Introduction

For our 3D Printing assignment, I decided to go with the Intermediate choice because I have some previous experience with 3D printing. My first impossible object of choice was a Math Gyro I downloaded from Thingiverse by Mathgrrl. The Math Gyro is considered an “impossible object” due to its interlocking parts printed through the Prusa’s layer by layer FDM printing approach. For the second printing approach, I went with Formlab’s SLA 3D printers which proved incompatible with the interlocking parts of the Math Gyro as the resin tended to stick together causing the pivots to lock. Thus, I went with the Rolling Knot from Mathgrrl on Thingiverse which is impossible because of its complicated geometry. The Prusa’s ability to print layer by layer with removable supports meant it was possible for it to replicate.

Prusa’s FDM Printers

Printing the Math Gyro on the Prusa’s FDM printers was simple as the file was already scaled to fit the gumball capsules.

 

The only thing left to do was to slice the file in 3DPrinterOs using its default settings for infill density (20%), wall thickness (1mm), layer height (0.2mm), printing temperature (215 Celcius), and Build Plate Adhesion Type (Skirt). No supports were required for this print which is important since the Prusa FDM printers didn’t have support material. Initially, I used the Prusa Printer with the flexible filament which ended up being a bad choice as the flexibility caused the gyro to come apart each and not spin very well.

Using the regular PLA filament, the prints came out nicely and spins smoothly as indicated in this video.

Prusa’s FDM Printing Cost

• Raw Materials: The print took up 0.14$ worth of filament per print according to 3DPrinterOs
• Labor Cost: Due to my experience as a Lab Assistant, Labor Cost was minimal and each print took only around 5 minutes to process
• Machine Time: Each print took 41 minutes to print.
• Toal Cost: 0.14$ x 3 = 0.42$
• Total Time: (5 minutes + 41 minutes) x 3= 138 minutes

Formlab SLA Printers

Initially, I tried to use the SLA printers to print the Math Gyros but I learned very quickly that wasn’t a good idea. I didn’t manage to get a picture of it, but the method of using liquid resin to form each layer meant it was prone to filling in the gaps between each ring of the Gyro. This led to the interlocking parts and rings of the gyro forming together preventing them from moving. As a result, I had to switch to a new object which ended up being the twisted knot.  This was perfect for the SLA printer as the twisted knot was a static object that needed supports which the Prusa FDM printers didn’t provide. The only hiccup was that the first print was too big for the capsule at 80% scaling so I scaled it down to 65% which fitted perfectly. Furthermore, a benefit of the SLA printing method is that printing multiple prints at once doesn’t drastically increase the print time. The downside is more time is taken up by the cleaning process to get rid of the excess resin and the curing process to give the material its full strength.

Formlab SLA Printing Cost

• Raw Materials: At 175$ per 1 Liter of Grey Pro Resin, 9.7 mL for both prints would cost (9.7mL*(175$/1000mL)=1.70$
• Labor Cost: 10 minutes to load the file and scale it + 5 minutes of removing the supports
• Machine Time: 2 hours and 15 minutes to print, 15 minutes for washing, and 30 minutes to cure two prints at the same time
• Total Cost: 1.46$
• Toal Time: 10 minutes +5 minutes +2 hours and 15 minutes + 15 minutes + 30 minutes = 3 hours and 15 minutes