BULLE CLOCKS The InventorsThe Inventors Bulle electric clocks were developed in France just prior to the Great War of 1914-1918. It was at time in the early 20th Century that there was a great deal of activity throughout Europe, the UK and USA in developing domestic clocks which would operate on battery power. Two Frenchmen, working initially independently, on aspects of electric solenoids and clockwork mechanisms ultimately came together to create the Bulle clock. Professor Marcel Andre-Moulin gained a Science degree in 1904 and his Doctorate in Science in 1910. He became a lecturer in Chronometry at the Faculty of Science Bensancon and then was named Director of that Institute. By 1912 Andre-Moulin had developed the system of using a solenoid with a 3 pole tungsten magnet which, in 1914 he used to construct an electric clock. Maurice Favre-Bulle was born in Bensancon, into a family of clockmakers. He studied at l’Ecole d’Horolgerie de Bensancon from 1885 – 1888 before joining his brother in taking over and running the family clock factory Favre-Heinrich. During the Great War Favre-Bulle worked at the engineering laboratories of the Faculty of Sciences of Paris, developing military timers, watches, timing systems and telegraphy. At the end of the war Favre-Bulle joined with Marius Lavet to form La Societe Bulle et Cie, a company to develop prototype electric clocks. In 1920 a patent was taken out by Favre-Bulle for an electric clock. The patentees were Favre Bulle and Madame Veuve Andre-Moulin, the widow of Marcel Andre-Moulin. The commercial exploitation of this patent followed. In 1920 Compagnee Generale des Appareils Horo-Electrique was established to commence the commercial production of the Bulle clock. During the period 1920 to 1952 production is estimated to have been some 300,000 clocks. All used the contact system as outlined in the original patent and over 100 different case designs were utilised. As the years progressed the movement remained basically unchanged although new materials were introduced as they became commercially available, e.g. aluminium, Bakelite, chrome. Production was also started in England in 1934 and these clocks exhibited obvious differences to the French product, particularly in the direction of reducing the cost. This included lighter gauge metal, steel plate rather than brass, smaller half-arc magnets, etc. Favre-Bulle died in April 1954, aged 84. Production ceased as he had no descendants and transistor control of electric clocks was immanent thus making the Bulle technology redundant. The Clock and its Operation The Clock and its Operation The clock is based on the reaction between a permanent bar magnet and an electric coil, hence it is classified as an electromagnetic clock. In the Bulle clock the coil forms part of the swinging pendulum. When the pendulum is in motion, it makes and breaks electrical contact at the pin and the fork. Current flows for the split second of contact, activates the coil and produces a magnetic field around the coil. This magnetic field opposes the field in the bar magnet, which pushes (impulses) the coil, hence pendulum swings away from the central magnetic pole. The Bulle magnet is unique and hard to believe it can exist. Made of cobalt steel, in either an arc or U-shape, it has three poles ! This unique feature produces a very high magnetic field at the centre of the bar and at this point the lines of force are perpendicular to the axis of the magnet. When the coil is activated at the centre point of its swing, ie. the centre of the bar magnet, the coil’s field cuts the magnetic field to create the opposing reaction and drive the pendulum away. Please note that the diagram to the left is actually incorrect. The lines of force from the coil do not radiate outwards as shown (“Claimed”). The lines of force align themselves along the coil, and work at right angles to the magnet’s field (“Actual”). This is shown in the additional sketch. It is also worth noting that the unique magnet design is also its downfall. The design is such that eventual demagnetisation is a certainty, because the magnetic domains at the centre of the magnet are in constant opposition. Bulle Clock Technical Construction Details While it is not immediately apparent, the Bulle clock is polarity sensitive. If the battery is connected the wrong way around, the clock will not run. This is determined by the direction in which the coil is wound, and the magnet. The very first test of a newly acquired Bulle will reveal if the battery is connected properly. If the clock won’t run, try reversing the battery polarity first. Further work is needed only if this fails to make the clock work. The silver pin and the fork contact must be absolutely clean. Even a small amount of tarnish will stop the clock, because of the low voltage and minimal contact pressure.The silver pin and the fork contact must be absolutely clean. Even a small amount of tarnish will stop the clock, because of the low voltage and minimal contact pressure. Here you can see the sequence of events as the pendulum swings. The pin makes contact only with the uppermost corner of the fork contact, and the contact period is very short. I have measured it at ~190ms, although the actual time will vary somewhat depending on the way the clock has been set up. A small variation is to be expected, and it will also vary depending on the pendulum period (714ms for the one I measured, representing an 84 beat/minute pendulum). It is probable that if the contact duration is around 25% of the pendulum period the contacts are reasonably well adjustmed. Make sure that the silver contact spring, its rolling loop and the loop pin are also scrupulously clean. These points must never be oiled because the oil film can create an insulating barrier which will prevent current flow. Isochronism To compensate for variation in battery voltage, the Bulle clock is fitted with an isochronism corrector which, by its arrangement, causes a retarding force on the pendulum with each oscillation. This is zero to start with but increases with the amplitude and, adding to the force of gravity, enables the clock to maintain a constant rate in spite of amplitude variation. Note the gap in the end cheek of the coil former. These are made from brass, and would create a short-circuited turn if the gap were missing. This would introduce more than enough loss to stop the clock. Operating ExpectanciesBulle clocks were designed to run on 1.5 volts DC and, with the extremely low current draw, a modern alkaline D cell will last for over a year. If the clock will not operate on 1.5 volts then there is a problem in the circuit. The circuit is extremely simple with a battery, a switch and a coil all in series. The coil has a nominal resistance of 1100 – 1200 ohms derived from a winding of 0.071 mm enamelled copper wire. When operating normally the peak current drawn is typically 1.3 milliamps. The average current is a great deal lower, because the coil is only switched into the circuit very briefly. With a contact duration of 25% (typical), average current is 1/4 of the peak, or about 325uA (325 microamps, or 0.325 milliamp). When restoring a Bulle the mechanism is extremely simple but composed of many very small parts. The sequence of dismantling must be identically reversed for reassembly to ensure the clearances and components will operate correctly. The electric circuit may be simple but there are electrical connections throughout the circuit, ie. at the battery terminals, at the flexible connection, at the coil in and out terminals, at the two chassis connections, and the silver loop spring, all of which must be clean and sound to ensure a zero resistance connection. A good test for the circuit, assuming there is continuity, is to apply a 1.5 volt DC supply. If it will not run then there is either a high resistance connection in the circuit OR the magnet has lost its original level of magnetism. Check every connection for security and cleanliness. Still won’t run on 1.5 volts?? Apply 9 volts. If it now runs the circuit is OK however the magnet strength is to be questioned. The sliding silver pin and fork must be spotlessly clean with no trace of oil contamination. These contact surfaces can be burnished. Because there is a very small current flowing there is very little sparking at the contacts to cause pitting or erosion. Similarly the rolling silver spring loop and its contact stud must be spotlessly clean. The mechanical components of the movement may be oiled but extreme care must be taken to keep all traces of oil away from electrical connections. When all Else Fails … Remagnetise ! As mentioned before a magnet can and does loose its strength over time due to natural reorientation of the magnetic “domains” in the steel. Demagnetisation may also be due to heat or impact. The Bulle magnet is especially susceptible because of the two opposing North poles at the centre of the magnet. This places the domains in permanent maximum opposition, and with the relatively poor magnetic materials available at the time these clocks were made, de-magnetisation is a matter of “when”, not “if”. A permanent magnet may be revitalised by simply exposing it to a very strong magnetic field. But how does one create the weird Bulle 3-pole magnet? Simply by winding a heavy cloth insulated 1mm copper wire around the magnet as shown below, and applying a brief high current from a supply of about 12 volts DC. The wire must be wound around the magnet exactly as shown, with the wire wound in the direction indicated. Wind a single tight layer of 1mm wire, with no spaces between adjacent turns. Make certain that the winding wire does not make electrical contact with the magnet. Note that this method has been used many times, but strictly speaking is not really recommended. Should the lead manage to weld itself to the battery terminal, a massive current will flow – the leads, coil and magnet will become extremely hot. There is a risk of burns, and possible damage to the battery. While a “proper” magnetising circuit can be used, these are beyond the scope of this article, and are very expensive – even to build.
GUSTAV BECKER AND THE 400 DAY CLOCKGustav Becker commenced clock making in 1850, in Freiberg, Silesia on a small inconspicuous scale. His efforts were certainly rewarded as in 1852 he won a gold medal for his designs that brought his reputation to a peak and business boomed. Up until 1880 most of his clocks were of the weight-driven wall clock style but as of this year he introduced spring driven shelf clocks and his catalogues of that period showed over 400 models! In 1885, Gustav Becker died, but such was the reputation of the company and products that business momentum carried on right through until 1926 when GB was absorbed into the Junghans Company, who continued to market clocks under the GB brand until 1935. In 1885, Gustav Becker died, but such was the reputation of the company and products that business momentum carried on right through until 1926 when GB was absorbed into the Junghans Company, who continued to market clocks under the GB brand until 1935. Gustav Becker is what might be called a “quiet achiever” as there is substantiated evidence that he developed a 400-day clock and tried to commercialise it as early as 1875. This clock had a cylinder escapement with a disc pendulum and is known to have been produced in small numbers up until 1901. Since this design pre-dates the German patent system it was not patented. This GB design became the standard and basis upon which the 400-day clock developments from 1880 were founded. The similarities are easily seen in the picture above. The patent for a torsion pendulum and escapement was issued to Lorenz Jehlin in 1877 and it passed to Anton Harder in 1880. Harder initiated development work on a clock based on this patent and used several existing clock-makers to perform this work. GB was one of these and from 1880 to 1882 and their clock contained a cylinder escapement and/or a crown wheel and verge escapement. These were expensive to make and were not energy efficient in a clock of such a long duration. Harder did not accept this prototype and passed the development work over to Schatz and Wintermantel who found success through the adaptation of the Graham Deadbeat escapement.This ended the input by GB but ultimately, when Schatz and Wintermantel released the first commercial 400-day clocks for sale in 1882, apart from the deadbeat escapement, everything else was of the GB design ! Despite this Anton Harder was able to obtain a very specific patent over the design.There is no recorded acknowledgement of the use of the GB design nor of any dispute by GB! Was there some some sort of “gentleman’s agreement” here? In 1877 the Harder patent ( now under the control of deGruyter ) lapsed thus allowing other clock-makers to commence production. Many did and copied the Jahresuhrenfabrik clock exactly. Gustav Becker Co. took their time and commenced production of a Harder patent 400-day clock in 1902. Ever since they started clock production GB had put serial numbers on their clocks and this continued with the 400-day clocks. The serial numbers that were applied to the earliest production 400-day clocks are around 1,632,650 Every clock made by GB had a serial number stamped onto the back plate. The following is a year / serial number list for dating GB clocks. Considering that Gustav Becker was involved with the early development and prototypes the list starts at 1880. 1880 260,000 1885 500,000 1890 800,000 1892 1,000,000 1900 1,500,000 1913 1,850,000 1923 1,860,000 1925 1,945,399 1926 2,244,868 1927 Restart at 0001 due to take-over by Junghans. GB commenced production with a disc pendulum and introduced a 4-ball design in 1915, however GB was the only company to supply disc pendulums after WW1, in fact they never stopped supplying disc pendulums ! An excellent review of the GB disc pendulums is in the Torsion Times Vol. V, No.2 , pp 42 – 50. GB was innovative in the continuing development of the 400-day clock. These included : Suspension guard, a flat strip mounted on the back plate. 1908 Unique 4-ball pendulum, 3 similar designs. 1915 Pallet and escapement peep holes, in front and back plates. 1916 Finial crest vertical screws replaced by a tab. 1919 Unique special beat adjusting top suspension bracket. 1921 Lantern pinions. 1926 ( Under Junghans” control ) The quality of the GB 400-day clock was excellent and the company’s reputation survived long after the death of the founder, Gustav, in 1885. Unfortunately he did not live to see the real boom and commercial success of his clock design in the early 20th century. There can be no doubt about the reputation of GB as even today, 100 years later the GB brand clock are held in high esteem. GB concentrated on the standard glass domed model with range extension to the larger bandstand/louvre model, a wall clock, 4-glass regulators in brass and wood, an Empire style, and the only 400-day skeleton clock ever made. Despite what appeared to be a progressive and innovative company GB was absorbed into the Junghans Company in 1926. Junghans continued to produce 400-day clocks to the GB design and marketed under the GB brand until 1932. Thus ended the 30 years of 400-day clock production by Gustav Becker, a man, and his company, who had more to do with the design and production of the 400-day clock than he is given credit for. This may be corrected in the very near future.
SPRINGS… There’s millions of them – Napoleon Hats and their ilk. Can I get 8 days out of them? – NOT YET. Is this a bold, rash prediction that one day I will achieve this humble goal or just folly? My recent attempt is with a Norland, 3-holer. Last was with a Norland 2-holer – still not going the distance (even after re-bushing the barrels!). So I need to go back to first principles, starting with the springs. I consulted my references – the most learned company I can think of – Gazely, deCarle etc. Heard of Robinson? Well here’s some wise words written in 1934 … “By far the greatest number of mechanical clocks derive their motive power from springs. The modern high grade mainspring forms a very reliable and compact power storage component, and when housed in a properly designed barrel, provides an excellent driving unit for a timekeeper”. Unfortunately, there is sometimes the mistaken idea that mainsprings and barrels having plenty of power, and operating energetically under almost all conditions, require little attention, and that, unless there has been a definite failure at this point, nothing more than a lookover is necessary. To hold this view is as fallacious as it would be for an automobile engineer to argue that because the gear box and back axle of a car were in perfect order, the engine needed no attention. It is useless to have a train whose depths and pivots are perfect, and whose escapement or chiming and striking mechanism are correctly adjusted, unless the motive power is efficient. To perform this work and to keep doing it over a long period of years, the spring and barrel must be as mechanically perfect as possible. Only by careful design and construction can the correct result be obtained. The ideal conditions are when the mainspring supplies just enough power to drive the train smoothly and evenly throughout the run. Roughness of construction may be overcome by fitting stronger springs than those theoretically necessary. This is often done in badly made clocks, but such measures are basically wrong. They impose heavier loads on barrel arbors, pivots, teeth and clickwork, for no better purpose than to make good errors and rough workmanship elsewhere. The horologist should take pains to see that the springs and barrels of the clocks which pass through his hands are in such order as to give their best performance. Springs for replacements should be of the highest quality, and of the same height and strength as those originally in the barrel. Nor should fracture alone be the reason for replacement. Few horologists seem to renew a spring for any other reason than its breakage, but it should not be forgotten that springs can fatigue, after years, and that this will result in a serious loss of power. The mainspring is perhaps the most severely used spring in the whole of mechanical engineering practice. The service demanded of it is extremely arduous, so that even the best mainsprings lose something of their elasticity under continual use. A spring of the best quality, and of correct height and thickness, will retain its elasticity for a very long period, but even a good spring of wrong size will have a short lived efficiency, and will fatigue or fracture in a comparatively little while. More than this, with such a spring the regulation of a clock to anything like proper timekeeping is impossible. (Doesn’t this make the absolute sense, even today 70 years on?) deCarle describes how to select a new spring … “When selecting a new spring, there are one or two points to consider. The maximum number of turns are obtained if the diameter of the barrel arbor is one third of that of the interior of the barrel and the mainspring occupies one third with one third space. If this condition is observed the outer coil of the spring when fully wound will occupy the position of the inner coil when the spring is run down. The number of turns the barrel will make equals the difference between the number of coils when fully wound up and run down. For instance, if there are 15 coils when run down and 25 when fully wound up round the arbor, the barrel will make 10 turns : 25 – 15 = 10.” But the best guide in my opinion is Conover, “Another problem mainspring which should be replaced is a “tired” or weak spring”. It is difficult to define exactly what is meant by these terms, however … The mainspring on the left is an old one removed from a barrel. The mainspring on the right is new. The old mainspring on the left has a much reduced capability, as shown by the fact that when fully released it is not much larger in diameter than a barrel. In contrast, the spring on the right is new and has never been in a barrel before. It expands to a large diameter. This is not to say that good springs will always look like this one when they are removed from barrels for cleaning and inspection. I have verified that a new spring will be somewhere between the extremes shown in the figure if it is removed from the clock after a test period. Experience will teach you to recognise which springs are weak and which ones are not. One of the most pointed lessons is learned by cleaning and reusing an old spring which looks questionable, only to have it run a clock for six days instead of eight. The entire movement may have to be dismantled to permit the replacement of the spring with a new one. Some repairers replace almost every mainspring in the clocks they repair. Although that is not my policy, I can understand why some people approach mainsprings that way. Ordering a Hole End Mainspring Selecting a replacement barreled mainspring is sometimes as easy as measuring the old one. As a convenience for repairers, most supply catalogs list mainspring dimensions in English and metric units. I prefer to use a micrometer to measure the thickness and a rule to measure the width in millimeters. Thickness of a mainspring must be correct within close limits. A mainspring of 0.3mm thickness is a relatively weak spring, the type used in small French movements. By increasing the thickness by just 0.15mm, we arrive at the powerful springs used in much larger movements. Thickness becomes a compromise when you cannot find the exact mainspring you need in suppliers’ catalogs. My approach is to avoid using a stronger mainspring than the one which came out of the clock unless I know it was too weak a spring. A spring of 0.45mm thickness can wear out the gears in an old movement if the correct spring was 0.4mm. Backing up this general approach is the idea that today’s mainsprings have more torque than 100 year old mainsprings of equal thickness had when they were new. Width of a mainspring is a little less critical than thickness. If the only available mainspring of the correct thickness and length is 1 mm narrower than the original spring, this does not usually present a problem. A wider mainspring cannot be used because it will not allow the barrel cover to fit securely, and in addition, there will be no endshake, or freedom, in the fit of the barrel arbor. Length of an old mainspring can be measured directly if you try to stretch it out, although there is some estimating involved because of the tight inner coils. You can also measure the inner diameter of the barrel and compare it to the “diameter” figure included in suppliers’ mainspring tables. This figure represents the coiled diameter of the wire bound mainsprings as they are shipped to you. If the coiled diameter fits in your barrel, it is close to the correct length. It is far better to use the formula below to find the correct length mainspring for your barrel. This gives you an exact length for the spring of your chosen thickness that will turn the barrel the maximum number of times. This is an important concept because a mainspring which is too short will obviously give a reduced number of barrel turns. It is equally true that a mainspring which is too long will not give the maximum number of possible turns because it fills up some of the empty space in the barrel required for winding and unwinding. The formula is based on the idea that a mainspring occupies only a part of the available space in the barrel. For a barrel to be able to deliver the maximum number of turns possible with a mainspring of a specified thickness, the spring should occupy one half the available area. Mainspring Length in Five Steps Inside diameter of barrel, squared, times 0.7854 Diameter of arbor, squared, times 0.7854 Subtract step #2 from step # 1 Divide by 2 Divide by the mainspring thickness OK, lets try this out on the chiming barrel of the Norland … Barrel ID 47.4 mm, step 1 = 47.4 X 47.4 X 0.7854 = 1764 Arbor OD 17.5 mm, step 2 = 17.5 X 17.5 X 0.7854 = 240 Step 3 1764 – 240 = 1524 Step 4, divide by 2 = 1524 / 2 = 762 Now the mainspring thickness of the original spring = 0.45 mm Hence spring length = 762 / 0.45 = 1693 mm The replacement spring I bought was 0.44 mm Therefore spring length in this case = 762 / 0.44 = 1732 mm, just under the length of the spring I purchased. Not so simple. The number of turns to wind up the barrel was 4 1/4 from dead flat to full wind. Counting the chime strokes gave me 36 hours of Westminster chiming per revolution of the barrel. So 4 turns of the barrel = 144 hours of chiming. Well by my count there are 192 hours in the week. So even if the calcs for the spring are right, the chiming won’t last a week. Is the spring that was in there the wrong thickness? Did I just blindly accept it as being the original? Is this clock chiming restricted to a lot less than 8 days, based on the chime/silent facility hence won’t be bonging away during the night? (this is my guess). Will a thinner spring be powerful enough (= 0.44 X 144 / 192 = 0.33)? This spring has to make many chiming rounds – will it have the guts?