The Hourglass Stood Still... WITHOUT supports?!

YOU PRINTED THIS WITHOUT SUPPORTS?!

That's what your 3D-printing friends will say. You can, off course, print this model WITH supports. But they leave ugly marks on an otherwise smooth surface. Wouldn't it be nice to show off with your printing prowess?

This hourglass-sculpture consists of two heptagonal cones, slightly pivoted with respect to one another and linked together by helical supports. It is heavily influenced by Christopher Helmke's impossible shape, which can be found here: https://www.youtube.com/shorts/YKZoMUWuI8g. If this design finds you Christopher: Thanks for sharing your idea!

Now that you've seen that, you understand how this model can be made without any supports; the upper heptagonal cone is printed first, and embedded in the second part of the print. I printed both parts with a 0.4 mm nozzle, 0.12mm layer height and 25% adaptive cubic infill. All top layers will be treated with the ‘ironing’ technique. All-in-all, this makes for a very smooth-looking build. The upper heptagonal cone fits into the helical supports with 0.05 mm of (modelled) clearance around its perimeter. The model pictured was printed on a P1S with a textured PEI plate; I had no issues fitting the parts together.

It is important that you print the upper heptagonal cone (the cone without the helical supports) first!

Don't bother printing both objects on the same build plate. The bed adhesion is far too strong to tear off the singular cone mid-print (been there, tried that), and you might end up misaligning the other part (or: not being able to finish the print because you cannot remove the singular cone).

I built in a pause in the print profile of the part with the helical supports. At this point, you can drop the singular heptagonal cone upside-down into the support. Afterwards, the print may be resumed. Make sure to check that the bottom of the heptagonal cone and the top of the helical supports are flush! I did this with the ruler of my calipers.

This is a really great way to showcase the precision of the Bambu Lab printers. I'm still impressed that with merely 0.05 mm clearance on all sides, the parts slide together very easily; on a prototype with 0.1 mm of clearance, I could visibly wiggle the part around. 3D-printing has sure come a long way…

Happy printing, I hope you enjoy this little project :)