UMS5 Interesting dilemma with AA 0.25mm print core

[3DRocketry 1]

Ultimaker S5, Tough PLA Black 

 

Greetings, fellow 3D aficionados like myself and pros!

 

I have recently purchased AA 0.25mm print core by Ultimaker. I am trying to print as clean a gear as possible. I tired with 0.4mm core - using a profile by CHEP on YouTube. It came out very nice and clean. However, I was keen to see what kind of results I would be able to get with a smaller print core, since the gear I am trying to best is indeed quite small (17mm in diameter). 

I was surprised to see the following previews in Cura:

As one can see, bigger values for Layer Height produce more prominent "steps" (?) between layers. The smaller thew value for Layer height setting the smaller the steps. With Layer height value 0.06 and a rather think Line width seems to smooth out the steps. I find this occurrence very interesting. Would anyone please be so kind and share your thoughts and possible solutions for smoothing out the corners. Please find attached currently in use profile for UM S5.  

With Kind regards, 

V.A.

Fine#2.curaprofile

 

 

[GregValiant 1,251]

There are going to be steps on any slope or horizontal curve.  It's the nature of the beast.

The less the angle of the slope - the farther apart the steps are.  Cura works with a rectangular shape below the nozzle that is "Line Width x Layer Height" in size and so it has to move sideways for the next "jump" in the layer height.  The height of the step IS the Layer Height and you can think of it as the "resolution" in the Z.  The width of the step is a trig function of the Layer Height and the Line Width and the Slope Angle.

The Line Width is the resolution in the XY.  Line Width can be pushed about ±10% from the nozzle diameter.  The term "Line Width" is actually a misnomer as it is really the "Index Distance" between adjacent extrusions.  That's just semantics though.

You can try using "Adaptive Layers" but there will still be steps...they may be smaller depending on the settings.

 

A lot goes on in that little rectangle below the nozzle.  If you were to use PrusaSlicer then it isn't even a simple rectangle.

[3DRocketry 1]

Thank you so much! 

If you were to use PrusaSlicer then it isn't even a simple rectangle - what do you mean by that?

[GregValiant 1,251]

This is my understanding and it may be incomplete, over-simplified (or just plain wrong)...nevertheless I'll put it up here at least to start a discussion.

 

PrusaSlicer uses an oblong as the shape of the cross-section of a single extrusion, and Cura (and IdeaMaker and some others) use(s) a rectangle.  When two extrusions go down next to each other Cura is still a rectangle but the PrusaSlicer inverts the radius on the end of succeeding extrusions so they nest with the first extrusion (Image 1).  The difference is miniscule and gets lost because the printers aren't accurate enough to notice and we are dealing with molten plastic.  As far as I can see, there is no "better", just "different".  The math is slightly more complicated for PrusaSlicer, but that is in the background and nobody notices it.  When both programs are set up as close as I can get them, they both do a fine job, the prints look good, and are dimensionally accurate.

 

 

Back to steps...In the Image below the two yellow lines represent the outer surfaces of a model.  The rectangles are .2mm high x .4mm wide.

An 80° slope results in a step width of .04mm while a 5° slope results in a step width of 2.29mm and a slope of 1° would result in a step 11.46mm wide.  A lower slope results in the steps being farther apart as you see on the top of the cabin on a Benchy.  So with a slope angle of 90° the step width would be 0.00mm.  As the slope angle approaches 0° the width of the step approaches infinity.  Tangent(90° - slope angle°) * Layer Height = Step Width.  A layer height of 0.1 would result in steps that are 1/2 as wide as with a layer height of 0.2 and so Adaptive Layers is a useful tool to smooth the steps.  The lower the layer height the narrower the steps...BUT...There are always steps because your layer height will never be zero.

[3DRocketry 1]

This is great! Thank you very much for such a detailed explanation. Will definitely try Adaptive Layers.