Smooth Circles

Discussion in 'Design and Modeling' started by angelenterprise, Apr 20, 2013.

  1. angelenterprise
    angelenterprise New Member
    I am drawing in Sketchup and converting the files to stl in Meshlab. When I upload the design to Shapeways the circles look choppy (the 24 sided polygon that sketchup creates). How is the best way to smooth those? Or do they automatically print smooth. Smoothing edges in Sketchup or Meshlab doesnt seem to change the uploaded drawing.

    Thank you.
  2. stonysmith
    stonysmith Well-Known Member Moderator
    You must select the number of faces BEFORE you draw the circle.
    When you first select the circle tool, the Measurement Toolbar shows the number of faces that will be drawn.
    You have to over-type this number and press ENTER before you start the circle.

    The number should stay as the default for the rest of your editing session, but it'll go back to 24 the next time you start Sketchup.
    Unfortunately, for any circles you've already drawn, I don't think you can change them afterwards.

    Meshlab and other tools have options for "Subdivision Surfaces", but those often make a bigger mess than they correct.
    JACANT Well-Known Member
    To see the effect, pick 'View - Hidden Geometry'
  4. angelenterprise
    angelenterprise New Member
    Thank you. That makes sense. How many sides would you typically make the circle to make it print fairly smooth? 50 or 100?

    Thank you again for the response.
  5. denali3ddesign
    denali3ddesign New Member
    Depends on the diameter of your circle...larger circles need more segments. Try to get the length of each segment 0.5mm - 1mm in length.
  6. stonysmith
    stonysmith Well-Known Member Moderator
    The number of facets required to be "smooth" changes based upon how large the object is.
    There is no single "magic" number of facets that will work in all sizes.

    If you are designing a 1mm diameter object, then even 16 sides will appear round-ish.
    But if you're designing a 50mm circle, you will need to be up in the thousands.

    Math Alert:
    The technical answer is: pick the material you want to print in, then look at the design rules page.
    You will find there a number for "Minimum Detail" size.
    The smoothest possible face dimension will be one half of that size.

    Example: WSF has a minimum detail of 0.2mm
    Therefore you need faces of at most 0.1mm width.

    For a 10mm circle, the circumference is 62.8mm so you need ~650 sides.

    Note: as your objects get larger, this presents a bit of a problem because each "face" has to be a triangle, and Shapeways has a one million triangle limit per model. That means reducing the number of faces and/or getting crafty with how the model is designed.
    Last edited: Apr 21, 2013