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Inaccurate cura slicing


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Posted (edited) · Inaccurate cura slicing

Hello Cura Community.

I hope someone can provide some insight to the following issue. I have the STL file here and both gcodes. With the object laying up and the object laying flat. Somehow, with the object laying up, Cura introduced a layer shift that is not present in the STL file. Also when sliced with the object laying flat, there is no such discrepancy. I have checked and tried various options but nothing seem to remove this issue. I would think that at iteration 4.8.0 (Cura with its constant development of features and upgrades), would not introduce unwanted features/or rather features that are not designed onto the sliced model. 😞

The inconsistency/layer jump/additional feature is introduced at layer 125 in the gcode file of the object sliced laying up.

Also, the preferable print method is of course with the object laying up as no supports are necessary in this mode.

Thank you.

PartB_up.gcode PartB_flat.gcode PartB.STL

Edited by benspawn
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    Posted · Inaccurate cura slicing

    Thank you for your file. If you change horizontal hole expansion to 0 the gap isn't there anymore. 


    Layer 124:



    Layer 125:



    The reason why this is happening is because the horizontal hole (the square) ends at layer 124. That's why you will get a difference between those layers. Because at layer 125 both parts are not connected, so don't create a hole. 

    Hope you understand. Please let me know if you have more questions. 


    Here you have my project file with horizontal hole expansion on 0. AI3M_PartB.3mf

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    Posted (edited) · Inaccurate cura slicing

    "...would not introduce unwanted features/or rather features that are not designed onto the sliced model."


    The radius on the far side doesn't extend to the upright like the one on the near side does.  There is a jig-jog there.  The square "hole" starts at a different layer on one side than it does on the other side of the opening.  Above about layer 125 it is no longer a hole, but rather a gap between the two uprights.  The reason for that is the radius is not square to the model but rather runs at a slight angle (see the second image).  The feature indicated is symmetrical and appears on both ends of the model.  If this was a design intent, then it is very subtle and would require finer slicing.  I think Cura made an attempt to print this feature but at .12 layer height nad .4 nozzle, it was too fine to describe properly.


    The second image was with a .2 nozzle at .12 layer height.  You can see that there is a double line at the left bottom and the outer line is at an angle as Cura tries to make the feature because it is in the model.  The angle is 0.57755886°.






    This is the .2 gcode file opened in AutoCad.  The angle is apparent.  There is also a subtle angle in the counterbored pocket in the inside as witnessed by the non-parallel double lines.



    Edited by GregValiant
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    Posted · Inaccurate cura slicing

    Thank you both for the feedback.

    @GregValiant it was a design intent. I did set the slicing resolution to the smallest value possible and expected the sliced model to approximate as close as possible visually when printing with at 0.12 with a 0.4 nozzle but wasn't expecting the resolution error to contribute that much of an error. Although I'd imagine with the subtle feature removed, with horizontal hole expansion set to non-zero, the issue would still persist because at the change of the affected layer height, Cura no longer interprets it to be a hole and there would be a shift in the opening size.


    But thank you for the detailed analysis and time. I really appreciate the feedback. I'll be sure to keep all of this in mind for future designs/slicing.

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