June 15, 2026
Description
A completely useless, completely satisfying desk fidget. Crank the
knob and the arm sweeps around, tracing a perfect ellipse over a groove
engraved in the base. It does nothing else. There is no point — *that is the
point.* A funny little mechanical toy, nothing more.
| STL | Qty | Role |
|--------------|-----|---------------------------------------------------|
| base.stl | 1 | square base, cross dovetail channels + ellipse groove |
| slider.stl| 2 | dovetail puck that shuttles in a channel; snap post on top |
| arm.stl | 1 | knobbed crank with two snap-fit bores |
Print the slider twice. All parts print flat, no supports.
Slide one slider into either dovetail channel from its open end.
2. Slide the second slider into the OTHER channel. **Both sliders must be
in DIFFERENT rails** — one left-right, one front-back. Don't fit the arm
before both sliders are seated or nothing lines up.
3. Press the arm straight down onto both slider posts — each clicks past a
snap ridge and is captive after that.
4. Crank the knob and watch it trace the ellipse. Forever. For no reason.
(See the exploded render for the layout.)
This is a toy, not a precision instrument. As the arm passes through the
crossroad where the two channels intersect, a slider occasionally fails to
track straight back into its tunnel and needs a tiny nudge — it can catch
on the lip of the crossing instead of gliding cleanly in. It still works and
it's still fun; just don't expect glass-smooth motion the whole way around. A
drop of dry PTFE/silicone lube on the channels helps.
Flat, no supports. 0.2 mm layers (0.12–0.16 mm for crisper channels), 3 walls,
15–20 % infill. The base is large and sticks fine — no brim needed. The full
parametric .scadis included; change the ellipse size, base size or fit
clearances and re-render.
License:
Creative Commons — Attribution
Miloslav Brožek
