From motion to hands.
Exhibition 003 · Research & model limits · 27 September 2026
What the sources establish
Horopedia: Motion work explains the conventional connection from the center arbor through the cannon pinion to the minute hand, and the reduction that drives the hour hand. Its operation section also describes adjusting the hands through the setting train.
Horopedia: Cannon pinion describes the friction connection that carries running motion and allows setting slip. The minute wheel entry describes its wheel-and-pinion construction.
Horopedia: Fourth wheel supports the small-seconds arrangement used here. A central seconds display can use a different layout.
The teaching gear set
We chose 12 → 36 teeth for the first pair and 10 → 40 for the second. The hour hand is slowed by (36 ÷ 12) × (40 ÷ 10) = 12. Two external meshes reverse direction twice, so the main hands turn together.
The modules are 0.04 and 0.0384 in scene units. Both pitch-center distances equal 0.96, allowing the minute and hour hands to share the center. These counts and dimensions are our teaching geometry, not a named caliber.
What is simplified
- The upstream movement and detailed keyless setting mechanism are omitted. The small housing beside the stem represents that hidden setting drive.
- The crown’s interaction ratio is illustrative. The seconds continue while setting; this model has no stop-seconds mechanism.
- Tooth outlines, supports and material finishes are illustrative. Forces, clearances and friction are not physically simulated.
- The translucent dial reveals the wheels beneath it. Separation deliberately opens tooth contacts; only the assembled positions represent engagement.
- At 60× and 720× all hands keep their calculated ratios. Fast seconds may alias on a display; these modes are for observing minutes and hours.
- Close-ups run independent, labeled clocks using the same model geometry.
Verification
Automated checks cover hand periods, signed tooth ratios, common pitch-center distances, pause, setting independence and time wrapping. These checks verify the programmed model, not a production movement design.