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Solved PETG zits.

Discussion in 'Troubleshooting' started by Oisin, Dec 21, 2016.

  1. Oisin

    Oisin Member

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    Hi guys.

    Does anyone use PETG filament? I love the way it looks but I've been struggling to get rid of these 'zits' that I assume are caused by retraction or layer changes. I would like to know what effects retraction distance and speed have. Would a higher retraction distance and speed help? Maybe more of one than the other?

    Here is what I have tried:
    1) Coasting 0.2mm, Wipe extruder, Retraction rate 120mm/s, Retraction distance 1.5mm
    2) Retraction rate 120mm/s, Retraction distance 1.5mm
    3) Retraction rate 400mm/s, Retraction distance 1.0mm

    I would love to get smooth prints from this material. I don't really know what parameters would be most effective in removing these 'zits'.

    I've looked this up and tried to implement some of them with no success. I'm printing at 25mm/s and 235C at 0.1mm layer height.
     

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  2. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    In my experience with PETG, those zits are the result of a very slight over-extrusion and the fact that PETG has trouble sticking to anything other than PETG. So lower your extrusion multiplier by a thousandth or two or three.
     
  3. Oisin

    Oisin Member

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    Ah I see. I was printing on 0.99 extrusion but I'll knock it down some. Can you explain the pattern, out of interest? There's a distinct diagonal line of zits on each blade of the fan.

    Reducing the multiplier will mean surfaces are not fully intact.
     

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    #3 Oisin, Dec 21, 2016
    Last edited: Dec 21, 2016
  4. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    Probably where there is a filament retraction. or the start of every layer for that particular perimeter. Hard to say without actually seeing it print.
     
  5. Oisin

    Oisin Member

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    Well what I've done is I've changed the settings to use the same point for layer changes. Raised the print speed to 50mm/s and increased retraction to 2mm. I've also reduced the extrusion multiplier to 97%. It's still making the blobs. This seems to be a common thing with PETG.

    I looked at getting translucent red PLA from rigid.ink. Unfortunately rigid.ink is twice as expensive as regular PLA from 123ink.ie.
     
  6. Geof

    Geof Volunteer Moderator
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    PETG loves to ooze and build up on the nozzle. That is typically what causes alot of blobs. Calibrate your extruder for PETG if your going to print with it often, if your not....mess with the flow until your prints look good but not over extruding. I havent used it in a very long time so I cant help very much but that is where i started to get rid of the blobs and charred bits.
     
  7. Oisin

    Oisin Member

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    I've changed the extrusion multiplier down to 90% and strangely the prints are identical to the usual 99% multiplier prints I do. This doesn't occur at 0.2mm, but I never print with that layer height anyway.

    I guess I'll just keep reducing the multiplier. Flat surfaces will not print properly though.
     
  8. Geof

    Geof Volunteer Moderator
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    the flat surfaces should print fine if the issue is overextrusion :D. If its not, then we move on to the next issue and resolve it. Have you cleaned the nozzle very well? its possible left overs on the nozzle are dropping through the next prints.
     
  9. Oisin

    Oisin Member

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    Fair enough. I just remember dropping the extrusion multiplier a long time ago and seeing surfaces come out hatched.

    I dropped it percent by percent down to 80% and it did not change. Surfaces began to break up as expected, but the zits remained. My extruder was calibrated to begin with, with 100mm in Octoprint extruding exactly 100mm of filament. Does PETG suffer from water absorption the same way PLA does? Bubbles in PLA can be explained by water, but these zits just break off when you scratch them. Not the same.

    The nozzle is clean and I haven't had the issues of burnt PETG being deposited on the print like other people have seen.
     
  10. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    Take your multiplier back up until your flat layers are solid again. then try increasing your speed just a bit. If you are printing PETG at 40 mm/s try 45 mm/s, 50 mm/s try 55 mm/s. Be careful how you input the value since some slicers (including S3D) are stupid about mixing mm/m and mm/s in different dialog boxes. Just remember if you understand a value as mm/s but the program wants mm/m then multiply what you expect by 60 to get the correct input value (example: 45 mm/s == 45 * 60 mm/m == 2700 mm/m).
     
  11. Oisin

    Oisin Member

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    I increased my speed from 25mm/s to 50mm/s in increments of 5. The higher speeds generally saw a decrease in quality. Thanks for the tip, Waldo! I'm going to try 4 different processes on 4 different iterations of the same model in S3D and see if that will let me test quicker. Not sure how the printer handles that or if it will actually change settings for each model.
     
  12. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    Yes it works, I just did the same thing and printed layer by layer, you also have the option of printing them one at a time.
     
  13. Oisin

    Oisin Member

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    Okay good. I printed one at 0.2mm just to see. It came out much cleaner but still with some zits. The corners were much nicer too. Overhangs were poor though. I exclusively print in 50 and 100 microns since they look so much nicer. Might have to make an exception until I can get some PLA.
     
  14. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    You print opposite than I do, I print almost everything at 0.25 mm layers unless there are overhangs. If the angle is steep then I might print them at 0.2 mm layer height. A few things, very few, I print at 0.1 mm height and nothing at 0.05 mm. I also print faster than you are, I don't have a single filament that I print under 60 mm/s.

    If it is something I have never printed with before and I need to 'learn' how to print with it, I will start out around 40 mm/s, but once it is dialed in for temp and extrusion multiplier and overlap, etc, the speed is bumped up until it starts to really look bad then I back it down just a bit. But I also tend to print on the higher end of any range I have found and I print on the high end of hot.
     
  15. Oisin

    Oisin Member

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    I'd love to be able to print that fast! I always aim for maximum quality, hence the 25mm/s and 50 microns. It doesn't bother me how long something takes.

    PLA prints terrible overhangs for me. No more than 30 degrees and that's at minimum nozzle temp and two 40X20mm fans on 100%. PETG can originally printed overhangs very nicely but at the moment it's not. Couple that with the zits and I'm questioning the filament itself. The filament is only a month or two old. Maybe it's just 'gone bad'?
     
  16. WindDrake

    WindDrake New Member

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    I ran 28 parts in 3DXStat PETG yesterday, all zit-free. Bone stock R1+.

    In Mattercontrol, I reduced the retraction rate to 25mm/sec, and ensured that the "External Perimeters First" was unchecked, so it tucked the layer changes into the model itself. Otherwise, I was running the standard 60mm/sec print speeds, 0.2mm layers. 250*C hotend, 80*C bed.
     
  17. Oisin

    Oisin Member

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    Interesting, WindDrake. I see in my settings that models already print from the inside out. I'll try reducing the retraction speed. I've ordered some PLA filament. If this occurs with the PLA then I'll know it's a problem with the nozzle and not the PETG.
     
  18. Oisin

    Oisin Member

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    I printed a very large part consisting of straight edges only and it printed flawlessly. There's something about the propellor blades geometry coupled with the extrusion that's causing the zits. Very odd.
     

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