The entire mechanism, except for a two-pound weight and a length of cotton string to support it, is made out of unmodified LEGO parts. The clock face mechanism is the same as that designed by Leo Dorst, but with the four mechanisms geared in lock-step at their minute hand axles. The pendulum is approximately three feet long, and hangs down the tower shaft and through a cutout in the table beneath the building. The two-pound weight is also suspended down the tower shaft and allowed to slowly drop all the way to the floor.

The entire clock mechanism resides in the top portion of the tower shaft, and can be taken apart in functional layers for easier maintainance. The head of the tower contains the gearing to run four clock faces off of a single minute-hand input axle. When this top portion of the tower is removed from the model, any one of the minute hands can be rotated to set the correct time of all four faces before re-assembly. Immediately below this is the pulley (a wheel hub) from which the weight is suspended. A gear train in the tower shaft leads down to the escapement mechanism and the pivot point for the pendulum. The pendulum is constructed of a series of 12-stud axles with a 4-oz. LEGO weight element connected at the bottom. The clock works perfectly well without the weight on the pendulum, but the weight makes it easier to fine-tune the time period of the pendulum swing, which ultimately controls the clock's accuracy. With less weight on the pendulum bob, I am able to use much less weight to drive the clock gears.

I found it difficult in the limited space of the tower shaft to prevent the weight from interfering with the pendulum without building a separating wall between them all the way down to the floor. Instead, I used a pair of eye hooks attached to the underside of the train table to offset the weight to a safe distance. This worked very well to eliminate pendulum interference, but it meant that the weight could only be raised to the underside of the display table instead of being allowed to descend the full height of the clock tower, meaning that the clock must be wound more frequently. Instead of chopping a hole in one of our full-size 40"x40" train tables, I built a small shelf unit that bolts onto the side of another table. This shelf was attached to an inside corner of one of our access holes.

The clock seems to be running very close to the correct time, but I am still fine-tuning the pendulum. The clock was typically running within 3-5 minutes of the correct time for the duration of the two-day train show, but it did not run for any continuous stretch of more than perhaps two hours without requiring maintainance and re-setting. At the present gear ratio, the weight drops about one foot per hour as it powers the clock mechanism. This means that the clock must be wound every two or three hours when displayed on a short table, such as those used by NELUG. The clock can be wound one of two ways: either the clock can be opened and the string wound back into the clock, or the excess string can simply be wound onto a reel on the weight, raising it back up toward the clock.

I am currently looking for a famous real-life clock tower to model the architecture of. I hope to find a clock whose real-life scale is close to the current minifig scale of this building, since there is no reason to create a gigantic building to house this mechanism.

I would also like to mention that Amnon Silverstein maintains a site containing a comprehensive index of LEGO clock designs that I wish I had found much earlier in my quest to build this clock.

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