Product
5 copies of a Mobius spiral bangle, 3 printed on a Prusa i3 printer and 2 printed on a Prusa SL1S Speed printer.
Procedure
After some deliberation about what shapes were “impossible enough,” I settled on this file: “Mobius Bangle” by Creative_Hacker on Thingiverse.
Thingiverse file
I downloaded the .STL file, and imported it to cloud.3dprinteros.com. I went to Layout and made sure that it was on bed, centered, and optimally rotated.
Layout in 3DPrinterOS
Then I sliced it.
Slicing in 3DPrinterOS
I kept the default settings for layer height and infill density, and made sure that the “generate supports” box was checked and the adhesion type was “raft”. I used a raft because it makes it a lot easier to get the part off of the bed when the print is finished compared to a skirt or brim.
The printing took 2.5 hours, after which I got these three, all connected by the raft.
Prints from the Prusa i3, with supports still on
After this, I removed the supports. I was initially worried about getting the raft off of the parts, but it turned out to be pretty easy. They snapped right off.
Prusa i3 prints, supports removed
As for the resin printing, I started with the same .STL file. I opened it in PrusaSlicer, then rotated the pieces optimally – interestingly enough, optimal rotation usually means straight up and down or flat for FDM printers like the Prusa i3, but at an angle for SLA printers like resin printers. I then sent the file to the printer.
At first, the print took 20 minutes. While it is called a speed printer, this was suspiciously short. Turns out, I printed an extremely small object.
Tiny bangle
I decided to scale up the object by 350% to make it a bit more reasonably sized. The printing this time took about 40 minutes. After it had printed, I washed it. This was done by attaching the build plate onto a metal wash tray, then putting the wash tray into the curing machine. It ran on the wash cycle for 10 minutes, then I opened the lid and let it airdry for 5 more minutes.
Less tiny bangles, after washing
Then I put the two objects directly onto the base of the curing machine and let it cure for about an hour.
Here is the final result, before supports are removed:
Washed bangle, with supports
And here is the final final result:
Final resin print
Challenges
The main challenge for the FDM printing (the Prusa i3) was the resolution of the print, particularly on the bottom.
Bottom of the FDM printed bangle – you can see the individual lines of filament
Since it was printed on a flat bottom instead of being suspended in air like the resin prints, the details on the bottom were lost. Some resolution on the side was also lost.
Side view comparison – the FDM printed version on the left looks a bit pixellated compared to the resin print on the right
The main challenge I had for the resin printing was determining what size to make the prints. It was hard to determine how large the prints were going to turn out just looking at the slicing software. As a result, I made the first set of bangles laughably tiny. Better too small than too large, at least, since I didn’t waste all that much material.
Cost Analysis
Filament: $0.31 (based on estimate from 3DprinterOS)
Resin: $1.04 (based on 7ml of resin used and $149 for a 1L bottle of FormLabs resin)
Labor: 1 hour at $15/hr (includes finding and preparing file, setting up machines, and collecting completed objects from machine)
Total cost: $16.35
