Coil cup

thingiverse

This object was designed in OpenScad to push the limits of helical coil creation with an ellipse where the major axis curves around the center to form an arc matching the radius of the coil's circumference. By scaling identically along all three axes, any cross-section perpendicular to the tangent of the helical curve will reveal a circular profile, essentially a rod. Scale it up in your slicer to the desired size – unless you're aiming for a 2-liter container that actually holds nothing but air.