Dr. Ito's In-Depth Analysis of Mechanical Watches! Vol. 42 - What is "Underwinding" in an Automatic Watch?

Hello everyone!

This column discusses mechanical watches from an engineer's perspective. For the 42nd installment, we will be talking about:

"What is 'insufficient winding' in automatic watches?"

This will be our topic for today.

It's common for people who are new to automatic watches to experience issues such as, "I noticed it was 2-3 minutes slow," or "It stops even though I'm wearing it or it's in a watch winder." We sometimes receive inquiries about such problems, even when the watch was recently purchased and is still under warranty.

Some of you might become anxious and think, "Is this a defective product?" However, in many cases, the cause is "insufficient winding of the mainspring."

Just hearing the name "automatic" might lead some to mistakenly believe that the mainspring winds itself just by wearing the watch, right?

This time, we will explain common issues related to such automatic watches.

What is insufficient winding?

 

"Insufficient winding" in an automatic watch literally refers to a state where the mainspring is not sufficiently wound, primarily leading to malfunctions such as "the watch stopping quickly" or "the time running slow."

You can probably understand why a watch might stop, but why would it run slow? This is largely related to its mechanism.

 

For example, when your smartphone battery is running low, you probably start to panic. However, with digital devices, the computer usually manages things well, and they are designed to be usable until 1% remaining battery.

However, with analog devices like mechanical watches, the power they can deliver varies greatly between a fully wound mainspring and one that is almost unwound.

As the mainspring unwinds, its torque weakens, making it difficult to maintain stable accuracy. This is what causes the watch to run slow. And if there isn't enough winding, it will stop sooner than its actual power reserve.

So, why does insufficient winding occur? You might feel anxious thinking, "It's an automatic, but it stops even when I'm wearing it."

Even when an automatic watch is worn, the mainspring may not wind properly if there isn't enough arm movement or if the wearing time is short.

Watchmaking technology has improved in recent years, significantly increasing winding efficiency. Nevertheless, wearing it for about 8 hours a day is generally considered the benchmark for stable accuracy. If you only wear it during your commute and take it off at the office, or if you primarily do desk work and don't move much, it's possible the watch isn't being wound properly.

Of course, there is also the possibility of a malfunction.

Common issues include the automatic winding mechanism's oil running out, causing the rotor to become heavy and impede winding. Other possibilities include foreign matter such as dirt getting inside, or loose screws preventing the watch from achieving its original winding efficiency.

Why automatic watches still need manual winding

If you don't wear your watch for long periods, or if it often runs slow or stops, you should definitely try winding the mainspring using the crown. Most mechanical watches can be fully wound by manually turning the crown about 40 to 60 times.

When starting a watch that has stopped, it's recommended to manually wind it about 20 to 30 times (roughly half of a full wind) before wearing it.

Important precautions are not to wind it too forcefully and not to overwind it.

Manual-winding watches always have a "winding stop," but automatic watches use a rotor to wind, so if a winding stop were provided, even when fully wound, a load would be applied, potentially breaking the mainspring. This is a major reason why manual-winding watches are said not to be overwound.

Therefore, automatic watch mainsprings are equipped with a "slipping attachment."

As shown in the image above, by bifurcating the tip of the mainspring, it doesn't stop even when fully wound, but rather slips to prevent the mainspring from breaking. That's why, when an automatic watch is wound beyond a certain point, you might hear a faint sound of the mainspring slipping.

However, repeatedly allowing it to slip is not advisable. Frequent slipping can put stress on the slipping part and accelerate its degradation. As mentioned earlier, when you use the watch, only wind it gently about 20-30 times.

Summary

What did you think?

If you're ever troubled by issues like, "Huh? My watch is running slow..." or "My watch keeps stopping...", please try gently winding the crown yourself when you use it.

However, if you notice anything unusual, such as "the accuracy is off even when I wind the crown," "there's an unusual noise that wasn't there before," or "the feeling of winding the crown is strange," we strongly recommend consulting the store where you purchased it.

We hope this article has provided useful information and sparked even a little interest in luxury wristwatches! Also, if you have any questions, please feel free to ask us directly, and we will be happy to answer them thoroughly. We look forward to your visit and inquiries.

Look forward to the next time! See you then!