Ticking Turn Timer — wind-up escapement, no electronics, no metal parts

Ticking Turn Timer — a printable mechanical escapement

Wind the knob one to two and a half turns, let go, and the bar on top starts rocking: tick — tick — tick, while the engraved arrow creeps back across the dial. When it stops, the turn is over. No battery, no electronics, no metal hardware — just seven printed parts and two coins.

⚠ PLEASE READ FIRST — this is a TOY / a demonstrator

It is not an accurate timer and it is not a useful clock. What it is: a working runaway pin-pallet escapement — the same family of mechanism that made mechanical clocks possible — shrunk to something an FDM printer can actually make, so you can hold it, wind it and watch the escapement do its job.

Set your expectations accordingly:

• The rate is not calibrated and drifts. Run time per wind depends on your filament, your tolerances, how heavy your coins are, even how warm the room is. Two people printing this will not get the same number of seconds.

• Expect a bench session. It is a v1. You will very likely need to tune it (heavier coins to slow it down, more wind if it stalls). The Tuning section in the bundled guide tells you exactly which number to change and which way.

• Use it as a "roughly this long" turn timer for a board game, or as a desk curiosity — not for anything where the actual number of seconds matters.

If you want a timer that measures time, buy a sand timer. If you want to understand — and hear — how an escapement works, print this.

How it works

• A flat spiral torsion spring in the floor stores the wind.

• It drives a 24-tooth escape wheel with sawtooth teeth.

• An anchor with two pins straddles 2.5 tooth pitches. Every tooth the wheel releases kicks the anchor sideways; half a pitch later the other pin catches the next tooth. Escape, lock, escape, lock — that alternation is the tick.

• The foliot — the bar across the top, with a coin in each end pocket — is the timekeeper. It has no spring; its inertia alone sets the rate, which is why it is a runaway escapement and why heavier coins slow it down.

• Every axis is vertical, so the whole thing simply lies flat on the table.

Parts — 7 printed, nothing else but two coins

Non-printed: 2 coins, Ø ≤ 20.5 mm and ≤ 2.5 mm thick — a 1 CZK, a 10 eurocent or a US cent all fit. Both pockets must carry the same coin, the bar has to stay balanced. Optionally two drops of super glue if the square drive tips end up loose. No screws, no bearings, no magnets.

Printing

Everything prints flat on the bed with no supports, no brim needed.

• 0.2 mm layers, 3 walls, 15 % infill — but 100 % for the spring, wheel and anchor (thin pins and a thin ribbon; they are wall-only anyway).

• The spring must be PETG. PLA creeps under sustained load and takes a permanent set — a PLA spring will go soft and stop pushing. Everything else is happy in PLA.

• wheel and anchor are exported underside-up so their pins point up and print narrow-end-up with no overhangs. You flip them over during assembly.

• Total ≈ 95 g at 100 % infill; expect 65–70 g with the settings above.

• Footprint Ø96 mm — fits any bed.

Assembly, step by step

Build bottom-up. Test as you go — once the cover snaps on, getting back in means prying the three snaps apart.

Step 1 — Prep the base. Set it down open side up. Find the three landmarks: the centre bore (wheel tip pin), the tall bored boss at one side (anchor pivot), and the C-shaped catch block with a vertical slit (spring tab). Clear any stringing out of the two bores.

Step 2 — Spring in. Drop it in flat and slide its straight outer tab down into the slit of the catch block. The hex hub should land centred over the floor bore. It sits loose on the floor — correct; it is held only by the tab.

Step 3 — Escape wheel in. Flip the wheel over so the hex arbor and the small tip pin point down. Feed the tip pin through the hole in the spring's hex hub and into the centre floor bore, then press until the hex fully engages. Check: spin the wheel — it should turn smoothly and wind the spring's inner coils, which should unwind again when you let go.

Step 4 — Anchor in. Flip the anchor over (pivot pin down) and drop that pin into the tall boss, pallet pins reaching toward the wheel. It will not drop in at just any wheel position — the pins only both clear the teeth over a narrow slice of rotation. Rest the anchor on the boss and turn the wheel slowly with your other finger until the anchor drops the last millimetre by itself. Never force it: if it needs pressure, the phase is wrong, not the fit. Check — this is the mechanism test. Rock the anchor left–right with a fingertip; each rock should release the wheel by half a tooth with an audible click. It should feel loose, never tight.

Step 5 — Cover on. Line its two bores up over the wheel hub (centre) and the anchor hub (offset), and the three snap bores over the three posts. Press straight down, evenly, until all three click.

Step 6 — Knob on. Press its square tip down through the centre bore into the wheel's square socket, until the disc is nearly touching the cover — it has to stay low so the foliot can sweep over it. Turning the knob should now turn the wheel.

Step 7 — Foliot on. Press its square tip through the offset bore into the anchor's socket. The bar ends up about 1 mm above the knob. Rocking the bar should rock the anchor and tick the wheel.

Step 8 — Coins in, run it. Press one coin into each pocket past the three little retention nubs, same weight both sides. Wind the knob until it feels firm — 2.5 turns maximum, that is the spring's stress limit — and let go.

Tuning — plan on doing this

• Ticks too fast / buzzy → heavier coins, or stack two per pocket.

• Stalls → lighter coins, or one more turn of wind.

• Wheel locks solid → the pallet pins dip too deep: increase pin_r in the source and reprint just the anchor (it is a 1 g, few-minute part).

• Wheel free-runs without catching → pins too shallow: decrease pin_r.

pin_r (default 30.3) is the pin-centre radius and the one number worth understanding: rocking the anchor moves one pin out and the other in by 0.224 mm per degree. Keep it inside 29.8–30.8. Below about 29.6 there is no wheel position where both pins clear at once and the anchor cannot be fitted at all — an earlier revision of this design had exactly that bug, which is why the source now ships with an automated check that seats the anchor against the wheel and reports the swing angle at which each pin catches a tooth.

Source

Designed from scratch in parametric OpenSCAD — no AI-generated geometry, no third-party libraries bundled. The attached escapement_timer_standalone.scad is self-contained and verified to export geometry byte-identical to the files above. Tooth count, wheel size, spring thickness, bar length and pin_r are all parameters at the top. Set part="base" … part="foliot" to export the pieces, or part="exploded" for the picture.