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Too Thick - Too Thin


scottmg
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Posted · Too Thick - Too Thin

Imagine printing a 'T' shape.  The skin for the current layer is printed along the middle of the T (|||||).  So as it's printing there's a short up and down path at the top of the T, and a long up and down path through the main part.  When printing the short path, constant back and forth, it's too thick.  When printing the long path, it's too thin. 

 

I assume this is what linear advance/flow compensation is for.  But I've experienced this to some extent with just about every printer and material I've owned.  The printers that support linear advance seem to have minor improvements, but going really slow is the only thing that seems to work all the time. 

 

So a couple of questions:

 

1) Does the Ultimaker 3 support any kind of linear advance/flow compensation?

2) Does Cura have any settings to fix this?

 

This seems like an imminently fixable problem.  Increase the flow for a long, fast straight away, slow the flow in high acceleration/high jerk areas. 

 

I took pictures, but they're terrible and dark.  If my description is unclear, I can do another print specifically to demonstrate the problem. 

 

 

Thanks for any input,

 

Scott

 

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    Posted · Too Thick - Too Thin

    So you mean that you get underextrusion on long lines of infill, and overextrusion on very short ones?

     

    I believe the overextrusion is caused by the nozzle having to slow down in order to take the 180° corner at each end of a line. But the extrusion rate keeps going, because pressure in the nozzle does not immediately drop to zero, so it momentarily overextrudes at corners. Those very short lines consist of nothing but corners. Printing a lot slower, and a bit cooler, should improve this but won't eliminate it. There may be other settings you could adjust, but I don't know them.

     

    I notice this effect too when it is printing the short infill-paths between the holes. Although it is hard to see here in the photo.

    warped1.thumb.jpg.c796132c0f7622f90d967d7645ae0c9c.jpg

     

    Here, this effect is slightly visible on the right edge of the right orange model. (The left- and center models are post-treated, the left with acetone-smoothing, the center with heat-treatment, so they don't count.)

    DSCN5950.thumb.JPG.c7d33bc4c5ffe03fb4f3a2e16c50288e.JPG

     

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    • 5 months later...
    Posted · Too Thick - Too Thin
    On 7/27/2020 at 9:23 AM, geert_2 said:

    So you mean that you get underextrusion on long lines of infill, and overextrusion on very short ones?

     

    I believe the overextrusion is caused by the nozzle having to slow down in order to take the 180° corner at each end of a line. But the extrusion rate keeps going, because pressure in the nozzle does not immediately drop to zero, so it momentarily overextrudes at corners. Those very short lines consist of nothing but corners. Printing a lot slower, and a bit cooler, should improve this but won't eliminate it. There may be other settings you could adjust, but I don't know them.

     

    I notice this effect too when it is printing the short infill-paths between the holes. Although it is hard to see here in the photo.

    warped1.thumb.jpg.c796132c0f7622f90d967d7645ae0c9c.jpg

     

    Here, this effect is slightly visible on the right edge of the right orange model. (The left- and center models are post-treated, the left with acetone-smoothing, the center with heat-treatment, so they don't count.)

    DSCN5950.thumb.JPG.c7d33bc4c5ffe03fb4f3a2e16c50288e.JPG

     

     

    Yes, you got it.  As I mentioned I believe linear advance in Marlin is intended to help, but I've never seen anything that leads me to believe the Ultimaker supports those codes. 

     

    I've tried turning up the acceleration and jerk settings so that it flies faster through turns, but the effect seems pretty marginal.

     

    It might make for larger files, but this seems like it could be something fixed in Cura as well.  I guess maybe it's time to look into creating a plugin myself. 

     

    Thanks for the info.

     

    Scott

     

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