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Issues with Top Surface using PETG


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Posted · Issues with Top Surface using PETG

Hi All

 

I am new here and relative new to the world of 3D printing.

 

I have an Ender 3 V2.

 

When I am printing pieces which are flat on the top, I am struggling to get a decent surface finish.

 

The bottom of the print is ideal, and I would like to achieve the same quality on the top, but no matter what I try, I cannot get a decent top layer.

 

The part is 2mm thick, PETG.

 

I have attached some photos to show the quality of the top surface and bottom surface.

 

Any suggestions would be greatly appreciated.

 

Thanks

2021_03_17_11_00_04_Window.png

2021_03_17_10_56_14_Window.png

2021_03_17_10_52_13_Window.png

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    Posted · Issues with Top Surface using PETG

    I see 2 issues: underextrusion, combing.

     

    1) First of all - the easy one - in the photo just above you have "strange lines in the top surface".  Those are non-retraction travel moves.  Non extruding moves that didn't do retraction.  Also called "combing" moves.  Turn off combing in skin.  combing speeds up your print significantly but makes the top and bottom layers have those lines.

     

    combing mode    set to    not in skin

     

    2) Underextrusion.  This is more complicated.  It could be you just don't have enough support.  For good support of the top layers you want about 24% infill and about 5 top layers.  Verify this is true in your settings.  Sometimes the first layer on top of the support dips down a bit and then the next layer dips into where the previous layer was (but not as much) and it takes quite a few layers until you have a layer at the right height and then the final top layer has the exact right amount of space so that you have no underextrusion.

     

    More likely your issue is mechanical - the nozzle is slightly clogged or you are printing too cold or too fast or one of about 30 possibilities.  Try just printing at half speed.  You have maybe 10% underextrusion which is pretty common and mostly only noticable on the top layers.

     

    infill 24%

    5 or more top layers

    cut all printing speeds (not travel speeds) in half

     

    3) ironing.   You can improve the top layer even more with ironing.  Invented by someone who made parts similar to yours.  Read only the neotko posts here - realize the early posts are in a different slicer (S3D) -he is the world expert on ironing since before it was an option in Cura - there's 3 pages of posts to read so only read the neotko posts:
    https://community.ultimaker.com/topic/15213-neosanding-automatic-layer-sanding/

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    Posted · Issues with Top Surface using PETG

    Oh I missed the "milky" thing.  I don't know what that is.  I can't really see it in your photo.  It might be temperature related?  I'm not familiar with this issue.  I thought I'd seen every possible complaint about print quality but this is a new one for me.

     

    Oh - PETG.  It could also be water in the filament.  Maybe dry the filament before printing.  PLA doesn't have any issues with water absorbtion but I seem to remember that PETG does.  Read about how people dry filament using the heated bed.  Caution - don't melt/ruin your filament nor spool.  PETG can be melted at temperatures as low as 80 or 90C.

     

    Black glossy is the absolute best material for showing defects.  Consider other colors.  The combination of a dark color and the shiny surface lets you angle the part to the light just so.  Such that you can see glints that show off tiny, normally invisible defects.  Unfortunately, matte colors are rare in 3d printing and usually involve some kind of infill like sawdust or chalk.

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    Posted · Issues with Top Surface using PETG

    Also, printing in thinner layers normally gives a smoother surface. But twice as thin takes twice the time to print...

     

    These blocks are in PET, printed at 0.10mm and 0.06mm.

    DSCN6022.thumb.JPG.a72e3faf1f92cb1f2b61ed08edd6a101.JPG

     

    The green model on the top right is in PET too. It's hard to see here, but the surface is quite smooth, letting a hollow watermark text shine through. Note that this model is small, see the ruler in mm and cm below. The red object shows 50% underextrusion (was part of an underextrusion test).

    microscope10.thumb.png.f19ba929a276abe9c32cc4b0c807b4c9.png

     

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