3D Printing an Impossible Object

Firstly, I used thingiverse to select an impossible object. Given that our final project is a chess set, I took this theme forwards and looked for ‘impossible’ pieces to print. The final piece I chose is not specifically from a chess set but it could be; it is an impossible object because it has a spiral staircase running through the centre of it which would make it difficult, if not impossible to manufacture using conventional methods.

FDM
I imported the file into Prusa Slicer to prepare the design. I used the default OEDK print settings for PLA, automatic generation for the supports, and used the scale function to create a miniature test piece. Unfortunately, when I returned to the OEDK  I could not find the print so it must have been misplaced, or was a failed print that someone got rid of. Without my test piece, I could not see whether the supports for the internal geometry had been successful. However with time constraints, I opted to go forward with the full-size print, scaled to 40mm in height for the provided gum ball capsules. 

I printed three castles out of standard, white PLA on the Prusa. I was pleased with how the pieces looked externally. However the supports for the internal staircase were large, and therefore very difficult to remove without damaging the more fragile elements of the gate and staircase. I first used small pliers, the  tweezers to remove these supports as best I could but some edges remained. I then used fine grit sandpaper to remove any sharp edges but there were one or two support elements that were unreachable.

Since the SLA printers were all in use, I made my next prints on the Bambu printers so I could try a new filament. I printed four further castle pieces out of red ABS. The first two prints got a little damaged as I attempted to remove the supports so I went back into the design software to adjust the supports. I made the supports thinner, increased their spacings the around the outside of the piece and reduced the number of supports on the internal staircase.

The second set of two was a more successful print. I removed the supports gently with tweezers, and use fine sandpaper to smooth any rough edges where the supports has been pulled away from the main piece. Whilst these two prints were not perfect, they were much better than the first two and the supports were easier to remove.

Then I was able to place all five prints into the gum ball capsules.

SLA
Aiming to complete SLA printing as well as FDM, I uploaded my test file to FormLabs to use with the resin printers.

Unfortunately this piece also disappeared :/

Since my first print had been misplaced or moved, I was fortunate enough to be able to jump in with Cassidy as she prepared her SLA prints, since there were no machines available at any other points in time. We loaded our designs into FormLabs – I oriented the part so that it would be built from the base up (auto orient wanted to place the part at an angle such that only one edge was connected to the base plate. This seemed flawed), and then used the auto settings provided by the software to create supports for the part.

This morning, I collected the part and placed it in the washer for a 15 minute wash cycle. Once I pulled it out, there were no signs of residual resin so I was to place it into the curing chamber which had been preheating. As recommended by FormLabs, I used a 60 minute cycle at 70 degrees. This completed the post-processing for this part.

Cleaned SLA plate with isopropyl alcohol, and tidied station after use:

Cost breakdown:

• Labour: 4hrs x $15/hr = $60
• Material:
  • PLA filament (1kg for $24.99 from Hatchbox3d.com – 2.5 cents per gram)
    • 1 missing test pieces: 6.04g * 2.5 = $0.15
    • Final pieces: 10.45g * 2.5 * 3 = $0.26*3
    • Total PLA cost: $0.93
  • Red ABS (1kg for $23.99 from Hatchbox3d.com – 2.4 cents per gram)
    • 2 test/failed pieces: 10.45g * 2.4 * 2 = $0.50
    • 2 complete pieces: $0.50
    • Total ABS filament cost: $1
  • Tough 1500 resin (Dynamism.com quotes $199.00 for 1l – $0.199/mL):
    • •  Test Piece (?):  ~8mL
      • 1 Final piece: (estimation since I did not calculate how much of the total usage was for Cassidy’s print vs mine): ~15mL
      • Total Resin Cost: $0.20/mL *23mL = $4.60
• Machine Costs: Free with OEDK access
• Total Cost: $66.53