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Shell thickness


pm_dude
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Posted · Shell thickness

Hello,

I've noticed that the shell thickness is done in a way that allow for compression a bit if you have a thickness of a little less than twice the nozzle size but wont allow it if you go above double the nozzle size.

I like to set the shell thickness to 0.7mm because it cause the inner and outer shell to overlap a bit and gives good adhesion depending on the material. I had cases where faster print would leave a gap between inner and outer shell and increased case of separation on some parts. I could have been printing at too low temp for the speed of print... Ninja flex is another case I like to overlap inner and outer shell.

So I was wondering if in the future versions of Cura there could be a way to specify the number of lines the shell should have and the overlap percentage (like the current infill). This way you could tell to print with 3 lines that have 15% overlap.

I want to start playing a bit more with shell thickness especially for translucent material that I would not want to have 100% infill but would want to have the same feeling.

 

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    Posted · Shell thickness

    They don't truly overlap - it's more complicated.

    I believe it will print from 75% to 150% of nozzle diameter so for .4mm nozzle that's .3mm to .6mm per pass. If you ask for a shell that is .7mm it does two .35mm passes. That means it positions the nozzle .35/2 mm (.175mm) inwards from the final finished edge and puts consecutive passes .35mm apart. Another way to think of this is that cura treats your nozzle as though it is a .35mm nozzle and extrudes only what a .35mm nozzle needs (underextrusion) and puts two passes .35 apart just like you would do with a .35mm nozzle. Even though in reality you have a .4mm nozzle.

    I can see how this would improve adhesion between the 2 shells but you might be better off just increasing the flow by 10% or so. Or fix the belts to remove any backlash or play. Or print slower or hotter because maybe you don't have backlash but instead have underextrusion (too much pressure in the nozzle - plastic can't get out fast enough).

    I always (almost always) set shell width to a multiple of nozzle diameter (e.g. .4, .8, 1.2, 1.6) as I get much better results that way (in my opinion). The only exception is for thin walls such as when I do text in which case I will often do .3mm shell. This comes out much better. I often simultaneously set the flow to 133%. But this is a special case.

     

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    Posted · Shell thickness

    I'm trying a print right now that uses 0 infill and 2mm shell. So far its doing great. I'll have to run the test again for this specific need cause this print is in wood fill and is set to flow at 130%. At least its the first time it doesnt clog at all :)

    I'm happy to see that you also boost the flow... I'm always having the impression its more a hack to counter real issues

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