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First Layer Gouging


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Posted · First Layer Gouging

Recently figured out an issue that I was having with a print.  On the first layer, when the print head is moving to a new start position across the already laid down filament (PLA) it's "gouging" into that part of the print causing some very apparent scaring.  The second layer will cover it up to a certain extent, but the scar remains.  If you preview the gcode through Cura, you can see exactly where it moves across the print.  Is this something that can be prevented?  Also, the very center of the first layer goes back to a ZigZag pattern instead of staying concentric.  I'm running the latest version of Cura.  Pics show the first layer of the print and a closeup showing some of the problem areas.  Also attached is the gcode and stl for the file.


Any ideas?





Scan 1.png

Screenshot 2021-10-18_21-54-02-449.jpg

0.24 initial height.gcode profile.curaprofile top ring holder.stl

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    Posted · First Layer Gouging

    "Why isn't this line concentric instead of zig-zag?"

    The remaining center portion is not an exact "line width" wide and so a full line won't fit.  Cura fills it instead with a zig-zag pattern.  Remember that there are no circles, only shapes defined by a lot of chords.  The cross section therefore isn't 5.00000mm but varies according to how the chords are laid out which is a function of the triangles in the STL file.  The higher the resolution of the STL file means more triangles and the closer a model is to a circle, until you bump into Cura's Maximum Resolution setting in Mesh Fixes.


    The first image is "Bottom Pattern Initial Layer = Concentric" and "Line Width = .4" with "Fill Gaps Between Walls = Everywhere".




    This one is with "Fill Gaps Between Walls = Nowhere"



    This one is with the Line Width = .37 (picked by experimenting).




    That bottom image can also be achieved by changing the Wall Thickness to 2.8.  With the current version of Cura it's always a matter of "how much room is left to fill?".



    The Cura Arachne version will vary the line width automatically to get rid of problems like that.  If you search around here there is a link to the Beta version of Arachne.  With the Line Width in Arachne at .4 you get the same pattern as that last image.


    Are you using Z-Hops?  If the retractions are set to occur over short moves then the nozzle should move up and not scuff the print.  Z-Hopping has it's own drawbacks but generally will eliminate scuffing.

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