This week’s assignment is to design and create impossible objects using two different 3D printing methods (FDM and SLA).
I first looked on Thingiverse for some inspiration, but I didn’t really like many of them. A lot of them seem like weird-looking knots (example below) to me while others seem extremely difficult to print, often needing support.
(source: makerhome.blogspot.com/2014/01/day-150-trefoil-torus-knots.html)
Because I am lazy and didn’t want to deal with removing the supports and sanding the piece down, I am looking to design something that does not need support to print well. I also wanted something that is geometrically complex so that it is “impossible”, but does not take a lot of time to design. My solution to that was tessellation. With tessellation, I only have to design one section and just copy it over and over again in a pattern. The first thing that came to mind when I thought of tessellation was hexagons. That, combined with the inspiration from the bone cross-section I saw in class, is how I basically came up with the design.
(source: www.pinterest.com/pin/75998312435698422/)
3D-printed bone crossection
I printed my first two prints overnight and it took 9h40m each (the green and blue one in the picture below). This first print was to see what it looked like and see how big it actually was. In the morning I came to the OEDK to collect my prints and I was pleasantly surprised with the design. Unfortunately, it was too big and did not fit in the plastic container. I scaled it down to what I think would fit (x&y-85%, z-70%) and printed it again, this time I tried to slice it so that it would print as fast a possible to see if the size was good (0.4mm layer height, 0.5mm wall thickness, 15% infill). This print took 1h27m, and it was the perfect size for the plastic container (the white one in the picture).
Initial prints
I then proceeded to print the four better quality prints (0.2mm layer height, 1mm wall thickness, 20% infill) using two different printers, because 2 were available at the time. That meant I would print two on each printer. Note: All the prints until this point was done using FDM printers (Prusa mini and Prusa I3 MK3) and PLA.
At the same time, I took the STL file to another computer to slice it using the Prusa slicer so that it could be printed using SLA on the Prusa SL1S. After slicing, I printed it using the SL1S printer and washed it in the CW1S. The print took 31m35s and 31.68ml of the liquid, and the washing took 10 minutes.
Here are the final results: hexagonal prisms made from tessellated hexagonal towers which change in size as you move up and down the tower. 7 out of 9 are made from PLA using FDM, and 2 are made from UV-curing resin using SLA. The awesome thing is, these objects can be tesselated as well!
A little note on failures/imperfections…
Luckily there were no complete failed prints for this assignment, but there were some imperfections in the prints. There was one imperfection in the FDM and one or two bubbles in one of the SLA prints which are amazing. I think the reason there are no major failures is that the design itself lending well to 3d-printing, having minimal overhang angles.
A little note on costs and time…
The cost of the PLA used for FDM prints is calculated by 3DPrinterOS using the weight of the print, and the cost of resin used for SLA prints is calculated based on the weight. The total weight of the prints using PLA was 144 grams giving a cost of $2.97. The two objects printed using SLA weighed 35g combined. One bottle of 1kg Prusa tough orange resin used costs $69, making the cost of material for this equal $2.42. The summary of material costs and printing time is shown in the table below. The total labor required is approximately 2 hours, and at $10/hr, that equates to $20 of labor cost. Total costs excluding printer usage is approximately $25.39, with the majority being labor.
You can find the SLA file at thingiverse.com/thing:4975361
