It seems to become customary that I visit some turret clocks when on vacation. In Italy in 2012, I had seen and photographed turret clocks at Lucca and Cardoso in Tuscany (please excuse that these postings are currently only available in German).
As this blog has "... and other machines" in its title, I'll now show a few photos and videos of three English turret clocks.
In England, I climbed the clock tower at St.Albans, the church tower at South Mimms, and finally the clock tower of St. Mary’s at Oxford. Each of the clocks I saw there is interesting on its own right.
Here are a few pictures and videos from the clock tower at St.Albans. Its clock has a Denison escapement, which was invented by Edmund Beckett Denison (who later called himself Edmund Beckett and became Lord Grimthorpe). The escapement is also known as "Westminster escapement," because the famous clock in Big Ben, which was designed by Edmund Beckett, uses it. Actually, there are different versions of this escapement: Big Ben has a double three-legged Denison escapement, whereas the clock at St.Albans has a single four-legged Denison escapement:
St.Albans clock tower, 25.8.2013
St.Albans clock tower, 25.8.2013
The following picture shows the clockwork.
The pendulum and escapement are not integrated in it, but are mounted on the opposite wall. A shaft that can be seen at the top goes from the clock mechanism to the escapement. Behind the shaft, one can see the large fly brake of the striking mechanism. Originally, the clock was of course wound manually, but like almost all mechanical clocks it has been converted to automatic electric winding. Therefore, the barrel left of the center no longer carries a rope. Rather, a chain—which can been seen above the barrel—connects the driving shaft with the motor winch, whose housing can be seen at the left:
Clock, St.Albans clock tower, 25.8.2013
Here is a still image of the escapement:
Single four-legged Denison escapement, St.Albans clock tower, 25.8.2013
The following two videos show the action of the escapement:
South Mimms's turret clock has a standard Amant escapement (a type of deadbeat escapement derived from the Graham escapement; in Germany, we call it "Mannhardt escapement" after a famous Bavarian clockmaker). When we visited the clock at South Mimms, it had unfortunately been out of order for a few days, as the winding mechanism had stopped working.
Here is the clockwork. In the center, one can see the shaft leading to the hands (with the hour hand gears at the far end). Also here, the barrels no longer contain ropes—rather, chains lead to motors on top of the clock housing that wind their own weights. The pendulum is at the back—one can see its heavy bearing frame behind the escapement. Two large air brakes can be seen at the back:
Clockwork, South Mimms, 26.8.2013
On top of the case housing the clockwork are the three winches. The two weights for the striking trains are on the right side of the clock, the weight for the clock train is apparently right below the clockwork. The picture also shows various levers redirecting wires to the bell strikers in the belfry above:
Winches and transmissions for bell wires, South Mimms, 26.8.2013
Winches and transmissions for bell wires, South Mimms, 26.8.2013
The central controlling mechanism of the clock is the escapement:
Amant escapement, South Mimms, 26.8.2013
Amant escapement, South Mimms, 26.8.2013
Here is the spring to which the pendulum is attached. On the right side, one can see the escapement wheel, whose teeth are flattened on one side. This allows them to pass by the rather thick pallets of the escapement:
Pendulum spring, South Mimms, 26.8.2013
The reduction gear for the hour hand is placed near the clock dial:
1:12 gears for minute and hour hands, South Mimms, 26.8.2013
Here are two pictures of the strike trains. At the back, one can see the air brakes necessary to control the striking.
Hour strike train, South Mimms, 26.8.2013
Half (or quarter?) hour strike train, South Mimms, 26.8.2013
The bells of the melody played are stroke by the teeth on this barrel—essentially, a small barrel organ, but with bells instead of pipes:
Bell striking barrel, South Mimms, 26.8.2013
But what had me totally confused was the missing count mechanism for the strikes. Essentially, there are two categories of striking mechanisms:
- The older (at least 500 years old) count wheel strike trains use a single wheel that has stops after 1, then 2, then 3, etc., and finally 12 strikes. Such a "count wheel" can be seen on the picture of the old clockwork at Cardoso, and also below at St.Mary's in Oxford.
- The more modern (less than 300 years old) rake strike trains use a toothed segment that falls against a spiral controlled by the hour wheel. A single or double toothed wheel pulls the segment back tooth by tooth, which produces the correct number of strikes. The new clockwork at Cardoso has such a strike train.
Disappointed, I pushed my camera to the back side of the clockwork and made a last shot using the flash—and here it is: The clock does actually use a count wheel, but it is very small. On the left side of this wheel, one can see three small pins; and when one counts the teeth first between the upper and the middle pin, and then the middle and the lower pin, one finds that there are eight notches above vs. seven notches below. So this is actually a tiny count wheel! One can also see that it is driven by a "two-teethed wheel," whose teeth are actually also simple pins. Therefore, one revolution of its shaft will produce two strikes:
Count wheel, South Mimms, 26.8.2013
Finally, here is the plaque on the front of the clockwork, which tells us the installation date:
Plaque, South Mimms, 26.8.2013
A day later, we went to Oxford, where I visited the splendidly restored clock at St. Mary’s. Here is the tower—unfortunately, I forgot to take a picture of the clock dial:
St. Mary’s Clock Tower, Oxford, 27.8.2013
The clock is behind a glass cover which doubles as a board for a few general explanations. In contrast to the previous two clocks, this one has not been converted to electric winding—it must be manually wound, as at the time when it was installed!
Clockwork, St. Mary’s Clock Tower, Oxford, 27.8.2013
Clockwork, St. Mary’s Clock Tower, Oxford, 27.8.2013
Because of the glass housing, the clockwork is a little difficult to photograph. Still, here are a few pictures of important parts.
The Amant escapement is similiar to the one in South Mimms:
Amant escapement, St. Mary’s Clock Tower, Oxford, 27.8.2013
Amant escapement, St. Mary’s Clock Tower, Oxford, 27.8.2013
The hour strikes are controlled by a typical large count wheel with inside teeth. This count wheel design is at least 400 years old—it can for example be seen in the picture of the old clockwork in Cardoso (see links above). A part of the count wheel can be seen in the following picture. The other wheel is coupled with a ratchet (the corresponding saw-toothed wheel can also be seen) attached to the barrel holding the rope:
Hour strike train with count wheel, St. Mary’s Clock Tower, Oxford, 27.8.2013
The quarter-chime train can be seen here—one can recognize the chime barrel with the teeth that move the levers on the right that lead to the bells; and the count wheel with the trapezoid cuts:
Quarter-chime train, St. Mary’s Clock Tower, Oxford, 27.8.2013
In the following picture, one can see the drive train of the air brake of the quarter-chime train. One of the blades of the brake can be seen standing vertically near the wall:
Quarter-chime train, St. Mary’s Clock Tower, Oxford, 27.8.2013
That's all from this year's turret clocks!
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