Ferguson Mechanical Paradox for clock motion work

The mechanism animated here is the basis of a 12:1 gear reduction for clock hour and minute hand motion work. It relies on a fixed gear with 11 teeth (shown in blue) and a concentric gear with 12 teeth (shown in red) which drives the hour hand. The shaft that rotates the minute hand drives a carrier with a lantern pinion. There needs to be sufficient clearance between teeth to allow the pinion to rotate. The original mechanism was described by James Ferguson in 1764. For typical clock motion work the gear teeth are usually multiples of 11 and 12, typically 66 and 72 teeth which permits a more convenient pinion size.

Category:

Science & Technology

Tags:

• Clock
• Motion
• work
• horology
• mechanism
• Ferguson
• Paradox

[appropriatedesign]

With the fixed sun wheel attached to the front frame, the hour wheel and drive penetrating the sun wheel and frame to the hour hand and the minute hand drive running through all these from the back where the planetary pinion is driven through the carrier attached to the minute drive it should work without collision. My animation shows the planetary pinion arm at the front for clarity. This mechanism is used in some fine skeleton clocks and has appeared recently in model engineering exhibitions.

[TommyWylie]

This would be difficult to construct, because the blue wheel must remain fixed to the frame of the clock. I cannot see how the carrier would be able to rotate freely around the fixed wheel. It may be possible if the fixed wheel is next to the plate, and the carrier on the minute arbor is in front of it. The hour wheel would then be in front of this, but that would necessitate a double lantern pinion, as the carrier would have to be between the hour wheel and the fixed wheel.

[TommyWylie]

That is a true work of genius!