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I have a model of an eye that I custom made in Blender 2.83 that when printed only creates roughness on the printed object near where I had the supports. The supports are not the cause of the roughness (at least not completely) since the supports don't even touch the parts of the print where the majority of the roughness and bumps are (refer to my photos of the print)

The roughness is only near the bottom part of the sphere as it prints upwards (refer to photos)

What I'm looking for is a technique or any suggestions for printing this without the roughness so it's smooth like in the rest of the print. I'm also curious what is causing the roughness.

Eye Model in Blender

Eye model in blender

Blender Scale Ratio: 0.001

Blender Units: mm

Eye Model in Prusa Slicer

Layer Gif

Eye Model in Prusa Slicer

Prusa Slicer Main Settings (Higher Res)

Prusa Slicer Main Settings (Higher Res)

Variable Layer Heights For Smoothness

Variable Layer Heights For Smoothness

Eye Model Prints Photos

Eye Model Small Version 3D Print (Notice it's smooth on top of print)

Eye Model Small Version 3D Print

Eye Model Small Version 3D Print Trouble Area

Eye Model Small Version 3D Print Trouble Area

Eye Model Small & Large Version With Support (Notice roughness on the sphere)

Eye Model Small & Large Version With Support

Example of Support Used On Small Print

Example of Support Used On Small Print

Smooth on inside of print

Smooth on Inside

--------- Print Details ---------

Printer: Prusa i3 MK3s

Filament: PLA Galaxy Silver (Prusa Reserach)

Slicer Software: Prusa Slicer

Print Temperature First Layer: 205 degrees

Print Temperature Other Layers: 190 degrees

Notes: The suggested temperature for the filament is 205-215, I've adjusted after careful calibration given my environment to a lower temperature to reduce stringing. I created a tower at different temperatures and discovered 190 was the perfect setting to reduce stringing in my case with this material. Refer to my screenshot below. I do not think temperature has anything to do with this since the print is smooth inside and near the top without any issues.

Temperature Tower Test For Filament Photo:

(Note stringing in the cone test areas at 225 to 205)

Temperature Tower

--------- Prusa Slicer Settings Photos ---------

Filament settings

filament settings

Extruder Settings

extruder settings

Support Settings

Support Settings

Joseph Astrahan
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3 Answers3

5

While Trish is completely right that the roughness can't be completely eliminated (you can't print a perfect spherical surface with discrete layers), the situation can be improved dramatically. The most telling photo in your question is the one of the removed support structure.

The part of your sphere that's seriously rough is all severe overhang. In this region, the outer wall of layer N+1 barely overlaps the outer wall of layer N, if at all, and without support would be printed mostly or entirely over thin air, failing to attach to anything and sagging/curling down randomly according to tensions in the extruded material, air currents, etc.

Now, with support material that's not entirely the case. Every so often (looks like a 2 mm grid) there are support lines under the overhanging outer wall. These will anchor it every so often and keep it from curling or sagging too much, but they don't actually constrain it to the place the slicer wanted the wall to go, and they don't provide a surface for the extruded material to press against to get the desired (e.g. 0.4 mm wide by 0.1 mm thick) extrusion cross section; instead the cross section will tend to be circular as a result of tensions within the molten material.

In order to get a decent surface over support material, you need what slicers call "Support Interface" or "Support Roof" (these are the names Cura uses; I suspect it's similar in Prusa Slicer). This feature builds a top surface as part of the support material itself for the supported part of the model to rest upon and press against. Of course that can make support harder (potentially a lot harder) to remove, and depends on tuning the Z distance between the model and the support as a tradeoff between quality and difficulty of removal, but it should get you much better results.

R.. GitHub STOP HELPING ICE
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  • I was doing some research and there is water soluble supports that prusa creates. Do you think this would work well if I used these supports eveywhere? It's located here https://shop.prusa3d.com/en/special/169-primaselect-pva-soluble-support-500g.html (what you are saying would work well possibly with this) – Joseph Astrahan Jun 21 '20 at 23:30
  • Yes, with dual extruder and soluble supports you can use a zero gap between support and model, and get much better results. – R.. GitHub STOP HELPING ICE Jun 22 '20 at 01:32
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    From my experience, supported material will often not look significantly better than what has already been achieved. Better cooling may help, but printing the sphere in two pieces would be optimal. – towe Jun 22 '20 at 09:57
  • He also needs to improve cooling. If the material cools down quicker there is also fewer artefacts – Onno Jun 24 '20 at 14:20
  • The roofs help a lot, I used them in other cases and the results are quite nice. – FarO Mar 16 '21 at 11:02
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You can't print them smooth

The short answer is: with FDM you can't make curves that go into the Z-direction. The better question is: Why?

Let's look at why it is rough: the roughness is from the layer height and the thickness of the perimeters (walls). At some point, perimeters of the given thickness have to be placed in a way that does not cover up fully anymore. Let's look at this example of stacking. At first, how looks a sphere close to the equator? well, the stacking is rather easy there. Think of each printed wall as a rectangular crossection and you get this pattern:

enter image description here

As we move further up along the print, the overlap between each subsequent layer gets less and less. Somewhere in the middle we are at this situation:

enter image description here

Till at the top of the dome this happens: The steps appear coarser and coarser and in the end create a very visible and feelable stepping pattern. Also, the top layer might get skipped because it is not a full layer height, depending on the slicer settings..

enter image description here

Mitigating?

But there are ways to mitigate the sphere problem to some degree.

  • reduce layer height a lot on the areas that are curved such heavily, though this has a direct effect on print time and can impact the quality.
  • Don't use an FDM printer but an SLS printer with layer heights that are fractions of the layer heights possible with FDM
  • Cut up your sphere. An example cut up is here, but there are other options. If your print orientation is not mandatory, you can even cut your sphere up and reorient it to achieve this, mitigating both the layer problem as well as making support use 0:

enter image description here

Post-Processing

The only true way to get rid of the layer lines is post processing. In this case I strongly suggest to use a filler and then sand off the excess material.

Trish
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  • I commented this on the other answer as well, but do you think adding supports everywhere with something like this (https://shop.prusa3d.com/en/special/169-primaselect-pva-soluble-support-500g.html) would help? it's a water soluble solution for the supports. I actually have ordered the upgrade kit for multiple filaments already for my printer so this might work. What do you think? (Thank you again for your answer, it was very detailed and helped me understand the issue). – Joseph Astrahan Jun 21 '20 at 23:35
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    different question, but yes, if you'd have a dual extruder or the MMU, you could. – Trish Jun 22 '20 at 08:47
  • "Also, the top layer gets skipped because it is not a full layer height." <- this is slicing-choice dependent. For example Cura in the default mode slices using the cross-section at the middle of the layer, which would yield a top layer that doens't get skipped. Cura in "exclusive" slicing tolerance mode intersects the top and bottom cross-section of each layer and would give an empty layer, like you say. – R.. GitHub STOP HELPING ICE Apr 11 '22 at 12:46
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I’ve noticed the best way to get it smooth without support is to make the printer print the inner parts of the model first. That way it gives the hanging layer something to hold on to. I turn my window ac unit up to high aim it at the printer so it cools the filament quickly. Next you’re going to want to mess around with the extruder heat. Try to get it as low as possible but watch out for the good gooey bad gooey range. If the first overhanging layer is close to the bed turn the bed heat off. Then tinker with the flow try to get it low but not super low I go as low as 70 enter image description here

Marcus
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