A mechanical watch needs maintenance because it works. The only open question is how often, and that answer has changed more over the last hundred years than the watch itself. A century ago a good watch went to the watchmaker about once a year; today major manufacturers name about ten years. The reason is a drop of oil.
Why did John Harrison build clocks of wood?
Harrison, who later solved the longitude problem, started out as a carpenter. His early clocks were largely made of wood, and that was no makeshift. The horological historian Andrew King calls the elimination of lubrication the bedrock of his life's work. In a reconstruction of his 1726 regulator at Greenwich, brass pivots run in bearings of lignum vitae, a tropical hardwood that lubricates itself with its natural oil.
There was a practical reason: the oils of his day turned viscous in unfavourable conditions and disturbed the rate. Harrison sidestepped the problem. Royal Museums Greenwich likewise credits his sea clocks with running without lubrication thanks to extensive anti-friction devices. This cannot be carried over to a wristwatch: wooden bearings and rollers need room that a thirty-millimetre movement does not have.
How often should a mechanical watch be serviced?
That depends first of all on the oil. For a long time watchmakers lubricated with animal fats: neatsfoot oil from cattle, or oil from the jaw and head of porpoises, which the watchmaker Ezra Kelley sold in New Bedford from 1844. Such oils oxidise in air into a sticky, sometimes acidic gum. The intervals were correspondingly short: in 1929 a care booklet from Gruen advised cleaning and oiling pocket watches every 12 to 18 months, and wristwatches every six to twelve months.
Then the material changed. In the early 1960s the American manufacturer Nye began moving from porpoise oil and petroleum products to synthetic lubricants. These gum up and age far less. Added to that came cases that keep dust out better, and epilame, surface treatments that hold the drop of oil in place.
Today Patek Philippe recommends servicing every eight to ten years, Rolex about every ten, depending on model and use. In 2007 the British Horological Institute named as normal intervals about five years for watches, five to eight for carriage clocks and ten to twelve for longcase clocks. No single number fits every timepiece: manufacturer guidance, calibre, condition, case and use all play a part. But yearly oiling does not describe the watch. It describes the oil of the time.
Why does a watch keep running when the oil is finished?
A long interval is no free pass, however, and good oil is precisely what makes this hard to see. According to the British Horological Institute, modern synthetic oils let a mechanism run for very long periods even after the oil has lost its oiliness. Gruen already warned that a strong mainspring will keep a watch going even when no oil remains and the pivot bearings are being scored. Then there is dust, which clings to the oil and turns with it into a grinding paste.
Wear follows movement and load, not the calendar: in simple experiments in 1953, John Archard found material loss that grows with sliding distance and load. That is a model, not a law for every movement, but a wristwatch at 28,800 half-oscillations an hour reaches about 250 million a year. That it still runs therefore proves little. More revealing are rate and amplitude on the timing machine and a look inside the open movement.
So what does maintenance preserve?
Harrison's question is not settled even now. In 2001 Ulysse Nardin used silicon escape wheels in its Freak model that need no lubrication, and many manufacturers now work with the material. The rest of the movement still needs its drop. Maintenance remains; only its rhythm has shifted.
It does not stop time but redirects it. Cleaned and freshly oiled, a movement lets time wear on what can be replaced: on the oil instead of the pivot, on a gasket instead of a tooth someone filed by hand two hundred years ago. Stephen Graham and Nigel Thrift call maintenance and repair a missing link in social theory, because they are usually overlooked. With a watch the reason is simple: successful maintenance leaves no event behind, only one more day on which the watch tells the right time. A watch does not reach the next generation only because it was well built, but because someone looked after it.
Sources
Andrew King, The Origins of John Harrison's 'Pendulum-Clock' Technology, in Rory McEvoy and Jonathan Betts (eds), Harrison Decoded, Oxford University Press (2020)
Royal Museums Greenwich, Longcase clock, ZBA0020, reconstruction of the 1726 Harrison regulator
Royal Museums Greenwich, John Harrison's Marine Timekeepers
Wikipedia, John Harrison and Lignum vitae
Nye Lubricants, 175 Years of History, company history
Gruen Watch Makers Guild, How to Select and Care for a Fine Watch, booklet (1929)
British Horological Institute, The Practical Lubrication of Clocks and Watches (2007)
Patek Philippe, Watch Care Recommendations
Rolex, Caring for your Rolex: Frequently Asked Questions
J. F. Archard, Contact and Rubbing of Flat Surfaces, Journal of Applied Physics 24 (1953)
Phillips, Ulysse Nardin, Freak, catalogue essay
Stephen Graham and Nigel Thrift, Out of Order: Understanding Repair and Maintenance, Theory, Culture & Society 24 (2007)