Blog: Cylinder Escapements

Date: 5 October 2015

I make additions and corrections to this web site frequently, but because they are buried somewhere on one of the pages the changes are not very noticeable, so I decided to create this blog section to highlight new material. Here below you will find part of one of the pages that I have either changed or added to significantly.

The section below about cylinder escapements is from my page about watch movements.

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Cylinder Escapement

The cylinder escapement was invented in England by Thomas Tompion and others in around 1695, and perfected after Tompion's death by George Graham, one of Tompion's apprentices. The cylinder escapement was never widely embraced by English watchmakers.

The Swiss in contrast perfected the design of the cylinder escapement and produced millions of watches with it, right up to the beginning of the twentieth century. Although they gave good service to millions of customers, Swiss watches with cylinder escapements that were imported into England were usually at the cheaper end of the price scale and consequently the cylinder escapement is usually looked upon rather contemptuously by watch collectors.

The cylinder escapement is capable of good timekeeping, although it is more susceptible to variations caused by external disturbances than the lever escapement, but it needs very regular servicing, which is becoming more and more difficult as time goes on. There is nothing particularly difficult about servicing a cylinder escapement, but because they have not been made since the nineteenth century many watch repairers do not have any experience of them and try to avoid working on them.

Swiss cylinder escapements are often found in watches with Lépine calibres. This type of movement is named after Jean Antoine Lépine, a French watchmaker who created the modern slim form of watch with separate cocks and bridges in the eighteenth century.

The cylinder is always in contact with the escape wheel, causing sliding friction as the balance and cylinder turn. Without regular cleaning and oiling this will cause severe wear to the cylinder. Today it is expensive to replace a worn or broken cylinder and the number of repairers who can replace a cylinder is small and dwindling.

The cylinder escapement is also called the horizontal escapement, in contrast to the vertical verge escapement that preceded it.

Cylinder escapement from Saunier

The image here is based on an image in Saunier's Treatise on Modern Horology. Fig. 1 on the left shows why the cylinder escapement is so called, a cylinder with its wall partly cut away forms the arbor on which the balance turns, the two plugs at the top and bottom carry the pivots. The cut away part of the cylinder wall allows the shaped teeth of the escape wheel to pass as the balance swings. The wider cut away at the bottom allows the tooth support to pass.

The plan view Fig. 2 shows how the escapement works. The figure shows a series of actions by showing the cylinder in white adjacent to successive teeth of the escape wheel; in reality of course the cylinder turns back and forth in one place while the escape wheel ticks round. The different steps are labelled with red numbers.

At step 1 the balance is turning clockwise and the lip of the cut out in the cylinder is being pushed by the inclined face of an escape wheel tooth. This push on the cylinder gives energy to the balance to keep it swinging. Step 2 shows the same tooth locked against the inside of the cylinder. Step 3 shows how the tooth remains locked as the balance swings to its full amplitude, and then in step 4 the balance begins its swing back anticlockwise. In step 5 the tooth begins its escape from the cylinder. Step 6 shows how the inclined face of the escaping tooth gives a push to the cylinder in the opposite direction to step 1, again giving energy to the balance to keep it swinging.

Step 7 shows the next tooth on the escape wheel dropping onto the outside of the cylinder. It remains locked by the outside of the cylinder as the balance continues its swing anticlockwise. When the balance has swung fully anticlockwise it swings back again and step 1 repeats.

Because a tooth is always in contact with the cylinder this is called a “frictional rest” escapement. This friction is part of the reason why the balance needs to constantly be given more energy to keep it swinging. More friction occurs at the cylinder pivots, and due to air resistance as the cylinder swings.

The sequence of steps shows another limitation of the cylinder escapement, the amplitude is limited because the tooth must lock on both the outside and inside of the cylinder, so the amplitude cannot be more than 180°.

The amplitude of the balance determines the maximum rotational velocity or rim speed that the balance achieves, and therefore affects the amount of energy stored in the oscillating balance, which is propotional to the square of rotational velocity. A detached lever escapement can reach amplitudes of over 270° and therefore store a great deal more energy than the balance of a cylinder escapment, making it more resistant to disturbances.

Cylinder Wear

It is often said that a cylinder escapement cannot keep good time, but Saunier explains that once optimum proportions and materials had been arrived at after some years of development in Switzerland, a watch with a cylinder escapement and without a fusee could be a better timekeeper than a watch with a verge movement and fusee. However, this is rather a case of damning with faint praise, because a cylinder escapement is capable of very good performance if it is in good condition, that is without wear, clean and with fresh oil.

In "Watchmaking in England, 1760-1820" by Leonard Weiss is the following quote from 'A Mechanic' in 1859, which throws an interesting light on the situation:

"The horizontal escapement was invented in England, and was found by its frictional action during the state of rest of the train so nearly to counter-balance the variable impulse given by the spring, that even with the crude going–barrels the average performance of the watch was amazingly improved. English engineers had by experiment proved that friction was much less between different metals than between similar, therefore the watchmaker made the horizontal wheel of brass and his cylinder of steel. Meanwhile public taste demanded flat watches, and the Swiss made the horizontal escapement of steel entirely, thereby sacrificing theory to demand. After a time it was found that, whereas the brass wheel destroyed the cylinder very quickly, the steel wheel hardly marked it in years of wear, clearly showing that even if there be a slight excess of that friction that retards motion, it is a less evil than the absolute wear of the machine itself. The Swiss were thus rewarded for studying the taste of the public by a large trade, and have made their country the home of the horizontal escapement."

The major problem with the brass escape wheel and steel cylinder combination used by English watchmakers was that the softer brass picked up particles of dust which embedded themselves into the surface of the escape wheel, turning it into a grinding wheel as it rubbed against the steel cylinder, thus wearing it away very quickly. The Swiss combination of steel wheel and steel cylinder didn't suffer nearly so much from this problem, although dust in the oil will still cause wear over the years.

The point that 'A Mechanic' is making is that because the cylinder escapement is a "frictional rest" escapement it should, in theory, be improved by reducing friction and therefore using a combination of brass and steel for the wheel and cylinder. However, in practice the friction of the cylinder is actually beneficial to timekeeping, because in a movement without a fusee, where the spring barrel called a "going barrel" drives the train directly, the friction evens out the torque from the mainspring.

The feature of the cylinder escapement that caused so much objection to English watchmakers is that the escape wheel is always held in contact with some part or other of the cylinder. The force of the main spring presses the escape wheel against the cylinder causing friction. But this objectionable friction is also the secret of the unexpectedly good timekeeping of the cylinder escapement. When the main spring is fully or near fully wound and the force it exerts is at it highest, the friction in the escapement is also at its highest. As the main spring runs down it produces less force and the friction in the escapement decreases.

The combination of high friction with high spring torque, and low friction with low spring torque, results in a greater consistency of amplitude of the balance from when the mainspring is fully wound to when it is run down. If the balance and spring were perfectly isochronous this wouldn't matter because the period in big and small amplitudes would be the same, but perfection is difficult to achieve, especially with eighteenth and nineteenth spring technology, and the greater consistency of amplitudes resulted in a rate that was more constant than might have been expected. The combination of steel on steel used by the Swiss produced a superior timekeeping performance to the lower friction combination of brass on steel favoured by the English watchmakers for theoretical reasons.

English watchmakers couldn't get over their view that using steel on steel was bad engineering, so when they did make cylinder escapements they used brass escape wheels and then, observing that these wore out quickly, condemned the cylinder escapement. The Swiss however were not so purist and observing that steel on steel worked very well, even if it shouldn't in theory, made millions of watches with cylinder escapements, which they sold cheaply to customers who didn't know or care about the difference between a cylinder and a lever escapement and were happy to get a cheap watch that kept time well. And we all know what happened to the Swiss and the English watch making industries.

Identification and Care of a Cylinder Escapement

An early Stauffer movement with cylinder escapement. Such movements are usually anonymous. Click image to enlarge.

How can you tell if a watch has a cylinder rather than a lever escapement? The picture here is of an old movement with cylinder escapement. This is a mid nineteenth century movement and later movements may look different, but their wheel trains are the same so ignore the shapes of the cocks and bridges and concentrate on the wheels.

Start at the pivot of the centre wheel, the one right in the middle of the movement, then identify the pivots of the third and fourth wheels. The next wheel in the train is the escape wheel, and in this movement the pivot for the escape wheel arbor is underneath the balance – the red arrow labelled "escape" is not pointing to the balance but to the grey steel escape wheel that is below the balance.

The teeth on the escape wheel engage directly with the cylinder, which is part of the balance staff. There is no lever between the escape wheel and the balance staff as there is in a lever escapement, so the escape wheel of a cylinder escapement has to be planted right next to the balance staff. The escape wheel of a cylinder escapement also has its teeth shaped like those shown in the diagram from Saunier above.

Although the performance and longevity of Swiss made cylinder escapements with steel escape wheels and steel cylinders was better than English ones with brass escape wheels and steel cylinders, the difference is relative rather than absolute; the cylinder wears more slowly with the Swiss steel escape wheel, but it still does wear as the oil picks up dust and turns to a fine grinding paste. They were also usually at the lower end of the price scale so the train pivots are not jewelled. Jewels in watch movements are not just there to look pretty, or even to reduce friction; their principal role is to provide a hard bearing surface the reduces wear. An watch without train jewels needs servicing more than one with jewels if wear of the bearings in the plates is going to be kept within acceptable limits.

The only way to delay the inevitable is to have the movement regularly serviced, when it will be cleaned to remove the old mixture of oil and dust and lubricated with fresh clean oil. This should be done before the performance starts to deteriorate noticeably, because by then the damage can have been done, and replacing a cylinder is a job that fewer and fewer watch repairers are prepared to do. Even if you can find someone who will take on the task, it may be uneconomic because, in the main, watches with cylinder movements are not very collectible and therefore not highly valued - although if the item is a family heirloom this shouldn't matter.

The first watchmaker to make great use of the cylinder escapement was Jean Antoine Lépine who used them in watches that were, at the time, sensationally thin. With his designs Lépine created the modern watch and deserves to be far better known than he is. Lépine's designs formed the basis for the vast majority of French and Swiss watch production in the late eighteenth and through the nineteenth century. There is some information about dating Lépine calibres on the page about Jean Antoine Lépine.

The great Abraham Louis Breguet overcame the problem of wear in the cylinder escapement to a very great extent by making his cylinders of ruby, but don't expect to find such an exotic device in a cheap Swiss watch.