A mechanical watch is powered by an internal spiral mainspring which turns the gears that move the hands. The spring loses energy as the watch runs, so in a manual watch movement the spring must be wound periodically by turning the crown, to provide energy to run the watch.
A self-winding watch movement has a mechanism which winds the mainspring. The watch contains an oscillating weight (the rotor), which turns on a pivot. The normal movements of the user’s arm cause the rotor to pivot on its staff, which is attached to the winding mechanism. The motion of the wearer’s arm is translated into circular motion of the rotor which, through a series of reverser and reducing gears, winds the mainspring. There are many different designs for modern self-winding mechanisms. Some designs allow winding of the watch to take place while the rotor swings in only one direction while other, more advanced, mechanisms have two ratchets and wind the mainspring during both clockwise and counterclockwise rotor motions.
Rolex Reverser Gears
The fully wound mainspring in a typical watch can store enough energy reserve for roughly 1 day, allowing the watch to keep running through the night while stationary. In many cases automatic watches can also be wound manually by turning the crown, so the watch can be kept running when not worn, and in case the wearer’s wrist motions are not sufficient to keep it wound automatically.
Automatic Mainspring
Self-winding mechanisms continue working even after the mainspring is fully wound up. If a simple mainspring was used, this would put excessive tension on the mainspring. This could break the mainspring, and even if it did not, it would damage the movement.To prevent this, a slipping clutch device is used on the mainspring so it cannot be overwound.
In the slipping barrel, the mainspring is attached to a circular steel expansion spring, often called the ‘bridle’, which presses against the inside wall of the barrel, which has serrations or notches to hold it.
Mainspring barrel showing bridle
As long as the mainspring is less than fully wound, the bridle holds the mainspring by friction to the barrel wall, allowing the mainspring to be wound. When the mainspring reaches full wind, its force is stronger than the bridle spring, and further winding pulls the bridle loose from the notches and it simply slides along the wall, preventing the mainspring from being wound further. The bridle must grip the barrel wall with just the right force to allow the mainspring to wind fully but not overwind. If it grips too loosely, the bridle will begin to slip before the mainspring is fully wound, a defect known as ‘mainspring creep’ which results in a shortened reserve power time.
You may experience that your self-winding watch occasionally stops overnight or appears to be running slowly. This does not necessarily indicate a malfunction or defect in the watch. In most cases, the problem is related to the power reserve that has not been properly initiated or, may be the result of too insufficient wrist action while wearing the watch.
For a self-winding watch to function properly, the mainspring must build up a sufficient power reserve. Many people are unaware that a self-winding watch needs to be wound first manually before it will run automatically. This is called the initiation process. Without the initiation process, the watch will never operate properly or consistently.
To initiate the power reserve, the watch must be wound manually. Turn the winding crown at the 3 o’clock position, in a clockwise direction for about 40 revolutions. This start up wind is usually sufficient for most automatic watches.
After completion of the initiation process, the watch will wind itself automatically (rebuilding the power reserve) by means of an oscillation weight that shifts every time the watch’s position is changed by the action of the arm and wrist.
180 degree bumper automatics
Omega Automatic and reverser gears
ETA Automatics #2824 and #2892
Bulova Automatics
Seiko Automatic
A self-winding watch should be worn at least eight hours a day to maximize the power reserve and the wearer should remain active. If this is not possible, or if the watch has been off the wrist for more than 15-20 hours, the initiation process must be repeated.
22 Comments
chuck
Love reading your blog keep up the good work
Mark Morgan
Great information. I never knew about the initiation process. This tells why my rolex acts funny when I get it out of storage. thanks Mark
George
Very interesting information! I always enjoy the technical aspects of your newsletters. Thanks!
Bill Lees
Hi Mark, Just before Christmas you overhauled my son’s Rolex. Ever since we gave him the the watch in 1985,it has never kept good time and it has had a broken rotor shaft 3x. He was not a believer in Rolex. Since you worked on his watch, it now keeps perfect time. Since Dec. 25, he compares the time against his i-phone an it is within 2-3 sec. He is really impressed with your work. He is a Rolex lover for the first time and that makes his mom and I feel very good. We bought the watch in Zurich, Switzerland. Thanks
Justin
Thank you for the great blog post. I now understand how my automatic watch stays wound!
Tony
I have a Seiko automatic divers watch and also a Watch winder box And the box spins counterclockwise only I was wondering if this will damage my watch?
Phil
Seiko’s automatics dont have manual winding
DANIEL Gagliano
That’s an excellent explanation, Tx!
John Titcombe
Hi Mark,When I received my rolex from your repair shop,I did as you suggested and wound it 35 times.I also learned how to get the stem to lie flat once I changed the DayDate mechanism.Thank you for tricks of the trade-FREE! HeeHee.Johnny.
Mark Morgan
The news letters keep getting better. Will be looking forward to the next one.
Mark
Bob Hursh
As always, nothing like getting an explanation from an expert!
Manh Pham
This is the job of a watch doctor. He can answer all kinds of questions from simple ones to very hard ones. I do not know how long it takes for a watch doctor to graduate, but I think besides the amount of time required for his graduation, experience and adroitness are also of importance as well. There are doctors everywhere, but good doctors are just a few. Thank you, Mark. I am waiting for your informative blogs as ever!
Herbert Weatherly
Thank you for the explanation of how the self winding works. I like to understand these things
Herb
Susan
This information has been so helpful for me. I purchased my first automatic watch and reading your post explains so much about initiating the watch to begin with so that it will keep time for 24 hours as long as I wear it daily for at least 8 hours. Thanks again.
Dennis N
I have a new Seiko automatic watch. I don’t wear it all the time. Can I put it on my watch winder? If so what direction and speed do I use? Thanks for your great blog keep up the good work
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James Fowler
I have a Seiko 5626B. When you wind it and release the crown, the auto winding weight will unwind the movement. It goes round and round until the watch is unwound. Any idea of the problem and advice is appreciated.
Tim
Great automatic watch guide! A question: What is your opinions about watch winders? I have heard both good and bad things about them. Some says they can prolong the life of a watch while others say they are a waste of money.
Wristerr
Some people come into our lives and leave footprints on our hearts, while others come into our lives and make us wanna leave footprints on their face.
Oliver Smith
I am grateful to you for answers to some of my questions)
David J
I’ve just received my watch back from Mark I did what he told on the instructions that he gave and it works as it should do again it’s running very good again from the overhaul that he did I’ll recommend Mark and his shop to whoever owns a Rolex watch.
Tim Larson
Very nice automatic watch guide! A quick question: What do you think about watch winders? I heard mixed reviews about them. Thanks Tim.