French Quarter Hour Striking Clock

In English case, brass plaque on back says:

London, October 17, 1877
I bought this clock of
Elkington & Co.
Edward Livingston Davis

Movement approximately 3-3/4 inch diameter

Case dimensions: 17 inches H, 14-1/2 W, 7-3/16 D

5-1/2 inch dial, silvered brass, painted numerals and time track.

Measured mainspring dimensions

T: 22.3 mm wide (7/8 inch), 0.0138 – 0.014 inch thick, 54 inches long

S: 22.5 mm wide (7/8 inch), 0.013 inch thick, 46 inches long.

The strike mainspring has been shortened, so I calculated the proper size.

Mainspring thickness formula:

L = pi (B squared – A squared) / 2 T

L = Length
B = Barrel inside radius
A = Arbor radius
T = Thickness

Time Barrel
B = 18 mm
A = 5.8 mm
Optimum calculated length: 51.3 inches
The spring was 54 inches long, it looked very old and had no problems, so it was left alone.

Strike Barrel
A = 18,9 mm
B = 6.5 mm
Optimum calculated length: 59 inches
The spring is only 46 inches long, so it must be replaced.

Looking in the R & M catalog, there were springs of .012, .0125 and .013 inches thick that looked correct for the clock. Since new spring are stronger than old springs, I chose the thinest spring, .012″. I felt that there was only a very small chance that this spring would be too weak.

I calculated the optimum length for a .012 inch thick spring: 63.9 inches.

The spring in the catalog is 7/8 inches wide, 0.012 inches thick, 61 inches long. It is shorter than optimum, but considering that a much shorter spring had worked in the clock before, and based on past experience that 8 French clocks are often designed to run around 2 weeks on a winding, I used this spring. It is being tested now, and after 9 days, the striking has not slowed down significantly.

Strike setting up: There must be only a very small run after the last hammer drops, otherwise the quarts will not be struck correctly.

My job 4353.

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