulling air through the heat sink rather than blowing it in. As long as the open side of the fan has a few mm of clearance it should be able to draw enough.

    At any rate, @Dezdoghound we need to see some more information like your config.g and your slicer settings. A sample .3mf file would be helpful.



  • @smece said in Random layer overextrusion "splurges":

    there are several ones, the strongest one deliver less cfm than your average sunon maglev ... the 40mm noctua's are really not usable for this

    it might not work for your setup, but the noctuas on the prusa mk3 are working fine.



  • I printed a Benchy with Prusament Atomic Black and got blobby layers at the same place. I printed at 205C, I think. My view is that this was still too hot for this filament, as had a bit of droop on overhangs too. I don’t think it’s any surprise that this happens at the point where the layers are much smaller, with a lot of retractions, between the pillars of the cabin.

    I’d decrease temperature and retraction distance, and make sure hot end cooling and part cooling fans are doing their jobs. Possibly even slow down the printing speed for those layers. I haven’t tried reprinting it myself yet.

    Ian



  • @Veti said in Random layer overextrusion "splurges":

    it might not work for your setup, but the noctuas on the prusa mk3 are working fine.

    they work fine where you do not need to move around a lot of air, where you have huge surface or when there's not a lot of heat that needs to be removed, but in no case they work better than a simple maglev that last longer and at same noise level push 50% more air.. noctua fan's start to have a huge benefit around 9cm and the big ones (18, 20cm) are quieter than same cfm fans of "regular brands" (there are other super quiet models from other brands too, even better, bit more expensive and not as marketed) ... I'm using noctua's since 2006/2007 as they were novelty and the only fan I could get in this god forsaken country that was nor PRC made noise generator... with all the fancy rubber "screws" and weird shaped fins... but even they started pushing below 8cm fan's only recently selling the name, not the performance



  • Ok, so I thought it could be that the airflow wasn't enough, as my current hotend design is like this with two blower fans on the side, so there isn't much room to exhaust the warm air.

    alt text

    However, I've tried some string test pyramids (https://www.thingiverse.com/thing:2219103) with one of the blowers off so there is better airflow and it always has the same "splurge" on the same layer (approx 30). The heatsink also doesn't feel noticably warm at this point, (measured 31°C).

    I've done a run of the pyramids with retraction off (pressure advance at 0.45 still on) and it comes out perfectly (minus stringing artefacts)

    I've tried printing at a series of temps and it still happened at 190°C with the prusament.

    @Phaedrux I've also attached my config.g and a 3mf file

    Things to try:

    • @Phaedrux I'll do a run with the fan flipped to see if that lowers the temp any better
    • titanium heat break when that arrives
      config_dez.g

    [0_1573682209187_string_test_fast_pyramid.3mf](Uploading 100%)



  • The .3mf didn't upload. Perhaps too large. Might have to host it on dropbox or similar.



  • @Phaedrux https://www.dropbox.com/s/7a48czp4cj1bjti/string_test_fast_pyramid.3mf?dl=0

    There's a link to the 3mf file. Let me know what you think. Don't think it's slicer related as prusa slicer does it too, although on different layers.



  • I don't see anything abnormal in the gcode file or slicer settings.

    The prusament has some glitter flecks in it, does it not? I wonder if you're getting some minor clogs and pressure build up that gets released as a blob?



  • I don't think so, as this happens with other filaments too. This is still an issue for me. I've tried disassembling and cleaning the hotend, redoing the hot tighten on the nozzle and it still happens.

    This example happened today, after doing the first layer sucessfully, it began to underextrude, then a massive splurge came out at once. It's like it's getting behind on extrusion so then trying to catch up by extruding loads?

    This happened on the second layer so there's no way it's insufficient cooling on the heatbreak. This was being printed at 215, 30 mm/s 0.12 layer height.

    I'd really appreciate any more help from anybody.
    alt text



  • What happens if you extrude continuously into free air?



  • @Phaedrux I then get a constant extrusion of plastic. It is quite a leaky extruder, but it does give constant amounts of material.


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