For Homework 6, I knew I wanted an interlocking shape as my impossible object as I thought they would make a really nice keychain. I found Interlocking cubes by Jim2 on Thingiverse and decided to use it. He mentioned in the details that the cubes could be printed without support, which was one of the factors in me choosing it as it would save time in printing and energy in clipping the support out.

I used the Prusa FDM printer for my first three shapes. The first print failed due to the low contact area between the shape and the printing surface. I thought this was due to the contact point being a brim and not a raft, but changing it to raft didn’t help either.

Thinking that the problem was the Prusa machine itself, I switched to the Ultimaker. The printing head still knocked the shape off the surface, resulting in another failed print.

I finally added the option of support in addition to the raft to the shape, and it printed successfully on the Prusa. Snipping out the support with wire cutters was definitely a pain and left some unfortunate artifacts on the surface of the print. Overall, however, I was impressed with how quickly the print finished as well as the high quality.

For my last two shapes, I used the SLA printer Amicable Kitten on “Tough” setting. This print took a lot longer than the FDM printers (about 8 hours, where the Prusa took 3.5 hours), though the final product looked a lot smoother with no visible layers. After printing, it sat in an isopropyl alcohol bath for 20 minutes, and UV-cured for 20 minutes at 60 degrees F.

The support printed was a lot more delicate and harder to take out in one large piece. The plastic was also malleable on the surface, and left marks when I accidentally grazed it when snipping out the supports. The support contact area also left small artifacts.

Cost analysis (only for successful prints, not counting failed prints):

• Original Prusa I3 MK3S Kit – $749.00 (Prusa)
• Prusament PLA Vanilla White 1kg – $24.99 (Prusa)
  • Assuming each shape with supports was ~10g, 30g total = $0.75
• Form 3 Basic Package – $3,499.00 (Formlabs)
• Tough Resin 1 L – $175.00(Formlabs)
  • Assuming each shape with supports was ~20 mL, 60 mL total = $10.50
• Labor cost (assuming Texas minimum wage of $7.25/hr) – 3.5 hours (not counting print time as labor) = $25.38
• Total cost: $4284.63