Overview/Slicing for FDM

Coming into the 3d printing project, I was really excited to work with a technology I had a lot of experience with and try to challenge myself with something new.  I knew I wanted to experiment with print-in-place style designs, so when I heard we needed to print an “impossible object”, I felt like I had a good idea of what I wanted to do.  I settled on the classic print-in-place bearing that mesmerized me so much back when I first started 3d printing.  I knew the main challenge would be getting it to work at a scale suitable for the gumball capsules we were putting them in, so I went ahead and scaled the original file down to a 40mm diameter in PrusaSlicer while keeping all other dimensions the same.

Printing for FDM

I quickly printed this off on a Prusa MK3S and then used a 5mm hex wrench to break the “seal” on the bearing planets with a bit more torque.  After this, it spun very freely and everything felt great.  Based on this testing, I decided to just print three more of them with the exact same settings and followed the exact same process to get each of them working.  Pictured below is one of the gear bearings printing and the four complete FDM prints of the gear bearing!

Slicing/Printing for SLA

After finishing that, the next challenge was trying to successfully print a gear bearing in resin with an SLA printer.  My first attempt was me taking the same model as before and slicing it with no supports or pad.  The choice of no supports was because removed support burs could get in the way of rotation and no pad was so the gears weren’t bonded together by the pad.  I did this quickly in PrusaSlicer and printed it on the SL1S.  Below is a photo of it in the slicer and of the gear bearing on the bed before washing and curing.

After I removed the part and washed it, I tried the same technique I used before with a 5mm hex wrench to try and separate the pieces.  I chose to do this before curing so that some of the resin bonding it together was hopefully still soft.  However, I was unable to separate it before stripping the inside of the hex socket.  After closer inspection, I realized much of the bottom was completely bonded together and breaking it apart would be a hopeless effort.  I decided to cure the part as is because it looked great, so it did still make its way into a gumball capsule.  Here’s the final result:

I made one more attempt at resin printing the gear bearing later with supports but no pad; I still had no luck and ended up with a much less aesthetically pleasing result that I just ended up throwing out.  I still think there is room for improvement here and with enough settings tweaking/effort, one could get a successful resin print-in-place like this.  If I had time for it, I would continue making an effort at this, but time ended up constraining the effort and I decided to put the bearing that wouldn’t turn in the capsule regardless for its aesthetic value.  Here are all the gear bearings in their gumball capsules:

Reflection

If I were to do this project again, the only major change I would make would be in trying different ways to get a successful resin print.  I think everything I did for the FDM print was as good as it could get, except I might try to print each one in a different color so it matched the gumball capsule cap.  I had a really good time working with print-in-place designs and in the future will work more on learning to create my own print-in-place designs.

Cost Analysis

Labor: 2 hours at $15 an hour = $30

Filament: ~50g at $20 per kg = $1

Resin: I used a negligible amount in comparison to a bottle = $0

Printers, tools, and the gumball capsules are a shared resource = $0

Overall, it cost about $31 to complete this project, including labor and materials cost.