Introduction
For this week’s assignment, which goal was to create various impossible objects using two 3D printing methods, I decided to print a Crazy Cube and Low Voxel Bunny, both found projects of mathgrrl, an account thingiverse. The crazy cube, which employs the use of many printed hinges, peaked my interests because I loved the idea of having moving prints. In fact, all of the first objects I looked at had moving parts, starting with the fidget cube.
Failed print of fidget cube due to weakness of hinges.
This was originally going to be my printed piece but at the scale needed to fit in the gumball made the hinges too small to support rapid movements, a topic which will be discussed further. Additionally, two sets of objects were made due to limitations in one of the printing methods, which will also be discussed further.
Printing method 1: FDM
The first set of prints, using the FDM method, were done on the Prusa i3 mk3. After downloading the .stl file of the crazy cube, it was uploaded onto 3D printerOS, the slicing software used on the Prusa printer. From there, object was orientated onto the bed in the layout software and scaled down, with trial and error, to the dimensions to fit inside the gumball. A scale of 60% of the original size seemed to fit the gumball. When slicing the object, default settings of .2 mm layer height , 1 mm wall thickness, 215 degrees Celsius plate temperature, and skirt adhesion type were used. However, 25% infill density was used rather than the default 10% due to the desire to have sturdier prints.
Crazy Cube laying flat scaled at 80% vs 70%
Crazy Cube in cube form scaled at 80% vs 70%
I found that PLA was the best filament to use when it came to these prints. PETG, a flexible material which is used in one of the printers, seemed to make the object surprisingly rigid and made it so it couldn’t move as much. The set of the final three prints can be seen below.
Final prints all scaled to 60%
Printing method 2: SLA Printing
The 2nd set of prints, done using SLA printing, the Form 2 3D printers were used. For this printer, PreForm slicing software, made by formlabs, was used. For the software, I first opened the stl file and scaled it to my desired size. After that, I automatically orientated it and formed support structures using the magic wand feature in PreForm. The print is then queued and after it finishes, it is washed and cured in the machines to the left of the printers and the support material is removed to reveal the finished print.
Using the mentioned procedure, the first print I attempted was the same crazy cube I used in the FDM prints. However, after the print, I realized a limitation of SLA printing. When printing support materials, the supports are placed in gaps in the objects such as holes and things of that nature. For the hinges of the crazy cube, there are small gaps to allow for rotation. When the support material is printed onto the hinges, it restricts it’s movement and makes the entire object very rigid. This issue is can usually be fixed by removing the small supports near the hinge but for the scale needed to fit inside the gumball, it was not feasible. After consulting Dr. Wettergreen, I was told that I discovered a learning objective of the assignment and that I could keep the three FDM prints of the crazy cube and choose another object for the SLA prints. As such, I chose to print the pixelated bunnies which can be seen below. The first run through created a bunny too large for the gumball so it was scaled down to 65% of its original size.
Low Voxel Bunny scaled at 80% and 65%
Cost Analysis
Prusa FDM Costs:
- Raw Materials: The final print used up 17.58g of PLA material which 3DprinterOS says costs $0.35. With the trial and error in objects and scaling, the total material is upwards of 50g PLA and 10.2g PETG, making the total approximately 67.58g PLA and 10.2g PETG for this printing method. Assuming the same price conversion for the PETG print ($1/50.22g filament) , the total price of materials is $1.54
- Machine Cost: A total time of 11.4 hours printing.
- Labor Cost: As I was somewhat proficient in the use of the printers beforehand, lab assistant help was not needed, making the labor cost 0.
The total monetary cost of the FDM Prints is $1.54.
Form 2 SLA Costs;
- Raw Materials: The Grey Pro resin used in the final and test prints costs $175/L. The test and final prints ending up totaling 27.4 mL of resin used. Using the conversion of above, the price for the materials ends up being $4.79.
- Machine Cost: For a total of two preliminary prints and a final test print, the total machining time was 8.2 hours. Adding the .5 hours of curing and washing to the time for each print makes the total machining time to 9.7 hours.
- Labor Cost: As I was somewhat proficient in the use of the printers beforehand, lab assistant help was not needed, making the labor cost 0.
The total monetary cost of the SLA printer is $4.79, making the total cost of the assignment $6.33.
