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Why Thin Walls Fixes Lumps on Curves - In Crayon Explaination Needed


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Posted (edited) · Why Thin Walls Fixes Lumps on Curves - In Crayon Explaination Needed

I understand that thin walls helps deal with model sections that are smaller than the extrusion width; if I've got that right.

 

The sliced samples below are on Cura's 'Super Quality' setting with the max resolution upped to 0.5 and max deviation at 0.025. Thin wall are off.

Cura adds these slightly offset lines when slicing and they appear on the print in a uniform fashion. The black print is mirrored and the blebs appear mirrored on both sides. However thin walls enabled removes them, so great!

 

I'd just like to understand how or more so why Cura creates these judders at all. Is it the angle of the curve being less than the 0.4 nozzle setting can deal with so it just steps the wall in a bit? And if so, why doesn't that translate to the print and instead creates lumps not stepped in layers we see in the slice? Are the lumps result of sudden 90degree right then 90degree left direction changes?

This is more so a learning for me and hopefully anyone else who stumbles across it.

cura 1.png

cura 2.png

cura 3.jpg

Edited by Bumbletoon
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    Posted (edited) · Why Thin Walls Fixes Lumps on Curves - In Crayon Explaination Needed
    1 hour ago, Bumbletoon said:

    The sliced samples below are on Cura's 'Super Quality' setting with the max resolution upped to 0.5 and max deviation at 0.025. Thin wall are off.

    Max resolution upped to 0.5? Lower numbers are better. It's the minimum size something has to be to be included in the slice (otherwise it's just ignored), so lower number = higher detail. It exists mostly because of older printers that couldn't process all then gcode commands for fine details as fast as it should have been printing them, resulting in the print head "stalling" and blobs forming.

     

    1 hour ago, Bumbletoon said:

    I understand that thin walls helps deal with model sections that are smaller than the extrusion width; if I've got that right.

    Walls > Print Thin Walls will slice it so that walls in the model which are narrower than the minimum odd wall line width will be printed at the minimum odd wall line width instead of being ignored.

     

    The better setting to be looking at is Walls > Minimum Wall Line Width. This will let Cura narrow walls down to that size to most closely match the model (like the model might have something which is 2.5 regular line widths wide so instead of rounding up or down it'll print one wall at the minimum width and two at the normal width). The general guideline for line width is 60-150% of your nozzle size which for a 0.4mm nozzle (most common) is 0.24mm. And the minimum wall line width setting is used regardless of whether Print Thin Walls is on.

     

    1 hour ago, Bumbletoon said:

    I'd just like to understand how or more so why Cura creates these judders at all. Is it the angle of the curve being less than the 0.4 nozzle setting can deal with so it just steps the wall in a bit?

    Without having the Cura project file for it (if you want to share I'd be happy to try and give some more specific info) it's hard to tell just by the pictures. But a few things to bear in mind:

    • Curves are actually sliced as a lot of very short straight lines.
    • It's possible that it has to make an adjustment to stay within the maximum deviation, whereas it has more freedom in that regard the more it can vary the line width.
    • The size of the nozzle has pretty much nothing to do with the radius of curves you can pull off (which should be very tiny in any situation).
    • The preview in Cura isn't always 100% accurate as to the gcode commands being saved due to limitations in how it is rendered.
    1 hour ago, Bumbletoon said:

    Are the lumps result of sudden 90degree right then 90degree left direction changes?

    If you turn on Travels in the line type colour scheme, you should be able to see if that's what it does (it would be a very short blue line). You can also use the seeker bar at the bottom of the layer view to go back and forth to see each command as it does it. You can click it and then use the left/right arrow keys to seek by one move at a time.

     

    1 hour ago, Bumbletoon said:

    And if so, why doesn't that translate to the print and instead creates lumps not stepped in layers we see in the slice?

    If the lumps are caused by this (there's plenty of things that can cause them), it would be because the nozzle is staying in pretty much the same position for a little bit while still extruding, which means there's more filament deposited there than there should be, which results in lumps.

     

    Edit: forgot to mention another possibility - that could be how it is in the model and it's just following that when slicing. I've seen plenty of models with curves where you can make out distinct corners.

    Edited by Slashee_the_Cow
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    Posted · Why Thin Walls Fixes Lumps on Curves - In Crayon Explaination Needed

    Thank you very much for the reply! I'm new to Cura and 3D printing in general and suspect I got trolled on an answer on reddit re-resolution numbers. Ah well, I know now!

    The gcode preview has the layer judders in exactly the same place as where the blebs appear on the model however I understand what you mean by sometimes it may not be accurate.

     

    This is excellent advise end to end and I'm hoping to get some time this weekend to run some tests and put it into practice. Genuinely learnt a lot and gives me more to build on so thank you very much again!

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