“The fault, dear Brutus, lies not in our 3D Printers,
But in our post-processing, that we are underlings.”

–Cassius/OEDK, Julius Caesar, (I, ii, 140-141)

 

This week’s project was to 3D-print an object of our choice, on the condition that said object could not be created (easily) through any other means. I chose to focus on shapes with complex internal geometry, specifically nested shapes that would be nearly impossible to make without 3D-printing. I decided that I wanted to make a series of four nested spheres that could pivot on one another, forming a gyroscope. Using my trusty buddy IronCAD, I began to create a 3D-model that I could send to the printer. The first step to this process involved making a spherical shell, which I realized I could do using the rotation function. I hadn’t ever used the rotation function before, but I figured it couldn’t be too hard.

Haha jokes. The refrain from the CADventure appeared again, this time in a different guise, but the fix was surprisingly easy (and also reflecting a lapse in calculus knowledge, haha): in IronCAD, an object that spans both sides of the axis cannot be rotated across that axis. All I needed to do was rotate a semicircle rather than two concentric circles:

There were then no further complications using the rotational tool. In order to fit the space constraints of this project (the object must fit in a 2x2x2 inch cube), my largest sphere could only have a radius of 1 inch. I made each sphere .1 in. thick, with a gap size of .05 in. between each shell.

This may look like a sphere, but it’s actually a spherical shell, which became immediately apparent when I started cutting cylindrical holes into each axis.

In order to get the cylinders to intersect so that they were concentric with the x/y/z axes, I put the shell’s triball in its center and then aligned a cylindrical hole to be concentric with the triball. I then made three copies of the cylindrical shell in the exact same location, and rotated two of them 90 degrees in either plane. The end result turned out quite nicely. All I had to do next was make four spherical shells and add some pins and pivots for the spheres to spin on one another.

Single shell, shown above, with initial pins and pivots.

Close-up on nested pivots.

Close-up on nested spikes.

Figuring I was ready to print, I queued my newly-exported .stl file into the Dimension printer (with much Lab Tech assistance), loaded the print job, and left for the day. Success!

Alas. My pins, shown above were simply too tiny to nest inside of their pivots. Also (visible with squinting; center strut), one of the sides of the cubes had formed incorrectly, jutting outward rather than maintaining a spherical shape. Back to the drawing board. I needed to make the pins/pivots larger; on a higher resolution, the walls would not experience the aforementioned bowing.

Larger pins and pivots shown above. I went in to print again, and I was told to use the Objet printer, which apparently has crazy-high resolution and is generally a pretty rad thing. Once again, with copious Lab Tech assistance, I loaded and started the print job. When I came back the next day, it was actually pretty cool–my cube was encased in a block of support material (sorry, no photos D:) that needed to be removed. A Lab Tech offered to power wash the support material off of the cube, and I agreed.

The outer spherical shell, as well as two of the struts in the second-larger shell, snapped under the water pressure. Oops. I was told that this was because it wasn’t always kosher to use the power washer on Objet-printed shapes, but, just in case, I ended up thickening the struts of the spheres by shrinking the size of the cylindrical holes.

The final render, with helpfully-color-coded shells to distinguish each layer from the previous one. A lab tech and I loaded the revamped version back into the 3D-printer, and the result was actually quite lovely:

The shells actually spun quite nicely on one another with a little bit of post-processing filing, although I had issues reaching the innermost shell because of its size and its proximity/location of being buried beneath the other three shells. I decided to take a picture and then come back the next day to finish filing down the inner shell, and perhaps take a video.

Instead, I was greeted with this horrible sight. A chunk of two of the outer struts had broken off, and one of the second-largest struts had also snapped. I’m not really sure why, but there was no sign of the missing chunk from above, suggesting that part of sphere decided to run away?

Well. Iteration four. We were pros by now. The Objet was out of support material, and I also didn’t see the need to print three different iterations of a toy on such a high-quality printer, so I ended up using the Fordus instead. The initial product looked great!

I gingerly set about to post-processing with a tiny file, and began the detail-oriented task of snapping the pins into their respective pivots.

Also a success! The spherical shells do not rotate as easily on one another as they did in the much higher-quality Objet print, but it was more than enough to create some pretty mind-blowing orientations.

The final happy family!