Issues with circles with PETG



  • So after my last issues with BL Touch and height, which I am grateful for the assistance for from this forum, i have started printing parts for the RailCore II in PETG now I have more confidence.
    Mostly the squarer parts print really well, with a couple of wisps of filament, but the bearing blocks especially where the bearing will sit are awful.
    0_1560084038315_IMG_20190609_130313.jpg
    0_1560084057121_IMG_20190609_133516.jpg
    I have done a search on this forum and checked my Cura settings, Jerk and acceleration are disabled plus other suggesstions from DC42, Phaedrux and Veti, so I think it could point towards my config.g.
    0_1560084166244_config(4).g
    but I am unsure of what needs to be tweaked to help this issue.

    Guidance and suggestions would be appreciated, please.

    Regards,

    Paul


  • administrators

    This could be related to your slicer settings. If that part is considered "internal" then the slicer may not being enabling retraction for those moves. Have a check of the retraction settings on your slicers.

    There is other stuff like tuning pressure advance that will help, but first determine if there is any retraction at all.



  • Some slicers have settings to avoid crossing perimeter whenever possible and go around instead. This may reduce the stringing in the center hole. You can also try reducing the nozzle temperature, but make sure the layer adhesion is still strong enough for your need.

    PETG is more stringy than PLA in general.



  • Hi, can you please save the project file for that part and post here (probably need to rename to zip or zip it up). Thanks.



  • I find that PETG has to be printed a bit slower than PLA or ABS. It tends to stay hot/soft longer and if you try to print small circles quickly the plastic just extruded pulls free. Slic3r lets you set lower speeds for small perimeters.



  • PETG is more prone to absorb water from the air than PLA. When I first started with PETG I was getting really messy prints so I changed brands a few times and finally found one that worked well. Then I heard about drying your filament, especially PETG. So I went back to the old stringy brands, now a year old, and dried them in my convection oven for a couple hours and lo and behold they started to print just as nicely as anything.

    My PETG profile and my PLA profiles are practically identical now. Same retraction, same print speeds, same pressure advance. All that's really different is the print temp and cooling fan. And the seam alignment is set to nearest to shorten travels.

    It's also important to have your e steps and flow rate dialed in, and measure your filament diameter. Any over extrusion is going to get stuck to the nozzle and that can create stringing and blobs of it's own.



  • As requested by @burtoogle the gcode file, hopefully I have done this right!
    https://www.dropbox.com/s/ro55nfwc8vvona0/CE3_300ZLT_Bearing_Block.gcode?dl=0

    The Cura profile I use is Phaedrux's Ender 3 profile
    I have changed it to suit as Phaedrux is clever with firmware retration etc and I am not, so put it to basics and have been printing PLA fine with it.
    I dropped the print speed to 40mm/s for PET-G, retractions are 0.8 30mm/s
    Outer Wall is 20 mm/s, Inner Wall is 40mm/s, travel was 120mm/s now 80mm/s, Fan is 30% but I turn it off as I need the strength in my parts.

    This is fresh off the printer in PET-G with a roll I was struggling with last week, the blue parts above are PET-G also, by Real-Filament

    1_1560105982875_IMG_20190609_193326.jpg 0_1560105982875_IMG_20190609_193334.jpg

    I am pleased with it apart from the stringing in the bearing hole, again.
    I think Tony may have given me an idea about the Inner and outer speeds, so I will tweak them and try and print the bearing block again tomorrow.
    I am not worried about the corners as it is very thin and I had to enable 'thin walls' to get them to print and it is not structural.

    It is just larger circles it struggles with, it seems to accelerate very fast on some actions.

    This is a Z bracket with small holes, again in PET-G, and they are fine.
    0_1560107336340_IMG_20190609_200012.jpg

    Tomorrow, I will video a badge I was printing last week which was giving me all sorts of issues.

    Thanks all for your help. I wish I could buy you all a beer or 3!

    Regards,
    Paul



  • @paulhew The place where the bearing goes, it needs support since there is a hole in the middle, which prevents the bridging from working correctly. Without support, it'll always be stringy like that.



  • Hi, thanks for the gcode file. I really wanted the project (.3mf) file but it doesn't matter. As has been pointed out, the biggest issue appears to be that the surface that has a hole in the middle that is coming out badly needs to have support beneath it.

    One setting that Cura has that is good for PETG is the fan speed override in the support section. This allows you to specify a fan speed that will be used when printing a skin over support. For PETG, you generally need 100% fan when printing a supported skin otherwise it tends to stick too well to the support.

    Looking at that model, you should be able to get away with little or no cooling fan for the rest of the print. Hope this helps.



  • Thanks again all for your input.

    Started again with E steps which were correct then onto flow rate.
    Flowrate is now at 80% compared to PLA which needs 100%!

    However it is printing better even though my first print de-laminated, increased hotend temp and it has stayed together, just forgot to put the infil back after performing flow rate test! Doh!

    Regards, Paul.


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