Back to the Home Page
This is a brief description of a turret clock and how it works. I wrote this for the catalogue of ......
Sorry no graphics as yet, but read this in conjunction with the Turret Clock Keepers Handbook. There is a link on the home page.
Back to the Home Page
Visit to a clock
The Turret Clock
Stands the church clock at ten to three?
And is there honey still for tea?
So wrote Rupert Brooke of the church clock at Granchester which remained stopped at that time for many years. Perhaps this poem is about as close as most people get to a church clock. Yet located behind clock dials, aloft in dark church towers, or in garrets brooding over long-quiet stable blocks are some very interesting mechanisms. Known as turret clocks, or sometimes tower clocks, these clocks are usually seen only by those who wind them, but they really can be most fascinating. So come along, let's take an imaginary journey up a church tower and see what it's really like...
Up the Tower
We enter a low door at the bottom of the tower and there in the cramped entrance a gloomy stone spiral staircase winds its way upwards out of our sight. The steps are worn and uneven, narrow slit windows at every turn let in much-needed light, and it's rather cool and a bit dusty An odd cobweb or two adds to the feeling that not many people pass this way.
The Ringing Chamber
The first door we meet opens into a room where the bell-ringers perform. Hanging down from the ceiling are eight bell-ropes, and a notice clearly declares:
DO NOT TOUCH
Above us we can now just make out the muffled sound of the
clock ticking, a steady deep clunk every second, like the sound
of a very old grandfather clock. Swinging through a slot in the
ceiling we can just see the bottom of the clock pendulum. It is
the size of a dinner plate, fairly thick, and held on to the pendulum
rod by one of the biggest nuts we have ever seen.
In the Clock room
Moving on up the spiral staircase from the ringing room we come to the clock room. Lit by a single rather feeble bulb we see against a wall what looks like a wooden garden shed. The tick is now much louder and emanates from inside. Opening the wooden clock case we now see the clock itself, an iron frame filled with gear wheels, at the back is the top of the pendulum swinging from side to side. The clock mechanism is properly known as a movement. More about how it works later, but what we can see of the movement seems to indicate that it is very old.
Right in the front of the movement is clock dial, a bit unusual
since the figures run backwards - and it only has one hand. A
rod runs from the clock straight upwards to a set of gears on
the ceiling above, from there another rod runs across the room
to the back of the dial. A thin wire extends from the clock case
to the ceiling, going right up to the belfry where it operates
the hammer to strike the hours. Two steel ropes also come out
of the clock case, pass upwards, over pulleys, and then dive off
into the dark corners of the clock room. Looking closer into these
corners reveals that the ropes have huge cylindrical weights hanging
from them, each are about three feet tall, and a foot in diameter.
These provide the driving power for the clock and for the striking
as well. Below each weight is a hole in the floor, and it is down
these holes that the weights descend - right down to the ground
floor. Fortunately some guards round the holes protect the unwary
visitor from further detailed inspection.
Behind the Dial
Looking up to where the leading-off rod reaches the wall we see some gears known as the motion work. These gears are situated inside the tower and right behind the dial. They reduce the one-turn per hour of the minute hand into one turn in twelve hours of the hour hand. Small weights on the end of arms stick out at odd angles to counter-balance the weight of the hands outside. From the motion work on the wall a tube to the hands outside runs through a hole in the tower wall, in fact the hole is a small window, and the wall is very very thick about four feet! A chink of sunlight from outside illuminates the back of the dial, it is green in colour, so we know that this dial is made from copper sheet.
In the Belfry
Proceeding further up the staircase, we open another door and are treated to a flurry of dust in our faces. Outside the wind can be clearly heard, a reminder that we are now getting near the top of the tower. We are now in the belfry itself, we look in and see the bells, dull green as seen in the sunlight streaming in through the louvres - the open slats which allow the sound to escape whilst keeping the rain out. Belfries can be very dangerous places, so we do not go inside, but just pause to look in. Suddenly a bell starts to sound, the clock is striking the hour. A few pigeons perched outside the tower are startled and take off, their wings making a frantic clapping noise. The note of the bell is very loud and deep, and since we are so close it seems to be quite harsh. As the last stroke has sounded the bell goes on humming and humming, softer and softer until after a minute it has died away completely.
A fine View
Finally up the stairs once more, though a door where we have to bend almost double and then.... we are out on the roof to admire the view. After taking our breath we return down the stairs, and realise just how far we have come up. Then ducking down to avoid bumping out heads, we are again back at the bottom of the tower where we started.
We have experienced a turret clock.
Enjoy the visit? Well, if you want to go up a tower to see a clock for yourself, please get permission and go with someone; towers can be dangerous.
Who Needs a Turret Clock?
Why do turret clocks exist? Where ever man has a need to gather together, then some form of keeping time is needed to regulate when the meeting takes place. These gatherings may be for worship, for work, or just for pleasure.
In Mediaeval times religious services in churches and monasteries were probably the reason why the clock was invented. Monks had rise in the morning, to attend many services a day, to eat together, and then to bed. Bells were tolled to call the monks to worship. Indeed it is from the Latin word for bell - clocca, that the name clock is derived. No one knows who invented the first clock, or where, or when. However there are some things we do know; one of these is that during a night in 1198 there was a fire in the Bury St. Edmunds Abbey. Monks put the fire out using their cowls, water from the well and water from the clock; so the Abbey had a water clock!
The Clock is Born
Mechanical clocks as we would recognise them, first made their appearance about 1275. At first these clocks hung on a wall and had an alarm to wake a monk who would then go and ring a bell in the tower to summon his brothers. At some point the clock was made larger so that it had enough power to strike a bell in a tower ..... and the turret clock was born. One famous example of an early turret clock was at Salisbury Cathedral. Here in 1386, a man called Reginald Glover had to take care of the clock in the belfry as part of a legal contract. Some people say that the old clock on display in the cathedral today is the same clock referred to in the 1386 document, and so it is the oldest clock in the country. Such a claim is difficult to prove (or indeed to disprove!).
Turret clocks spread throughout churches, monasteries and royal palaces, all places where they was a large number of people working together. When country houses were built turret clocks were almost always put up, usually over the stable block. Here they would have kept time for the whole estate, regulating the life of all from the youngest stable lad to the lord himself.
Army and Navy barracks too had turret clocks. When factories started to be set up during the early 19th century turret clocks again appeared on these buildings to summon the workers, and to dismiss them at the end of the day.
In the village, like the town, the church clock regulated the affairs of people meeting together. "Run down to the church and tell me the time" a mother would say to her child. It did not matter if the youngster took a while to get home, accuracy was just not that important.
Turret clocks were set from a sundial, this meant the clocks in towns throughout the country did not tell the same time due to being at different longitudes. Differences across the UK could be up to 15 minutes, but this was quite accurate enough for local use since no one could travel fast enough to suffer. In the early 19th century when trains started to run across the country, correct time started to become important so Railway Time was used as a standard, and after this Greenwich Mean Time.
Less Need for Turret Clocks
It wasn't until late in the 19th century that the church clock declined in importance. Thanks to imports of cheap pocket watches from America, many people started to use their own time-piece. Wrist watches appeared on the scene around the time of the First World War: and their greater convenience led to an even further decline in the need for public clocks.
Today time is easily available to us all. Radio broadcasts the pips, Breakfast TV has its own little clock, teletext too has a continuous display of the time. Finally the amazing accuracy of quartz watches along with their low cost, really means that the turret clock is no longer really needed - it is out of date.
Regarded by All
But turret clocks still tick on, even though there is no real need for public time service they once provided. Loved by most people, they are taken care of: who would think of doing away with Big Ben, the clock on the Horseguards or the clock in the local Town Hall or church? Rather than do away with turret clocks there is a growing move to preserve our unique heritage which is so often hiding behind a dial.
How Clocks Work
Ever wondered how a clock works? - let's have a closer look at the clock we visited to answer that question.
The Going Train
Starting with the outside dial, the minute hand goes round once in 60 minutes. The minute hand is driven by the leading-off work - that is the rod which comes from the clock movement. In the clock movement the leading-off rod is driven by a wheel called the centre wheel which turns once per hour. A 'scape wheel is part of a train of gear wheels which is usually three in number. The last wheel in the train, and the smallest, is called the escapement wheel or the 'scape wheel for short. This wheel rotates a lot faster than the others, usually about once or twice a minute, and is linked to the pendulum through the escapement, a device which allows one tooth of the wheel to escape for every swing of the pendulum. So as the pendulum beats time it controls the speed at which the 'scape wheel rotates, and hence through the train of gears with the appropriate numbers of teeth, it allows the centre wheel to turn once in an hour; so too the minute hand turns once in 60 minutes.
A pendulum swings with a regular number of beats per minute, the number depends only on the length of the pendulum. A pendulum 39 inches long does one swing in one second, but a pendulum 14 feet long takes two seconds to make a single swing. In turret clocks most pendulums are somewhere between these two lengths.
Let's take another look at the escapement since that mechanism performs two tasks. Apart from releasing the 'scape wheel every swing of the pendulum the escapement also gives the pendulum a little push every beat to keep it swinging. If it was not for the little impulse the pendulum would not keep swinging and the clock would stop. The power to turn the hands, drive the train of gear wheels, and to keep the pendulum swinging, comes from a large weight. This weight hangs from a rope which is wound around a wooden drum in the clock known as a barrel. Mounted on the barrel is the great wheel, the largest gear wheel in the clock, this drives the centre wheel. So power from the falling weight is fed to the dial, the train of gears and the pendulum. All the gears in the section which work the hands are called the going train.
Turret clocks are wound up with a crank-handle which fits onto a square on the end of the barrel spindle. Since some clock weights can be more than half a ton, winding a turret clock can be very hard work.
Most turret clocks strike the hour on a bell, it is the striking train which operates the bell hammer. A lever in the clock the striking train is pulled down and released once for each stroke of the bell, this lever pulls a wire which runs to the belfry above the clock. Here it lifts a heavy hammer which then falls on the outside of the bell. A few turret clocks have jacks who strike the hours, these are figures whose arms are moved to sound the bells. Wimborne Minster has a jack who is dressed as a grenadier guard, he sounds the quarter-chimes from his position high up outside the tower.
Both the going train and striking trains are very similar, the striking train is also powered by a weight, but it is usually larger than the one on the going train. There is no escapement in the striking train, but a two-bladed fly revolves rapidly to control the speed of striking, the fly blades beating the air to control the speed of striking. In order to strike the correct number of blows one of two devices are used, a count-wheel or a rack. A count-wheel has notches at different interval round its edge, these are spaced so that the striking train will run first for one blow and stop, then, when set off at the next hour, it runs for two blows and stops; and so on up to twelve 'o clock. With rack striking, the rack, which looks like a section out of a gear wheel, is raised by one tooth every blow of the bell, when it is fully raised the striking stops. To control the correct number of blows the rack is allowed to drop the right amount by a specially-shaped cam which is sometimes called a snail. Have a look at one and you will see why it is called a snail!
Some clocks strike every quarter hour, either a tune like the Big Ben chimes or they sound a number of ding-dongs on two bells. The quarter train is almost identical to a striking train, here the main difference is the number of bell hammers it operates.
Another device was sometimes connected to a turret clock, a carillon. The carillon played tunes on the tower bells, hymn tunes were popular, so were national tunes and God Save the Queen - or King, as the case was at that time. Carillons were separate to the clock, looked rather like a clock mechanism, but had a large drum with pins in which operated the bell hammers. The whole mechanism is rather like a huge musical box and was usually set off by the clock only at certain times of the day.
Turret Clock Frames
All the gear trains are built into a frame, and together the whole mechanism is called a movement. Movements come in all different shapes, ages and designs; sizes could be as small as eight inches long, Big Ben is over sixteen feet long!
Turret clocks are given different names to describe them. Single train movements are ones that only drive a dial, two-train movements drive a dial and strike the hours, and three-train movements. which drive a dial and strike both the hours and the quarters.
How Turret Clocks Developed
Foliot Controlled Clocks
We have all seen a pendulum, this device was not applied to house clocks until 1656, and to turret clocks a few years later. Before this date a device known as a foliot was used instead of a pendulum. Shaped like a cross, the foliot was hung from its top, and had a weight at each end of the cross piece. The clock had a verge escapement which first pushed the foliot in one direction until a tooth was released, then in the opposite direction until another tooth was released; and so on. The foliot with its verge escapement was probably not a very good timekeeper by today's standards - the errors could have been about 15 minutes a day. Clocks from this period just struck the hour on a bell, but a few had a small outside dials with just an hour hand.
As previously mentioned the gear trains, going, striking were contained in a frame. When turret clocks first made an appearance the frame was made of wrought iron, that is iron which is hammered to the required shape whilst it is red-hot. In the same manner the wheels in the trains were also made of wrought-iron; the two trains being set in line with each other, or end-to-end as it is known. Many people think that the village blacksmith was the person who made such clocks; this not correct. Clock makers, or great clock makers (great refers to the size of the clock not to the clock maker) were the specialists who did the work and were very skilled as blacksmithing.
Early Pendulum Clocks
After 1670 the trains were moved to be side-by-side and the name birdcage is often used to describe the type of frame of these clocks. This alteration came about a little time after the invention of the pendulum was applied to the clock. William Clement in was credited with the invention of the anchor or recoil escapement, this was an important discovery which meant that timekeeping accuracy was improved to a minute or so per day. Wrought-iron was still used for making the clock frame and wheels. From about 1700 onwards makers started to employ brass to make most of the clock wheels. Outside dials become common, some had just one hand, but a few had both hour and minute hands.
Around 1800 improved smelting and founding techniques meant that clock frames and components could be made from cast iron. This meant that they became much stronger and were cheaper and quicker to produce. Brass too was easily available. As a result of these developments the four-poster frame was born, so called because of the round corner posts making it look a bit like a four-poster bed. With better quality materials, improved escapements such as the dead-beat invented by George Graham in 1717, clocks kept better time, loosing or gaining about a minute a week. Dials now commonly had hour and minute hands, and quarter chiming was heard more and more from clock towers.
The Flat Bed
Many inventions were made in the 19th century, the field of turret clocks was no exception. A great clock was needed for the new Houses of Parliament, and the one designed by Lord Grimthorpe was like nothing seen before. Firstly the frame was a flat bed made of cast iron. All the wheel bearings were bolted directly onto a horizontal flat frame, this meant it was much easier to manufacture, to assemble and to service the clock movement. Timekeeping improved to a second or so in a week, a really great performance for such a great clock. Two inventions gave this good timekeeping; firstly the pendulum was compensated so that changes in temperature did not affect its length, and secondly a double three-legged gravity escapement was used. Lord Grimthorpe invented this escapement so that it fed a constant amount of energy to the pendulum to ensure good timekeeping. Before this escapement was used, poor timekeeping was caused by the effect of wind, rain, ice and snow on the dial.
In the late 19th century turret clocks to the design of Lord Grimthorpe were made in Steam Clock Factories, so called because they had steam engines to power the machinery. These movements were mass-produced, and usually it is very easy to be able to tell who the maker was.
Regional variations in designs are found through out the country for all periods. From about 1600 to 1750 wood was sometimes used for frames, particularly in an area generally covered by the Midlands, East Anglia and Lincolnshire. The names of these frame types really describe the shapes; door-frame and field-gate.
The 20th Century
Little changes to turret clocks were made at the start of the 20th century, but electric clock movements were used more, the last large mechanical turret clock was made about 1960. Two types of electric turret clock were used, one where the dial was impulsed every half-minute from a master clock, the other and most common one was the synchronous motor. Electric power is distributed by the National Grid, good timekeeping was available everywhere where there was electric power since the frequency of the alternating current was accurately controlled in the generating station by a master clock. Up in a tower the speed of the synchronous clock motor was kept in step with the speed of the generator. Over a 24-hour period the time was exact, but variations of up to half a minute during the day could be expected due to changes in demand for electric power, perhaps caused by millions of electric kettles switched on at the end of Neighbours.
In the last 20 years some mechanical turret clocks have been converted to auto-winding, electric motors were fitted to do away with the heavy task of clock winding. Sadly some of these conversions were badly done leaving the clock with many parts missing, or even completely replacing the trains with an electric motor. Today, fortunately, the companies which did such work are more sympathetic and clock-wrecking does not occur so often.
New Life for Turret Clocks.
Today turret clock making is still carried out, but now special clocks are popular. Situated in shopping malls or city centres, these clocks have interesting automata - figures which perform every time the clock strikes. A recent clock made features a lion holding the clock dial. On the hour the lion's head and eyes move, his tail strikes the bell and a coconut falls from a palm tree. Monkeys swinging in the palm tree strike the quarters for the amusement of the watchers.
More and more people are interested in history and its preservation. Turret clocks are out of sight in their towers and often out of mind, this means that they can get neglected, damaged by inexperienced maintenance, and in some cases - lost for ever.
Honey still for Tea.....
Stands the church clock at ten to three?
And is there honey still for tea?
The clock at Granchester church no longer stands still at ten to three, it is working well. Turret clocks can be more romantic that the cold iron they are made from. Look at all the history! the people who wanted the clock, the maker who made it, the benefactor who paid for it and the many events the dial has peered down upon. Perhaps a poet to follow Rupert Brooke is needed to put these things to verse.
Back to the Home Page