Blog: Cylinder Escapements
Date: 5 October 2015Copyright © David Boettcher 2006 - 2017 all rights reserved.
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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The cylinder escapement (also called the horizontal escapement, in contrast to the vertical verge escapement that preceded it) was invented in England by Thomas Tompion in 1695 and perfected after Tompion's death by George Graham, an apprentice to Tompion. The cylinder escapement was never widely embraced by English watchmakers, and once the English Lever escapement had been perfected in around 1820 the manufacture in England of cylinder escapements ceased completely.
The Swiss in contrast perfected the design of the cylinder escapement and produced watches with it in hundreds of thousands right up to the beginning of the twentieth century. 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, although it is capable of quite good timekeeping. Its major drawback is that without regular cleaning and oiling the cylinder can wear very badly, which today would probably scrap the watch because it would be uneconomic to repair.
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 receiving impulse from the inclined face of an escape wheel tooth as it enters the cylinder. 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 impulse to the cylinder.
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. 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 must be less than 180°. The amplitude determines the maximum speed that the balance can achieve, and therefore affects the amount of stored energy. A detached lever escapement can reach amplitudes of over 270° and therefore store a lot more energy, making it more resistant to disturbances.
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 was a far better timekeeper than a watch with a verge movement and fusee.
In "Watchmaking in England, 1760-1820" by Leonard Weiss I found the following in a 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 point that 'A Mechanic' is making is that because the cylinder escapement is a "frictional rest" escapement it should, in theory, be improved by minimising friction and therefore using a combination of brass and steel for the wheel and cylinder. However, the friction of the cylinder is actually beneficial to timekeeping, because it evened out the torque from the mainspring in a movement with a going barrel, i.e. without a fusee.
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 torque with high friction and low torque with low friction results in a greater consistency of amplitude of the balance between fully wound and nearly 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.
The other problem with the brass wheel and steel cylinder combination used by the 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.
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 happy customers, who didn't know or care about the difference between a cylinder and a lever escapement and were just happy to get a cheap watch that told the time reasonably well. And we all know what happened to the Swiss and the English watch making industries as a result of this difference in attitudes.
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 a movement with cylinder escapement. If you start at the centre pivot, the one right in the middle of the picture, you can then identify the pivots of the third and fourth arbors. 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.
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.
Copyright © David Boettcher 2006 - 2017 all rights reserved. This page updated November 2017. W3CMVS.