Twisted, melted vase

A design called Twisted, melted vase by Neil Fusillo caught my eye on Thingiverse. I liked the translucent print, and it seemed like something big but not dense that I could print. It's not really melted and twisted, but it looks that way. The outside is ribbed, and a gentle swirl turns into an extreme distortion and then back again. My printer can go up to 200mm (7 7/8") high. It's provided as an STL file ready to print, so no opportunity to change it - probably created with MathCAD or some math-based design program. Even though it's not my design there are a number of decisions to make in order to print it successfully.

I have some translucent PET-G in green and magenta that should look nice and transmit light.

There was not a lot of detail about how to print it, so I did some half-scale samples. The provided file is a solid, i.e. the top is closed off, so I learned how to chop a couple millimeters off with Simplify3D. That makes it an open shell, but the thickness of the shell would be up to me. With three layers it was forecast to take 12 hours to print the full size, with 2 layers about 8 hours. So I did my test print at 2 layers.

My concern was that 2 layers might leave little gaps which would not be watertight. But 3 layers would not transmit quite as much light and make it less "glittery". I also wondered whether 2 layers would be strong enough in general. That turned out not to be a concern. This PET-G is slightly flexible but tough. With the glittery look you would think it would be brittle, but it's not at all.

Sure enough, the 2 layer print leaked like crazy. So I did a 3-layer half-high and tested again. This time it had just one little gap. I bought some acrylic to spray on the inside and hopefully make it much more solid. I divided the slicer settings so the bottom part is 3 layers and then it switches to 2 layers in the upper section. I printed one of these, sprayed 3 or 4 layers of acrylic, and then it was perfectly watertight. Maybe these little ones will become pencil holders.

This is the biggest thing I've ever printed. It took 13 hours and 14 minutes. It came out great, just one tiny blob flaw. I'll spray it with acrylic and then test whether it's waterproof.