Wearing vs non wearing time accuracy

[Old Colonel]

I am a neophyte to understanding mechanical watches but I have observed something and I want to understand it better.

I purchased a 34mm 1953 Oyster Perpetual 6285 w/645 movement off eBay. Once it arrived and I wound it and set it I let it sit on a table, it consistently lost 8-10 minutes a day. Then I took off my explorer and wore the Oyster Perpetual watch for two days, the watch stayed within 20 seconds a day? I know I need to send it for a service but is the difference between a sedentary watch vs a worn watch often so dramatic?

[R.W.T.]

[QUOTE=Old Colonel;10831914]I am a neophyte to understanding mechanical watches but I have observed something and I want to understand it better.

One issue can be the winding is much more incremental with the automatic mechanism than your hand winding. The bridle allows the mainspring to slip so as not to overwind or break the gears. Your hand winding, unless you ease it right to the top before it slips...will cause it to not be at full wind so the amplitude could be so low it's losing time.

When you wore it the automatic portion kept it topped up enough to be accurate. That's why you have to wear these watches to service them. All of the machinery and formulas and all of that are great for a modern (post 15xx series mvt.) watch...but on the old ones...how does it keep time on the wrist? This is the important factor. I wear every single watch of this era to test for a week in order to regulate it and make sure it's running properly on the wrist.

Also if it hasn't run in a while it might have dispersed some lubrication around.

Other factors surely may be in play but this is partially what has occurred possibly.

The thing is too....we must remember that the entire REASON for the automatic winding was not for the convenience of not having to wind the watch but rather to keep the mainspring at constant tension over a longer period of time during the day for accuracy.

There is a principle called isochronism. The mainspring will have more power at the top of the wind than at the bottom. So the degree of swing of the balance will change as the watch winds down during the day. To regulate that one must find the sweet spot. The larger the degree of swing theoretically, the slower the watch will run as it takes longer to complete a cycle of oscillation. As the watch winds down the degree of swing is less so the watch speeds up. So a hand wind watch will give one reading at the beginning of the day and another at the end.

The automatic mechanism keeps the mainspring at a relatively constant tension during the wearing period for more accuracy and ease of regulation. :-)

If the watch is serviced and is still exhibiting this kind of differentiation there is too much position error.

More than likely it is a combination of all of the above.

The watch is likely dry and the upper pivot of the balance and escape wheel in the flat are seeing zero lubrication and it is very sluggish.

I can service the 645 calibre if you need.

[Tools]

External forces on early, slow beat, movements is usually more dramatic than the later fast beat movements. A worn watch is generally faster because the external forces keep the hairspring from completing full oscillations, which take more time to complete. Shorter oscillation (amplitude) equals faster ticks.

Newer movements have stronger mainsprings and more ticks-per-second, so it takes a lot more to change their timing.

I would expect a fresh service and new parts with less tolerance to result in a more accurate daily variance, but don't expect miracles.

[nda]

Originally Posted by Old Colonel

I know I need to send it for a service but is the difference between a sedentary watch vs a worn watch often so dramatic?

Not so dramatic - but it does make a difference.

My new Rolex loses 2 seconds a day - but if it's left dial upwards overnight it speeds up by 2 seconds.

[Dan S]

8-10 minutes per day difference is a bit hard to explain, but I'm not too surprised that the timekeeping is different on and off the wrist. Positional variation alone could explain part of it. I assume your previous "sitting on a table" experiment was dial-up. If you feel like doing more tests, you could time the watch under static conditions using a few more positions: dial-down, crown-up, crown-down.

[R.W.T.]

Originally Posted by nda

Not so dramatic - but it does make a difference.

My new Rolex loses 2 seconds a day - but if it's left dial upwards overnight it speeds up by 2 seconds.

That's totally normal.

This is a completely different world all around.

[R.W.T.]

Originally Posted by Dan S

8-10 minutes per day difference is a bit hard to explain, but I'm not too surprised that the timekeeping is different on and off the wrist. Positional variation alone could explain part of it. I assume your previous "sitting on a table" experiment was dial-up. If you feel like doing more tests, you could time the watch under static conditions using a few more positions: dial-down, crown-up, crown-down.

It's dry. There's no oil in the cap jewel for the balance and escape wheel.

[Dan S]

Originally Posted by R.W.T.

It's dry. There's no oil in the cap jewel for the balance and escape wheel.

Right, thanks, I guess that could explain extreme variation. And further testing is probably not really a great idea.

[R.W.T.]

Originally Posted by Dan S

Right, thanks, I guess that could explain extreme variation. And further testing is probably not really a great idea.

I think in this case we have to assume. You never know til you get in there.

There may be some oil left in the jewels in the round...but there also may be a big dried up piece of wax on the surface of those cap jewels where the oil used to be.

Really without seeing it...impossible to tell.

8 -10 MINUTES in the flat is extreme...and to pick it up and wear it and have it run well...

lots going on.

[1945Datejust]

Old Colonel send the watch to Tommy (R.W.T.) and let him service the movement. He very good with the older movements. He's worked on my 1958 6605 and I couldn't be happier.

[R.W.T.]

Originally Posted by 1945Datejust

Old Colonel send the watch to Tommy (R.W.T.) and let him service the movement. He very good with the older movements. He's worked on my 1958 6605 and I couldn't be happier.

Thanks Andy!

[motoikkyu]

R.W.T. is an absolutely amazing watchmaker! He has done miracles with some of my bubblebacks! Can't say enough good things about him!

[Old Colonel]

Phillip Ridley has two of my watches now. I will await his recommendations on best course of action.

It is great that there are so many good watchmaker options. It helps keep them competitive.