Valence shell electron pair repulsion (VSEPR) theory teaching model kit

I wanted to add prints showing the valence shell electron pair repulsion (VSEPR) theory for the most common geometries to my undergraduate general and inorganic chemistry course. My intention was that this would help students understand the geometry of molecules and how to draw molecules on paper, in addition to the explanations on slides.

I use the large model for a lecture hall with a maximum of 300 seats, and the small model (60% scale) for seminar rooms or classrooms with much fewer seats. The individual parts of the models (spheres, bonds and lone pairs) are held together by magnets and washers, so that it is possible to assemble and disassemble the models on the fly during the lecture, e.g. to change substituents with lone pairs. The magnets and washers are attached with M4 screws, for which heat-set inserts are added to the parts. In my case, I placed the magnets in the pockets of the spheres and the washers on the bonds and lone pairs (printed as separate parts and glued together).

I had problems with the washers because the screws were sticking out, so a proper flat connection with the magnets was not possible. The solution was to glue M8 washers on top of the M4 washers with instant glue (rated for metal) so that the screw head was properly buried in the resulting pocket. 

Theoretically, any geometry (up to those with 6 electron pairs / a "steric number" of 6) can be shown by printing only the following parts:

• 3 central atoms:
  • tetrahedral
  • trigonal bipyramidal
  • octahedral
• 6 bonds
• 6 substituents
• 3 free electron pairs

Commercial parts for the large models:

• 20 x 7 mm magnets with a hole for M4 screws
• 20 mm M4 washer
• 25 mm M8 washer
• M4 x 8.1 heat-set inserts

Commercial parts for the small models:

• 15 x 3 mm magnets with a hole for M4 screws
• 15 mm M4 washer
• 15 mm M8 washer
• M4 x 4.0 heat-set inserts

Our print settings were:

• material: PLA
• nozzle diameter: 0.8 mm
• layer height: 0.2 mm
• line width: 0.8 mm
• wall thickness: 2.4 mm
• top/bottom thickness: 2.4 mm
• infill: 10 % gyroid (for large models) / 15 % gyroid (for small models)
• printing temp.: 210 °C
• fan speed: 100 %
• build plate: glass + Magigoo Original
• build plate temp.: 60 °C
• Print speed:
  • infill = 45 mm/s
  • outer wall = 35 mm/s
  • inner wall = 40 mm/s
  • top/bottom = 35 mm/s
  • support = 25 mm/s
• I used water soluble PVA as a support for easy removal
• supports are not necessary for bonds (printed upright) and lone pairs (printed as two parts)
• brim: 5 mm (for spheres) / 7 mm (for lone pairs) / 20 mm (for upright bonds)