The Process

This week, I 3-D printed an impossible item. This means that it is basically impossible to create the object but I did it anyway because of the power of 3-D printing. I made a trefoil knot, which is a knot with one single rope that crosses itself three times. With traditional manufacturing methods, this would be very difficult to create as one continuous line for the knot, but with 3-D printing it is feasible.

I started by looking on thingiverse, and because this is a common item, it was not difficult to find an STL file. The one I found was by a user named kylekorn, and can be found at this URL:

https://www.thingiverse.com/thing:387146

I downloaded the STL file, and then opened it in the PrusaSlicer software on my personal laptop. I then used the largest layer height of 0.30mm and DRAFT quality because I wanted a quick print to ensure that the shape turned out how I wanted it to and that it would fit into the capsule. I took approximate measurements of the capsule to make my guess of 1.75″x1.64″x0.83″ for the print, and then sliced it and sent it to the printers.

The settings and gcode preview of the draft print (supports added after)

After printing, I removed the supports and tried fitting it into the capsule, and to my surprise it fit perfectly on the first try.

Initial draft print

I then created a new GCode with the same dimensions of the trefoil knot and then reduced the layer height to 0.20mm and the print style to QUALITY for a more detailed object, but that could still be printed in a reasonable amount of time. I printed 5 objects in case one I lost one of the prints or if they accidentally got ruined during removal of the supports.

Print settings and preview for final prints

The final FDM knots

These prints were all done on the Prusa FDM printers in the OEDK, but for my second form of print, I used the Formlabs SLA printer. I uploaded the original STL file to the Formlabs slicing software on the OEDK computer, and then scaled it down by 0.1 in order to achieve the same dimensions for the knot that I did for the FDM prints. I then used the One-Click Print feature to automatically generate the supports, and so I sent the file to the printer to get it started.

Slicing and starting the first SLA print

After the initial print was done, I placed it in the wash. After I removed it, I thought that it would be appropriate to remove the supports from the object, but with the tool that I was using and the fact that the resin was not completely cured, the tool made significant marks on the print and decreased the quality of it, making it rough to the touch.

First SLA print with supports removed early

I wanted the print to turn out smooth, and so I started another print with the exact same settings and this time I cured it before removing the supports, and it turned out much nicer.

Final Resin Piece

Because the piece was cured, when I removed the supports it was a much smoother finish, but it still had some bumps. To smooth these out, I used some 320 grit sandpaper. Once I was satisfied with the product, I placed the final SLA print along with the four FDM prints into their capsules, wrote the name and URL for the place that I obtained the file from, and I was complete!

Reflection:

This was one of the projects that I was more confident going into because I had used the 3-D printers before, however, only for FDM prints, not SLA. The process that I used for FDM was the same as I had used in previous prints, so this project further solidified the necessary steps for me, and allowed me to better gauge the difference in quality for the different sizes of layers and print quality settings in the Prusa software. For the SLA print, the most important thing I learned was to ensure that I complete post-processing steps in the appropriate order, so as not to affect the quality of the print negatively. Specifically, not to remove the supports or make any adjustments to the product before it is fully cured, so that the material is strong enough to resist any deformities caused by sharp tools or bending forces.

 

Cost Estimate:

59.616g PLA @ $0.029/g = $1.73

20g SLA Resin (estimate) @ $0.20/g = $4.00

6 hours Labor @ $15.00/hr = $90.00

Overhead Estimate (OEDK 3-D printers, utilities, etc.) = $25.00

Total Cost = $120.73