Blender (www.blender.org) is a fantastic program for a number of 3d tasks. Teaching blender from scratch is a big topic. Today, I’m just going to cover some topics specific to 3d printing, and show you some settings and tools to facilitate 3d printing.

Dimensions

Probably the first thing to set up is the dimensional “units”. The default dimensional units in blender are abstract, and do not correspond to any real world dimensions. Under “Scene Properties, you can set the Unit System to “Metric”, the Unit Scale to “0.001” for millimeters, and the Length display units to “Millimeters”.

View Port Clipping

When zooming in and out to inspect your model, it may disappear from your view. It is helpful to set the viewing clip space to the scale we’re working with. In the case of 3d printing, I find a “Clip Start” of 1mm, and a Clip “End” of 1000mm (1Meter) works well.

Shapes

If you’re coming from another graphics program like inkscape, yo may be surprised to find out that blender objects do not retain their shape association. When you add a circle, cube, etc. in blender, you can adjust the initial parameters such as radius and number of vertices, howevever, once you move on to the next operation, those vertices lose their association with the “shape” that we humans recognize. Instead, blender just treats them as a bunch of vertices. Therefore, you cannot just “resize” what you added as a circle to 20mm, or a cube to 20x30x10. Instead, you must “Select” vertices and manipulate the selected vertices through operations such as Grab, Scale, Rotate, etc.

Meshes

Only “Meshes” can be exported to an “.stl” file. You can create and work with any type of object you want, curve, nurbes, text, etc. But you will eventually have to Object > Convert to > Mesh from Curve/Meta/Surf/Text before exporting to your slicer.

Non-Manifold

When creating models for 3d printing, it is important to understand that objects in the real world must have volume. Three vertices can create what loosk like a triangle in 3d space, however, it is still a 2d object which has zero thickness, thus zero volume, and is therefore considered “non-manifold” is not printable. You have to “Extrude” the points to some “depth” or apply the “solidify” modifier in order to create an object with volume.

For instance, when creating a pencil holder, you might create a cube and delete the top “face”. You are then left with what looks like a paper thin sides and a bottom. In fact, paper has thickness, your model does not. Again, you have to draw and connect the “inside” walls, or extrude them, or use the solidify modifier to create walls with volume, and thus printable.

Furthermore, if there is just one missing face, such that water or air could get to both sides of some zero thickness wall, your model will be “non-manifold” and will not print.

Sanity Checks

When learning all this, I developed a pre-flight checklist of things to check before exporting the .stl file for the slicer. They were:

  1. Remove doubles: Edit mode, Select All, and Vertex > Merge Vertices by Distance (set “Merge Distance” in tool pallet to some reasonable non-zero number)
  2. Make sure there are no internal or hidden faces: Edit Mode, Select > Select by Trait > Interior Faces, Delete (x) > Faces Only
  3. Make sure all points are in one connected object: Edit Mode, Hover over a point and press Loop (l). This should highlight all points. Select > Invert (Ctrl-i) to see if any were unselected, Delete (x) > Vertices.
  4. All Face normals should point out from the surface: Edit Mode, Viewport Overlays > Normals > Face > Size, and then Mesh > Normals > Recalculate Outside (Shift-n).
  5. All surfaces should be faced, i.e. form a closed object: Edit Mode, Select > Select by Trait > Non-Manifold, should highlight nothing.

    Causes of Non-Manifold:
    • – https://www.sculpteo.com/en/3d-learning-hub/create-3d-file/fix-non-manifold-geometry/
    • Faces with Zero Volume (e.g. edge with a 3rd face, internal or external)
    • Faces connected at a single vertex (e.g. two cones connected at their points.)
    • Open objects (e.g. shape with zero thickness)
    • Interior Faces: Edit Mode, Select > Select by Trait > Interior Faces, Delete (x) > Faces Only
    • Normal pointing “In” instead of “Out”: Edit Mode, Viewport Overlays > Normals > Face > Size, and then Mesh > Normals > Recalculate Outside (Shift-n)
    • Disconnected Vertices and Edges: Edit Mode, Select > Select by Trait > Loose Geometry, Delete (x) > Verticies
    • Areas with no thickness (like 2 cones connected at their points)
    • Overlapping edges (one edge behind another)
  6. Scale should be set to 1.0, rotations and relocations should be applied: Object Mode, Object > Apply > All Transforms. If you have scaled, rotated, or moved an object in “Object Mode”, this will apply those transforms so that the slicer gets what you see.
  7. File > Save
  8. File > Export > .stl

Then I found the “3D-Print Toolbox” under Edit > Preferences > Add-ons, search for “3d”.

This add-on adds a new tab called “3D-Print” with some very helpful tools. The “Check All” will run a series of checks. You can click on the “Results” to highlight the errors it finds, such as “Intersect Face” or “Zero Edges”, etc.

Decoding the problem can still be a bit obscure, and after you think you’ve fixed an error, you do have to run the “Check All” again to see the new results. Still, this saves much time in looking for and identifying trouble spots.

  • Non-Manifold Edge: We’ve discussed “Non-Manifold” above.
    • Every “Face” has an inside and an outside. If the face is oriented the wrong way, it can raise this flag. I have found that Mesh > Normals > Recalculate Outside (Shift-n) sometimes fixes the problem.
    • There is a “Make Manifold” button that somties fixes other manifold errors, although somtimes it causes other errors that have to be fixed.
    • Other times, I have to go through and try to fix up the model by hand.
  • Bad Contig. Edges: These can happen when two faces with opposite “Normals” share an edge.

    It can often be fixed by Select All (A), and Mesh > Normals > Recalculate Outside (Shift-n).
  • Intersect Face: This is usually caused by two “connected” sets of vertices that overlap such that at least one face slices through another.

    The way to fix these is to separate the sets of verticies by some distance, or to delete the faces that intersect and create ne ones that do not slice through each other.
  • Zero Faces: These are faces with out much area. The “Degenerate” setting in the 3d-Print Toolbox pallet controls the threshold for this warning.

    Often you can simply apply Vertex > Merge Vertices by Distance, or select each group of vertices that create a zero face and apply Vertex > Merge Vertices > Collapse (or your desired method).
  • Zero Edges: These are very short edges. The “Degenerate” setting in the 3d-Print Toolbox pallet controls the threshold for this warning.

    Often you can simply apply Vertex > Merge Vertices by Distance, or select each group of vertices that create a zero edge and apply Vertex > Merge Vertices > Collapse (or your desired method).
  • Non-Flat Faces: These are ambiguous to render.

    Selecting those faces and applying Face > Triangulate Faces will often resolve the issues. If not, manual repair may be required.
  • Thin Faces: These are faces that may be thinner than can be printed. The “Thickness” setting in the 3d-Print Toolbox pallet controls the threshold for this warning.
  • Sharp Edge: This is a variation of “Thin Faces” for Thin Edges. An angle can be so shallow or sharp, that the thickness of the edge goes to zero and will not print correctly. The “Edge Sharp” setting in the 3d-Print Toolbox pallet controls the threshold for this warning.
  • Overhang Face: This is a face that may need support to be printed. 3d Printers can usually print up to about 45 degrees from vertical without support. The “Overhang” degree setting in the 3d-Print Toolbox pallet controls the threshold for this warning.

    If you click on “Overhang Face” in the Results section of the 3D-Print Toolbox pallet, and it only highlights the surfaces that are in contact with the build plate, then you’re done. If it highlights an overhang face higher in the model, then that face will require “support”, which can be configured in the slicer.

Export

Finally, once you’re happy with your model, the 3D-Print Toolbox has a convenient “Export” button to export a “.stl” file for your slicer. This button conveniently only exports the current object in “Edit” mode, or the highlighted objects in “Object” mode, so you don’t have to delete the camera, light or other object from your scene. That lets me keep versions and different parts of a larger project in the same blender file.

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