In a world first, it's a big ball of springy springo wonder! This weighty print takes some post-processing finesse, but the result is something special.
Download includes the Springo Sphere Half, and an optional support model to reduce the amount of support material (Use the Support STL with supports disabled, or don't use the STL and enable standard supports, but make sure they aren't generated between the layers of the springo)
I got the best results printing with 3 outlines/shells, 0.15mm layer height, and enough solid top & bottom layers to make the spring part solid infill.
After carefully separating the coil with a thin palette knife, I trimmed off the bottom of the coil on each hemisphere and welded the parts together using a 3D pen [Scribbler V3] (I used ABS settings even though I printed in PLA to make a stronger connection). I used binder clips to hold the two halves together while doing the 3D pen work.
Maybe I'll put together a little instructional video since it does take some careful work. Please comment if you're interested!
Pictured model was printed with Melt.Ink Aqua Glow-in-the-Dark PLA filament