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More than 130 years after its installation atop the Cambridge City Hall, a mechanical tower clock — wound by hand each week — continues to chime. Crimson photographers followed David W. Graf, the clock’s steward for the past 30 years, as he wound the clock for the last time before the building undergoes a 15-month facade restoration.

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Nestled in a nearly 160 foot tower, the clock is the second largest model to be made by E. Howard & Co., and its pendulum descends 14 feet beneath the mechanism itself. The bottom of the pendulum — which weighs around 200 pounds — can be seen encased in wood and supported by a structural beam.

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Rusted and completely nonfunctional at the time, the clock was commissioned for restoration in 1994 — almost exactly one century after it was first installed. Graf, a craftsman specializing in tower clock restoration and repair, was hired by the City of Cambridge to restore the clock to working condition.

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To bring the clock back to life, Graf manufactured more than 150 missing pieces by hand, precisely designing and machining them to replicate original parts.

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In addition to repairing the internal mechanics, Graf also restored the clock frame, pinstriping and hand-painting the original flower motifs to restore its color and character.

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While restoring the tower clock, Graf used the South Station clock — also made by E. Howard & Co. — as a reference, taking photographs and making measurements to design missing pieces.

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The double three-legged gravity escapement mechanism, coupled with the pendulum, keeps the clock running precisely. Built to be impervious to external forces, the structure is composed of iron and steel. Inside the pendulum shaft, a hollow brass sleeve expands and contracts in response to temperature changes, maintaining a constant center of gravity.

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The center shaft keeps the minute hand of the clock running at one minute per revolution, while a set of 1:12 reduction gears drives the hour hand.

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Following the clock’s restoration, Cantabrigians were surprised to hear the bell return to its normal ringing schedule. After residents complained about the sound keeping them awake at night, Graf installed a mechanism that stopped the clock from ringing between 9 p.m. and 9 a.m. without altering or damaging the clock’s existing structure.

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Above, a metal tube extends from the internal mechanism to one of the four clock faces that adorn the tower.

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Since finishing the clock’s restoration in 1995, Graf has returned to the Cambridge City Hall each week to wind the mechanism and make sure that it is running smoothly. For the past 25 of these years, Graf has been commuting from his home in Maine, also stopping to wind other clock towers in Cambridge, Belmont, and Arlington.

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The manual winding of the clock’s weights each week powers the gravity escape mechanism, which converts the gravitational force of the weights into rotational motion.

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The bell, located just above the clock mechanism at the top of the tower, weighs two tons.

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The weekly winding also powers the hammer of the bell, which strikes on the hour and reverberates across the city.

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As Cambridge City Hall begins a facade restoration project, the tower clock has been temporarily stopped. Graf will be re-gilding the clock tower face as part of the restoration.

When the restoration is complete, the clock will resemble its original self more closely than ever before. Still, its future remains uncertain, as a move towards electrification and declining interest in tower clocks endanger their continued preservation.

But for now, Graf will continue to keep the tower clock tolling.