Seth Thomas Adamantine Clock, Mahogany Finish, Back Escapement Movement

This beautiful Seth Thomas Adamantine mantel clock has a mahogany finish and two pillars on each side of the case. This clock has the 8-day movement with escapement in back, so it was made in 1901 or earlier. The case is 12 1/4 inches tall and 16 3/4 inches wide at the feet. The minute hand is 2 1/8 inches long.

Repair job 5861. I polished the pivots, installed 7 bushings, and tightened the clock rivets. The back escapement movement uses a strip recoil escapement requiring a small pendulum arc. The pendulum arc when running is much larger than the minimum arc (escape arc), so these clocks are very reliable even when slightly off-level. These movements have fairly thick mainsprings (around 0.018 inch) that are 11/16 inch wide and not the standard 3/4 inch wide. If a mainspring does need replacing (it is best to keep the original springs) it is important to not use a spring that is too strong.

See more photos.

This example’s original mainsprings are the following sizes:

Time: 11/16 by 0.0187 inch

Strike: 11/16 by 0.0185 inch.

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