Planning

This week, I will be 3D printing several “impossible” objects using a variety of 3D printing technologies. Impossible here means only that the objects would be infeasible to produce using other manufacturing methods.

I will be printing these “surprise eggs” from user agepbiz on Thingiverse. Once cracked open, they reveal a tiny jet with articulating wings.

The delicate internal features of the egg (particularly the hinge) would be very difficult to cast or create with conventional methods, but the internal gearing on the wings of the jet are, as far as I know, impossible to create without using additive methods like 3d printing.

Printing

The beauty of these designs is that they have no angles steeper than 45 degrees, and can thus be printed without supports. This came in very handy when fabricating as it reduced print times and simplified the process, especially with the SLA printers.

I first prototyped the eggs in several sizes and types of printing methods.

Unfortunately all the prints with SLA, though they look incredible with a glossy surface, fused the wings of the jets and the halves of the eggs. The process leaves resin in the spaces between the moving parts, so on the final cure, the parts all weld together. This is particularly evident in the egg, where one can barely see the mark where the slot between the halves should be.

I had to scale the eggs to 90% size to get them to fit in the gumballs. This caused a decrease in the precision of the print and therefore the functionality, but the models still worked, unlike the 80% tests. This downsizing caused me quite a bit of headache, as the gaps between the hinges and the wings of the jet sometimes fused, and caused the thin walls of the wing to occasionally fail. However, they succeeded ~75% of the time, which was enough to allow me to finish the project.

However, most of the prints succeeded on the FDM printers, and it was super cool to see the jets fold up and fit inside the eggs!

The final eggs and jets: All the eggs are FDM, but the left two jets are SLA (non-articulating).

 

PRicing

Eggs took 1:12 hours to print and 0.30$ worth of PLA, jets took 28 minutes to print and 0.05$ of PLA, including a bit of downtime between prints, this works out to ~2 hours per complete egg.

As 3D printing costs ~$1/hr , this means that each surprise egg cost about $2.35 in material and machine time. However, I need to multiply by 4/3 to account for the 75% loss from failed prints, for a total of ~$3.15

This could be reduced by modifying the tolerances in the file to avoid failed prints, and by printing more at a time on the same bed.

As there was limited human time put into printing them (I wasn’t in the building for most of the FDM prints), my time was minimal, possibly a few minutes per egg for setup and removing failed prints.