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The Cotehele clock is situated at Cotehele House, Calstock, Cornwall. It is the earliest turret clock in the United Kingdom still working in an unaltered state and in its original position. It was probably installed between 1493 and 1521.
The first chapel at Cotehele House dates from around 1411, but only parts of the north and south wall of the original building survive.
Piers Edgcumbe inherited Cotehele House in 1489. He married Joan Durnford in 1493 and she died in 1521. He remarried in 1525. Two important altarpieces commemorate the union of Edgcumbe and Durnford, so it is likely that the building work on the chapel was carried out during the early years of their marriage from 1493 onward. The alcove that houses the clock was added into the west wall of the chapel (the plan below has north on the right, so the west wall is at the top of the drawing). The 2004 building report states that the west wall was probably rebuilt during the work carried out on the chapel. It is thus likely that the clock was installed at the chapel between 1493 and 1521, with more probability towards the earlier date.
The clock is acknowledged to be the earliest turret clock in the United Kingdom still working in an unaltered state and in its original position.[ citation needed ] It has no face, but is attached to a bell which strikes the hour.
Unlike its contemporaries, the Cotehele clock was never converted to pendulum, which makes it one of the older original verge escapement and foliot clocks. Other clocks with this claim, such as the Salisbury Cathedral clock, were converted and later retrofitted with a verge & foliot.
As the construction dates of the Salisbury and the Wells Cathedral clocks are disputed (they are most likely early 16th century clocks), the Cotehele Clock may well be the oldest working turret clock in the UK. Even though large numbers of turret clocks were installed in the 14th century, none of them survived. The unique circumstances at Cotehele house assured that the clock was not replaced and scrapped.
This alcove appears to be purpose-built for the clock as it has a chimney-like chute that goes up to the bell and has just the right dimensions for the clock, the weights, and the double-pulley system. It is unlikely that a second-hand clock would have been procured for such a splendid new building. Also, the clock is in very similar style to those at Castle Combe and Marston Magna.
The clock was taken apart and transported to Thwaites & Reed for restoration in 1962.
According to Cecil Clutton, the pinions were considered worn, but satisfactory, and they were left as found. Re-bushing was carried out in steel, and the clock was taken back to Cotehele and re-assembled.
The strike release mechanism was replaced during this overhaul, as the lever in place is stamped T&R and dated. Also, the wooden frame to which the clock is fixed seems to have been renewed.
The verge suspension also appears to be of newer date and looks similar in style to the new strike mechanism. It is possible that the verge was originally suspended from a string.
A conservation project was undertaken to return the clock and bells to working order in time for the Queen's Golden Jubilee in June 2002.
Peter Watkinson, turret clock maker and antique clock restorer, overhauled the clock. He dismantled and thoroughly cleaned its components, then applied grease and reassembled. If the weights are adjusted correctly, the clock tells accurate time to within a couple of minutes per day. The chime of the hour contributes greatly to the ambience of Cotehele, where it has remained for 500 years. The clock runs on two weights – one connects to the striking train and the other to the going train. Currently, the clock is started in the morning before opening time and stopped in the afternoon after closing time. Theoretically, the clock could run 24 hours on a full wind.
The striking train sits on top of the clock, the going train is below.
The frame is a two-post door frame made from wrought iron. The top and bottom horizontal bars are fixed to the vertical bars by wedged tenon.
The total frame height is 115 cm, and the iron bars which form the frame are approximately 4 cm wide and 1.5 cm thick.
The gear ratios are as follows:
The great wheel of the going train does one turn in 3600 seconds (1 hour), the escapement wheel takes 303.1579 seconds for one turn, and the foliot does one full swing in 12.1263 seconds, one half swing in 6.06317 seconds.
The foliot is 89 cm wide, with a grooved section of roughly 9 cm on either side. The left foliot side has 13 teeth, the right has 10 teeth to adjust the weights. The length of the verge is 56 cm. The lower verge pallet is 3.7 cm high, the upper pallet is 3 cm high. Both are approximately 2 cm wide. The pallets are at a 110° angle.
The escapement wheel has an outer diameter of 28 cm, and a width of 4 cm including the teeth. It has 4 spokes, each roughly 2 cm wide and 7mm thick.
The going train is wound with a capstan with 4 spokes. Theoretically, the rope could be wound 24 times around the barrel without having to layer it, thus enabling the clock to run for a full day and night without winding. The winding mechanism has a ratchet for the barrel.
It is interesting that if the great wheel had 96 teeth instead of 95, the gear ratio would have been a lot more logical and would have resulted in exactly 12 seconds for a double swing. This points again to a manufacturing date in the late 15th century, as minutes and seconds were not used in clock making and only the concept of an hour was known.
Also, the very short section of the foliot that allows weight adjustment makes it clear that this clock was never used for unequal hours (12 hours from sunrise to sunset, making hours shorter in winter and longer in summer), but was always used to measure equal hours and probably run 24 hours per day. The shortness of the grooved outer sections would not allow the clock to strike 12 times within 8 hours in winter or 12 times within 16 hours in summer.
The great wheel of the striking train has 78 teeth and 8 pins that operate the bell lever. The gearing for the count wheel is:
This corresponds to the 78 strikes the clock has to make in 12 hours
The gearing for the fly is as follows:
The count wheel turns once in 12 hours, the big wheel turns 9.75 times in 12 hours, thus striking the bell 78 times in 12 hours, and the flail arbor turns once every strike of the bell, and the fly turns 3.333 times per strike of the bell.
The count wheel has 78 teeth on the outside, and the 12 notches are on the inside of the count wheel. The main arbor has an 8 teeth pinion which drives the count wheel. This directly reflects the ratio of strikes to lifting pins on the main wheel, as each turn of the count wheel has to produce 78 strikes ( 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 = 78). One turn of the count wheel = 9.75 turns of the big wheel.
The barrel of the striking train can take the necessary 19.5 windings of rope to produce the 156 strikes necessary to run a full 24 hours.
The going train has a stone weight, and the striking train an iron weight. The striking train weight roughly weighs 40 kg, the going train stone weight is slightly heavier. As the weights use a double-pulley system, they descend by half the rope given by the clock, and exercise a force of half their weight on the clock.
The accuracy of the clock was measured on 5 May 2011 for a period of 3 hours and 22 minutes. The clock's accuracy varied from +10 to -40 seconds, but it is very hard to make any predictions on the day-to-day accuracy of the clock.
There is no pattern that is repeated every 60 minutes, but this might well have to do with the fact that the gear ratio of the going train is 95:8, meaning that it takes a full 8 hours until the same teeth on the escapement wheel pinion and the great wheel engage again. A longer measuring interval (24 hours) might be necessary to observe repeat patterns.
There are a couple of factors that influence the accuracy of the Cotehele Clock:
Considering that sundial time varies +- 15 minutes throughout the year, the Cotehele clock was a perfect instrument for measuring time in the 15th and 16th century. If run 24 hours a day (the strike can be turned off at night), it only needed adjusting every couple of days at noon with the help of a sundial whenever the sun was out. Even if the sun wasn't visible for a longer stretch of days, the clock would still keep good enough time if it was wound fully once per day.
A pendulum clock is a clock that uses a pendulum, a swinging weight, as its timekeeping element. The advantage of a pendulum for timekeeping is that it is an approximate harmonic oscillator: It swings back and forth in a precise time interval dependent on its length, and resists swinging at other rates. From its invention in 1656 by Christiaan Huygens, inspired by Galileo Galilei, until the 1930s, the pendulum clock was the world's most precise timekeeper, accounting for its widespread use. Throughout the 18th and 19th centuries, pendulum clocks in homes, factories, offices, and railroad stations served as primary time standards for scheduling daily life, work shifts, and public transportation. Their greater accuracy allowed for the faster pace of life which was necessary for the Industrial Revolution. The home pendulum clock was replaced by less-expensive synchronous electric clocks in the 1930s and '40s. Pendulum clocks are now kept mostly for their decorative and antique value.
The grasshopper escapement is a low-friction escapement for pendulum clocks invented by British clockmaker John Harrison around 1722. An escapement, part of every mechanical clock, is the mechanism that gives the clock's pendulum periodic pushes to keep it swinging, and each swing releases the clock's gears to move forward by a fixed amount, thus moving the hands forward at a steady rate. The grasshopper escapement was used in a few regulator clocks built during Harrison's time, and a few others over the years, but has never seen wide use. The term "grasshopper" in this connection, apparently from the kicking action of the pallets, first appears in the Horological Journal in the late 19th century. The term “escapement” is not really applicable here, since the wheel never escapes the pallets: there is always a tooth in contact, so there is never a short period where the wheel “escapes” and free-wheels forward to impact the other pallet.
An escapement is a mechanical linkage in mechanical watches and clocks that gives impulses to the timekeeping element and periodically releases the gear train to move forward, advancing the clock's hands. The impulse action transfers energy to the clock's timekeeping element to replace the energy lost to friction during its cycle and keep the timekeeper oscillating. The escapement is driven by force from a coiled spring or a suspended weight, transmitted through the timepiece's gear train. Each swing of the pendulum or balance wheel releases a tooth of the escapement's escape wheel, allowing the clock's gear train to advance or "escape" by a fixed amount. This regular periodic advancement moves the clock's hands forward at a steady rate. At the same time, the tooth gives the timekeeping element a push, before another tooth catches on the escapement's pallet, returning the escapement to its "locked" state. The sudden stopping of the escapement's tooth is what generates the characteristic "ticking" sound heard in operating mechanical clocks and watches.
In horology, a movement, also known as a caliber or calibre, is the mechanism of a watch or timepiece, as opposed to the case, which encloses and protects the movement, and the face, which displays the time. The term originated with mechanical timepieces, whose clockwork movements are made of many moving parts. The movement of a digital watch is more commonly known as a module.
A mainspring is a spiral torsion spring of metal ribbon—commonly spring steel—used as a power source in mechanical watches, some clocks, and other clockwork mechanisms. Winding the timepiece, by turning a knob or key, stores energy in the mainspring by twisting the spiral tighter. The force of the mainspring then turns the clock's wheels as it unwinds, until the next winding is needed. The adjectives wind-up and spring-powered refer to mechanisms powered by mainsprings, which also include kitchen timers, metronomes, music boxes, wind-up toys and clockwork radios.
In horology, the anchor escapement is a type of escapement used in pendulum clocks. The escapement is a mechanism in a mechanical clock that maintains the swing of the pendulum by giving it a small push each swing, and allows the clock's wheels to advance a fixed amount with each swing, moving the clock's hands forward. The anchor escapement was so named because one of its principal parts is shaped vaguely like a ship's anchor.
The vergeescapement is the earliest known type of mechanical escapement, the mechanism in a mechanical clock that controls its rate by allowing the gear train to advance at regular intervals or 'ticks'. Verge escapements were used from the late 13th century until the mid 19th century in clocks and pocketwatches. The name verge comes from the Latin virga, meaning stick or rod.
A balance wheel, or balance, is the timekeeping device used in mechanical watches and small clocks, analogous to the pendulum in a pendulum clock. It is a weighted wheel that rotates back and forth, being returned toward its center position by a spiral torsion spring, known as the balance spring or hairspring. It is driven by the escapement, which transforms the rotating motion of the watch gear train into impulses delivered to the balance wheel. Each swing of the wheel allows the gear train to advance a set amount, moving the hands forward. The balance wheel and hairspring together form a harmonic oscillator, which due to resonance oscillates preferentially at a certain rate, its resonant frequency or "beat", and resists oscillating at other rates. The combination of the mass of the balance wheel and the elasticity of the spring keep the time between each oscillation or "tick" very constant, accounting for its nearly universal use as the timekeeper in mechanical watches to the present. From its invention in the 14th century until tuning fork and quartz movements became available in the 1960s, virtually every portable timekeeping device used some form of balance wheel.
The lever escapement, invented by the English clockmaker Thomas Mudge in 1754, is a type of escapement that is used in almost all mechanical watches, as well as small mechanical non-pendulum clocks, alarm clocks, and kitchen timers.
A striking clock is a clock that sounds the hours audibly on a bell, gong, or other audible device. In 12-hour striking, used most commonly in striking clocks today, the clock strikes once at 1:00 am, twice at 2:00 am, continuing in this way up to twelve times at 12:00 mid-day, then starts again, striking once at 1:00pm, twice at 2:00 pm, up to twelve times at 12:00 midnight.
A fusee is a cone-shaped pulley with a helical groove around it, wound with a cord or chain attached to the mainspring barrel of antique mechanical watches and clocks. It was used from the 15th century to the early 20th century to improve timekeeping by equalizing the uneven pull of the mainspring as it ran down. Gawaine Baillie stated of the fusee, "Perhaps no problem in mechanics has ever been solved so simply and so perfectly."
The Salisbury Cathedral clock is a large iron-framed tower clock without a dial, in Salisbury Cathedral, England. Thought to date from about 1386, it is a well-preserved example of the earliest type of mechanical clock, called verge and foliot clocks, and is said to be the oldest working clock in the world, although similar claims are made for other clocks. Previously in a bell-tower which was demolished in 1790, the clock was restored to working condition in 1956 and is on display in the North nave aisle of the cathedral, close to the West front.
St Mark's Clock is housed in the Clock Tower on the Piazza San Marco in Venice, Italy, adjoining the Procuratie Vecchie. The first clock housed in the tower was built and installed by Gian Paolo and Gian Carlo Rainieri, father and son, between 1496 and 1499, and was one of a number of large public astronomical clocks erected throughout Europe during the 14th and 15th centuries. The clock has had an eventful horological history, and been the subject of many restorations, some controversial.
In mechanical horology, a remontoire is a small secondary source of power, a weight or spring, which runs the timekeeping mechanism and is itself periodically rewound by the timepiece's main power source, such as a mainspring. It was used in a few precision clocks and watches to place the source of power closer to the escapement, thereby increasing the accuracy by evening out variations in drive force caused by unevenness of the friction in the geartrain. In spring-driven precision clocks, a gravity remontoire is sometimes used to replace the uneven force delivered by the mainspring running down by the more constant force of gravity acting on a weight. In turret clocks, it serves to separate the large forces needed to drive the hands from the modest forces needed to drive the escapement which keeps the pendulum swinging. A remontoire should not be confused with a maintaining power spring, which is used only to keep the timepiece going while it is being wound.
The Riefler escapement is a mechanical escapement for precision pendulum clocks invented and patented by German instrument maker Sigmund Riefler in 1889. It was used in the astronomical regulator clocks made by his German firm Clemens Riefler from 1890 to 1965, which were perhaps the most accurate all-mechanical pendulum clocks made.
A turret clock or tower clock is a clock designed to be mounted high in the wall of a building, usually in a clock tower, in public buildings such as churches, university buildings, and town halls. As a public amenity to enable the community to tell the time, it has a large face visible from far away, and often a striking mechanism which rings bells upon the hours.
A mechanical watch is a watch that uses a clockwork mechanism to measure the passage of time, as opposed to quartz watches which function using the vibration modes of a piezoelectric quartz tuning fork, or radio watches, which are quartz watches synchronized to an atomic clock via radio waves. A mechanical watch is driven by a mainspring which must be wound either periodically by hand or via a self-winding mechanism. Its force is transmitted through a series of gears to power the balance wheel, a weighted wheel which oscillates back and forth at a constant rate. A device called an escapement releases the watch's wheels to move forward a small amount with each swing of the balance wheel, moving the watch's hands forward at a constant rate. The escapement is what makes the 'ticking' sound which is heard in an operating mechanical watch. Mechanical watches evolved in Europe in the 17th century from spring powered clocks, which appeared in the 15th century.
The history of timekeeping devices dates back to when ancient civilizations first observed astronomical bodies as they moved across the sky. Devices and methods for keeping time have gradually improved through a series of new inventions, starting with measuring time by continuous processes, such as the flow of liquid in water clocks, to mechanical clocks, and eventually repetitive, oscillatory processes, such as the swing of pendulums. Oscillating timekeepers are used in all modern timepieces.
In horology, a wheel train is the gear train of a mechanical watch or clock. Although the term is used for other types of gear trains, the long history of mechanical timepieces has created a traditional terminology for their gear trains which is not used in other applications of gears.
The Castle Combe clock in St. Andrew's Church, Castle Combe, Wiltshire, England was probably made in the late 15th century. It is faceless and strikes a bell in the church tower.
50°29′45″N4°13′33″W / 50.49592°N 4.225964°W
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