Blender notes to self: 3D Printing

This post was written by eli on October 5, 2018
Posted Under: Blender and 3D

As I use Blender only occasionally, I’ve written down quite a few hints to myself for getting back to business. If this helps anyone else, so much better.

I’ve also written two similar posts on this matter: A general post on Blender and a post on rendering and animation.

Printing methods

See a summary chart on this page.

  • Fused deposition modeling (FDM/FFF): Melted plastic (ABS/PLA/Nylon) coming out from a nozzle. Layer thickness ~0.2mm. Cheap, but the geometry is limited to self-supported models, or the result literally drops. Also relatively limited accuracy and minimal thickness.
  • Selective laser sintering / melting(SLS/SLM/EBM): Laser sinters or melts a powdered material (typically nylon/polyamide). Layer thickness ~ 0.1mm. Good chemical properties (biocompatible) but the printer parts have surface porosity. EBM uses electrons instead of light.
  • Stereolithography (SLA/SL/DLP): Based upon curing of a photopolymer resin with a UV laser. Layer thickness ~ 0.05mm. High quality but expensive manufacturing.

Preparing for printing

  • The mesh must be manifold = no holes. Also, it should have no vertices, edges or faces that don’t enclose an volume, no intersection of bodies, no overlapping of edges or faces. Double vertices and edges are not good, but since the mesh is translated into STL, they go unnoticed as long as the duplicates are accurate. If they’re not, this causes warnings that can be ignored, but can lead to missing the important warnings.
  • Watch the model with Flat shading (click button in Tools) at the toolshelf to the left. Smooth shading is misleading.
  • When resizing in Object Mode, be sure to apply (Object > Apply > Scale), so that the measurements in Edit Mode (and otherwise) are correct. Same goes for applying rotation and possibly location.
  • The result is like at rendering. Bends done by bones are exported.
  • Export to .stl, which is a format consisting of just a list of triangles. The file doesn’t include units, which is why it’s required to state units when uploading a file.
  • In properties / Scene, set the Units to Metric and Scale to 0.001 for millimeters (these units will go to the STL file, which us unitless). It seems like this has more to do with interaction with Blender.
  • It seems like mm is the correct scale to use.
  • Also, in the “View” part of the properties pane (keystroke “n”), under Clip, make sure “End” is significantly larger than the objects involved, or there will be weird cut-out effects as the view is rotated and moved around. This property sets the “global cube”. What’s outside this cube becomes invisible — faces become partially cut.
  • In the same pane, under Mesh Display, consider enabling Length for “Edge Info”, which displays real-life measures of each edge. Only in Edit mode, only for selected edges
  • The 3D printing add-on should be enabled. At the left bar, there will be a 3D Printing tab, allowing for a volume calculation.
  • The recommended place to find a print shop is 3D Hubs (I have no affiliation with these guys).
  • Before uploading, do some cleanup: Mesh > Vertices > Remove Doubles, as well as the Cleanup/Isolated and Cleanup/Non-Manifold in the 3D printing toolbox.
  • If the 3D toolbox spins forever when pressing the “Volume” button, it’s not a good omen, obviously.
  • Once uploaded, odds are that a lot of warnings on non-manifold edges and intersected faces. These can be checked with Blender’s 3D Printing Toolbox. In particular note that in Edit Mode, there’s a button saying “Intersected Face” which selects the faces marked as intersected. The underlying reason is can be the use of the Boolean modifier, which may create a lot of double edges (two adjacent faces have separate edges instead of sharing one). These double edges occur a lot more than those causing warnings by these tools, probably only when there’s some difference between the two edges. If this is the reason for these warnings, there’s no problem going ahead printing (saying this from first-hand experience).
  • Pay attention to the “Infill” percentage, which means how much of the internal volumes contain with plastic vs. filled with air cubes by the printing software. The layer height also influences the precision and finish.
  • Matching parts: If one part is supposed to go into another, there is no need for an air gap, but there will be friction (my experience with a 2 mm blade into a groove with the exact width, ABS 200 um printing).

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