Twisted Ribbed Pen Cup — one part, no supports

Twisted Ribbed Pen Cup

A rounded-square desk cup whose entire surface is fine ribs turning through 90 degrees from the base to the rim. It catches light the way a fluted glass does: the highlight runs diagonally across the ribs and moves as you walk past it.

50 x 50 x 70 mm (63 mm across the twisted corners) · about 40 g · one part · no supports · no glue · no hardware.

The wall is the same thickness everywhere

The inside is not a plain cylinder with a decorated outside. The cavity is twisted at exactly the same rate as the shell, so the wall stays 1.6 mm measured at the bottom of a rib valley at every height — it does not thin out where the twist is steepest, and there is no pocket inside for dust or water to sit in.

Two other things fall out of how it is cut:

- The ribs are spaced by arc length , not by angle, so a rib on the rounded corner has the same 3 mm pitch as a rib on the flat. Nothing bunches up at the corners.

- The rib count is rounded to a whole number around the perimeter, so the pattern closes on itself — there is no seam where the last rib meets the first.

The bottom 9 mm is a plain untwisted band with a 0.5 mm chamfer at the bed edge, which gives it a clean foot, a flat first layer and somewhere to grip.

Printing

0.2 mm layers, 3-4 walls, 2 mm floor, 10-15 % infill. No supports — the twist never produces a real overhang (measured: 15 mm² of down-faces past 45°, all of it at the band seam). The ribs run with the twist, so layer lines fall into the valleys and the print reads as texture rather than as layers.

It also prints well in vase mode if your slicer will spiralize it — the model is one continuous shell around a single cavity.

A silk or metallic filament is worth using here. The ribs are what make it, and a filament with some sheen puts a moving highlight on every one of them.

What it holds

Pens and pencils, obviously, but at 63 mm across and 70 mm tall it is also the right size for makeup brushes, a toothbrush and paste, kitchen utensils, or cotton buds. It has no drainage, so it is a dry cup — do not stand a wet toothbrush in it and expect it to dry.

Parametric

The OpenSCAD source ships with the model, and everything worth changing is a named variable in the first twenty lines:

twist 90 degrees of turn over the ribbed section rib_pitch 3.0 crest-to-crest along the outline, mm rib_depth 0.9 crest-to-valley, mm rib_sharp 0.55 <1 = round crests, narrow valleys side 50 outer width at the crests, mm height 70 total height, mm corner_r 9 plan-view corner radius, mm base_h 9 plain untwisted band at the bottom, mm wall 1.6 wall thickness at a rib valley, mm

corner_r = 0 gives a sharp-cornered square, corner_r = side/2 gives a round cup, and twist between 45 and 180 changes the character completely. Raise height for a utensil crock, drop it for a business-card cup.