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I'm relatively new to blender and trying to make this model.

enter image description here

The problem I'm facing is the slow incline towards the center seems smooth in this file but when I convert to an stl, these bumps appear in the layers.

enter image description here

enter image description here

I've tried recreating the faces in blender and adding edges to the incline but the bumps remain. Can anyone please tell me what I'm doing wrong and what I need to change in my model?

Thank you for your help!

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3 Answers 3

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STL exporter triangulates the mesh. If you want to see how the mesh will look like, when exported, triangulate it first.

Triangulate Modifier

Triangulate Faces operator (✲ CtrlT)

Each polygon in Blender is internally triangulated before it is displayed, however some attributes are calculated differently depending on when (where in the pipeline) this triangulation happens. For example, all triangles resulting from a single polygon will share face normal if the triangulation is implicit, but will have a separate normal calculated if the triangulation is explicit:

Above on the right is the default cube with the active vert raised up. The top quad no longer lies on one plane (because no such plane can be defined so that all 4 top vertices are on it), however the normal is calculated once and so the shading is flat across the entire poligon. On the left is the same cube exported to STL and imported back. The same could be achieved by simply triangulating the cube. Since the top polygon has been divided to two polygons, each has its normal calculated separately, normals differ, and so also shading differs.

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  • $\begingroup$ I see. So a curve in a face will cause this type of edge? $\endgroup$
    – BCove
    Commented Jan 4, 2023 at 16:00
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    $\begingroup$ @BCove ngons tend to triangulate in ugly ways. $\endgroup$ Commented Jan 4, 2023 at 17:39
  • $\begingroup$ @BCove more like faces that aren't flat. If a face isn't flat, it makes no difference to the Blender viewport (as you can see it's all the same colour anyway) but when you go to actually figure out where the face actually is, it's not so simple! Meanwhile, all triangles are flat by definition. $\endgroup$ Commented Jan 5, 2023 at 2:48
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One option would be to take a subdiv. approach to this model, ensuring a topology that flows around the geometry more evenly. When the triangulation is eventually made, it reflects the geometry more accurately.

One way would be to start in the flat, working with a Subdivision Surface modifier at the bottom of the stack all the way, so you can see what he resulting shape will be:

enter image description here

  • A plane, face-only deleted, CtrlShiftB vertex-bevelled at the corners and then subdivided nice and evenly along the sides
  • CtrlF > Grid-Filled, 1/4 cut out, and given a Mirror in X and Y
  • The cluster of 4 quads in the corner F merged and then CtrlF > poked to put an 8-pole vertex star in the middle of the face, and that vertex CtrlShiftB bevelled to make a ring
  • The shipped add-on Loop Tools > Circle can be used to make the ring circular. the circle can be rotated to an acceptable alignment. The surrounding vertices can be GG eased into an accommodating shape. The circle can be I inset at this stage, to isolate it. The vertices around the central point can also be eased outward,preparing for:

enter image description here

  • The Mirror being applied, all merged, and the central hole being made in the same way as the ones in the corners. The circular hole-faces are deleted.
  • Now the whole lot can be E extruded.
  • With one top-face selected, ShiftG > Select Co-Planar, and CtrlG create a vertex-group from the top surface. Create a Lattice object to enclose the model. Give the model a Lattice Modifier using the lattice, and aimed at the vertex-group, to create the curvature in the top face. Edit the lattice in Z only.

A hand-bevel / sliding loops in Z only, can give you the countersinks on the corner holes.

The whole object can then be given a Bevel modifier by angle, 2 segments, Shape 1 to put holding loops on the sharp edges.

This is just one way.. there will be others, but the point is to achieve even, flowing topology across the surface:

enter image description here

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Part of the issue is that any layer-based 3D printing will have a certain amount of terrace-like texture simply because of the layers. You can reduce this by lowering your layer height, but this may significantly increase printing time.

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  • $\begingroup$ Whoops! Looking at the OP now, this might be the correct answer… 🤔 $\endgroup$ Commented Jan 5, 2023 at 9:31
  • $\begingroup$ I think OP is talking about the artifacts in the second image from top, not the (perfectly expected) terrace in the 3D print. $\endgroup$
    – pipe
    Commented Jan 5, 2023 at 12:50
  • $\begingroup$ Non-planar slicing solves the issue. $\endgroup$
    – Leo Aguiar
    Commented Jan 6, 2023 at 2:58

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