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Hugly perimeters and brittle parts of piece  

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gregsaun
(@gregsaun)
Trusted Member
Hugly perimeters and brittle parts of piece

Hi All,

I need your help with a strange print I had yesterday. Bottom of the print is good but the top is very hugly. I checked the printer when it was printing those hugly parts and it is like it was inverting external perimeters with infill: it was going very fast on the external perimeter and very slow for the infill. The hugly part is very brittle but the bottom is as strong as expected.

Here are some parameters I used:

  • Slic3r Prusa Edition 1.36.2

  • 0.3mm layer height (based on 0.35 profile)

  • Extrudr MF-PETG, profile based on this settings: http://shop.prusa3d.com/forum/print-tips-slic3r-settings-kisslicer-model-repair--f12/filament-tip-extrudr-mf-petg-1-75mm-t4541.html

  • 210°C hotend, 80°C bed

  • I used "Layer editing" to increase quality on top thread

  • Infill pattern: cubic at 20%

  • 30-40% fan but I don't know why I saw the fan at 100% in the printer's menu

  • printed horizontally in the middle of the bed (to limit moves in Y, more noisy)

  • Print launched with OctoPi (and I checked state regularly with android app Printoid)






  • Thank you in advance for your help 😉

    Bear Upgrade Frame for Prusa

    --- thingiverse.com/pekcitron --- patreon.com/gregsaun --- ekunn.com

    Posted : 02/09/2017 11:43 am
    JeffJordan
    (@jeffjordan)
    Member Moderator
    Re: Hugly perimeters and brittle parts of piece

    210°C hotend temperature seems to be fairly low for PETG.
    personally I print my PETG @ 240 - 255°C.

    furthermore I recommend to set the seam position to "aligned", not to near or fastest.

    beside the tall pillar, the top end with the treads and the bottom with the base looks fairly good.

    dem inscheniör is' nix zu schwör...

    Posted : 02/09/2017 12:52 pm
    gregsaun
    (@gregsaun)
    Trusted Member
    Topic starter answered:
    Re: Hugly perimeters and brittle parts of piece

    Thanks for your reply. I know temperature sounds low for PETG but on the extrudr.eu website they say 205°C as recommended temp. I didn't remember but I think I saw another brand of PETG with such low temp. https://extrudr.eu/collections/petg/products/extrudr-mf-petg-black

    I have seen this "aligned" parameter and that make sens for cleaner perimeters. Do you think it can also solved the fact that the external perimeter is done much faster than the infill?

    Bear Upgrade Frame for Prusa

    --- thingiverse.com/pekcitron --- patreon.com/gregsaun --- ekunn.com

    Posted : 02/09/2017 2:02 pm
    gregsaun
    (@gregsaun)
    Trusted Member
    Topic starter answered:
    Re: Hugly perimeters and brittle parts of piece

    FormFutura HDGlass is also very low in temp for a PETG (195-225°C) : https://www.formfutura.com/shop/product/hdglass-blinded-black-226?category=164

    Bear Upgrade Frame for Prusa

    --- thingiverse.com/pekcitron --- patreon.com/gregsaun --- ekunn.com

    Posted : 02/09/2017 2:09 pm
    AJS
     AJS
    (@ajs)
    Noble Member
    Re: Hugly perimeters and brittle parts of piece

    I think you really need to slow down the print on the small parameter parts.

    Think of it this way, there is not time for plastic to cool properly when the nozzle is back on it again printing hot stuff onto gooey stuff. That is why your small pillar looks bad, but the larger (more time to cool) base looks fine.

    For Slic3r, under Filament -> Cooling -> Cooling thresholds there are two parameters "Slow down if layer print time is below" and "Min Print speed."

    These should help.

    See also:

    http://shop.prusa3d.com/forum/print-tips-slic3r-settings-kisslicer-model-repair--f12/trouble-printing-m10-bolt-thread-t5710.html

    Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage or loss. If you solve your problem, please post the solution…

    Posted : 02/09/2017 5:40 pm
    gregsaun
    (@gregsaun)
    Trusted Member
    Topic starter answered:
    Re: Hugly perimeters and brittle parts of piece

    Hi All,

    Sorry for late answer and thank you for your help 😉 . I could finally print correctly this piece playing with the "Slow down if layer print time is below" and "Min Print speed" parameters. I set "Min Print Speed" to 5mm/s and "Slow down if layer print time is below" to 35 seconds.

    However, I had to slow down the external parameters in the Print settings -> Speed -> Speed for print moves menu. After experimenting several similar cases, those two parameters doesn't affect the external perimeter speed (it is going faster when printing the external perimeters than internal perimeters or infill). Have you ever heard about this issue?

    Bear Upgrade Frame for Prusa

    --- thingiverse.com/pekcitron --- patreon.com/gregsaun --- ekunn.com

    Posted : 25/09/2017 10:28 am
    Vojtěch Bubník
    (@vojtech-bubnik)
    Member Admin
    Re: Hugly perimeters and brittle parts of piece

    > However, I had to slow down the external parameters in the Print settings -> Speed -> Speed for print moves menu. After experimenting several similar cases, those two parameters doesn't affect the external perimeter speed (it is going faster when printing the external perimeters than internal perimeters or infill). Have you ever heard about this issue?

    Frankly I don't quite understand what you mean. Do you think there is an issue with how Slic3r handles the printing speeds? If it is the case, would you please create an issue into the issue tracker and describe as much detail as possible, so I can reproduce your problem?

    https://github.com/prusa3d/slic3r/issues

    Thanks, Vojtech

    Posted : 04/10/2017 3:45 pm
    gregsaun
    (@gregsaun)
    Trusted Member
    Topic starter answered:
    Re: Hugly perimeters and brittle parts of piece

    Thank you for your reply and sorry to ne be clear enough. I finally found someone that raised the issue I have tried to describe on alexrj/slic3r repo. It is better described and done deliberately :
    https://github.com/alexrj/Slic3r/issues/4070

    Bear Upgrade Frame for Prusa

    --- thingiverse.com/pekcitron --- patreon.com/gregsaun --- ekunn.com

    Posted : 04/10/2017 4:15 pm
    jhoff80
    (@jhoff80)
    Trusted Member
    Re: Hugly perimeters and brittle parts of piece

    In my experience, PETG has been really brittle (bad layer adhesion) unless I disable the fan for the print.

    Posted : 04/10/2017 5:24 pm
    Vojtěch Bubník
    (@vojtech-bubnik)
    Member Admin
    Re: Hugly perimeters and brittle parts of piece

    > 0.3mm layer height (based on 0.35 profile)

    What nozzle do you use? 0.4mm diameter?
    0.3mm layer height is quite a lot. With 0.4mm diameter nozzle, the 0.35 profile is quite a hack.

    > 210°C hotend, 80°C bed
    Likely too low for PETG.

    > Infill pattern: cubic at 20%
    You may try to switch to a grid infill. The cubic infill may lay down multiple strands of filament one over the other along the inner perimeters, which for a tiny or narrow infill may cause the infill to bulge the perimeters outside, making the infill pattern visible. This will be fixed in Slic3r one day.

    Actually your issue may really be caused by a too low extruder temperature for PETG. With a too low extrusion temperature, the viscosity of the extrudate is too high, requiring an excessive nozzle pressure for a continuous extrusion. In that case the rapid changes of extrusion rate due to the cooling slow down on internal perimeters versus not slowing down on the external perimeters may cause the print defects you are experiencing. Also it seems to me that your layer adhesion is low, indicating a low nozzle temperature.

    Posted : 05/10/2017 10:48 am
    Carsten
    (@carsten-2)
    Estimable Member
    Re: Hugly perimeters and brittle parts of piece

    Excuse me if it was already asked:

    Did slic3r report any errors on the Object? I think it can get confused by wrong normals on the mesh and then print outside as inside which might explain the reverse in Perimeter speeds.

    Carsten

    My Prints: https://www.prusaprinters.org/social/15695-carsten/prints
    My Employer: https://make-magazin.de

    Posted : 05/10/2017 11:43 am
    richard.l
    (@richard-l)
    Member Moderator
    Re: Hugly perimeters and brittle parts of piece

    0.3mm layer height is quite a lot. With 0.4mm diameter nozzle, the 0.35 profile is quite a hack.

    Some of us have been saying for years that this profile shouldn't be used. If you are agreeing, why is it still included?

    Posted : 05/10/2017 3:45 pm
    gregsaun
    (@gregsaun)
    Trusted Member
    Topic starter answered:
    Re: Hugly perimeters and brittle parts of piece


    > 0.3mm layer height (based on 0.35 profile)

    What nozzle do you use? 0.4mm diameter?
    0.3mm layer height is quite a lot. With 0.4mm diameter nozzle, the 0.35 profile is quite a hack.

    > 210°C hotend, 80°C bed
    Likely too low for PETG.

    > Infill pattern: cubic at 20%
    You may try to switch to a grid infill. The cubic infill may lay down multiple strands of filament one over the other along the inner perimeters, which for a tiny or narrow infill may cause the infill to bulge the perimeters outside, making the infill pattern visible. This will be fixed in Slic3r one day.

    Actually your issue may really be caused by a too low extruder temperature for PETG. With a too low extrusion temperature, the viscosity of the extrudate is too high, requiring an excessive nozzle pressure for a continuous extrusion. In that case the rapid changes of extrusion rate due to the cooling slow down on internal perimeters versus not slowing down on the external perimeters may cause the print defects you are experiencing. Also it seems to me that your layer adhesion is low, indicating a low nozzle temperature.

    Sorry for late answer but I took the time to test few parameters on several prints as well as tower test (for temp) and I have now switched to 225°C. Going higher seems to only add stringing. I have not used the 0.35 profile since your comment. My prints are clearly better and stronger. In conclusion, my main issues were printing too fast and with a too low temperature. Thanks again for the help 🙂

    However, I am still not convinced by there explanation here : https://github.com/alexrj/Slic3r/issues/4070 (mentioned previously). I understand that a different speed might change the look of the external perimeters but that depends on the filament type. Plus, even if the color might change a bit that doesn't mean the print looks ugly, maybe even the opposite!


    Excuse me if it was already asked:

    Did slic3r report any errors on the Object? I think it can get confused by wrong normals on the mesh and then print outside as inside which might explain the reverse in Perimeter speeds.

    Carsten

    The difference in speed is due to that : https://github.com/alexrj/Slic3r/issues/4070


    0.3mm layer height is quite a lot. With 0.4mm diameter nozzle, the 0.35 profile is quite a hack.

    Some of us have been saying for years that this profile shouldn't be used. If you are agreeing, why is it still included?

    I agree with this, or at least we should have a warning somewhere in the profile (title?) that this one is kind of hack

    Bear Upgrade Frame for Prusa

    --- thingiverse.com/pekcitron --- patreon.com/gregsaun --- ekunn.com

    Posted : 25/11/2017 3:31 pm
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