Hello respectable members:

I've decided to post some pictures of the stages of a standard service with Omega Forums very own Stefan.

Here are the service stages of my Stainless Arrowhead Constellation Cal. 505. 2852-9SC : serial 16103235





Crystal had split and had been glued so needed replacing







Broken setting lever needed sourcing too.















Movement overall was in excellent shape, here are some stats. T

he X is average rate of -1.3 sec per day but can put it a bit up so it will gain ca 3-5 seconds per day.​

 

Since the service an new crystal has been sourced and I have ordered a new replacement crown from Cousins UK.
I asked Stefan to just clean the case as I wanted to keep it as original as possible, he was very communicative and helpful!
































Stefan has done a sterling job and I can't wait to receive the watch, it's a real beauty Now, next I will post some of the bumper!





Replacement crown has arrived

Updated Pictures



















I cannot sing Stefans praises enough, it's looking lovely, and still original as it was found (except crown, crystal of course.) Very happy!

 

Nice job!

That's not an escape wheel - it's a click of some sort, maybe to do with the calendar?

 

Sorry, I meant setting lever...

 

Broken setting lever spring

 

Back to "What's in the Guts of a movement 101" for you!

Oh, and BTW, lovely Connie

 

Great job as well. Its always nice to know there's another safe pair of hands for our watches....

 

Rookie mistake! and thanks!

 

Don't sweat the terminology mate - this part has many names depending on where you are in the world, and what era you are from in terms of watchmaking education. This part is commonly called Set bridge, Setting lever spring, or setting lever jumper. If I'm discussing the setting parts with another watchmaker, I often have to tailor the terms I use based on the age of the watchmaker I'm communicating with....clutch lever or yoke, clutch or sliding pinion, etc. It can get confusing even for those who work in the profession.

The movement is in great shape, and although the balance amplitudes are low the timing results are quite good with the Delta at 8 seconds. And I love the lugs on that case too! Enjoy!

Cheers, Al

 

Thanks Al,

I'm glad to know that even the proffessionals get confused from time to time! its like another language, I hope to one day speak!

I have some pictures of a constellation bumper that I haven't even seen working, which needs an escape wheel. Can't wait to see that up and running, but alas, the part is tricky to source! The movement generally seems to be excellent on that one too.

Sorry to sound stupid but what effects the balance amplitudes? and can they be easily adjusted?

Cheers,

Al

 

In this case (after a service by a professional) it could be a weak mainspring

 

Just to be clear, I am not criticizing anyone's work here - some watches are very difficult to get what most would consider decent balance amplitude from. The 470 based Omega movements (like the one above) and even the 550 based watches that so many here love, are typically movements that do not have really "good" balance amplitudes. So full wind horizontal position I would want 280 or more from say a modern 1120, where here I would be happy with 250's. Seiko movements (not that I service many but I have done a few) are also known for not having great balance amplitudes - it's just the way the movement is made. Considering this Cal. 505 movement is allowed to have a Delta of 40 seconds at full wind, measured over only 3 positions, and this one has a Delta of just 8 seconds over 6 positions, means it has been adjusted very well for timekeeping. Parts are also getting pretty scarce for these movements, so sometimes it's just not possible to get amplitudes within specs without replacing a whack of parts, and that is not always easy and is expensive.

So having said that...

Balance amplitude is a measure of how many degrees of rotation the balance wheel makes. For timing machines this is a calculated value based on some sounds that the escapement measures, plus the lift angle value, which is given by the manufacturer and you have to match that value on your timing machine to get accurate amplitude readings. The lift angle for the 505 is 49 degrees, and the machine above appears to be set to 52 degrees (the default setting on most machines) so the amplitude readings are actually a bit lower than what is displayed there. Rule of thumb I was taught in school was that for every 1 degree off your lift angle is, it will change the amplitude readings about 6 degrees.

Some watch companies have upper and lower limits on amplitude. The upper limit is usually measured at full wind, and the lower is measured at full wind -24 hours. The upper limit is there to help prevent knocking, where there is too much balance amplitude, and the roller jewel comes around too far and hits the outside of the pallet fork horn, and rebounds - this causes a very fast rate. Some call this "overbanking" but again this term means different thing depending on where you are in the world. It can also be called "galloping" as it sounds like a horse galloping, and not the regular tick-tock sound. This can be as difficult to solve as low amplitudes are to be honest.

Omega tends to have only a lower amplitude limit, and for the Cal. 505 that is 180 degrees minimum at full wind -24 hours. So to test this you either have to wind the watch fully and let it run for 24 hours before doing the test, or wind it fully and let the mainspring down the equivalent of 24 hours run time. Then in any position you measure the amplitude should be more than 180 - lowest values will be in the vertical positions as there is more friction there than dial up or down. Assuming the numbers above were taken at full wind, then you can't really say if they are lower than Omega specs, but I feel they would be once you correct for lift angle and let the watch run for 24 hours.

This can cause issues with isochronism, and as the watch runs down the timekeeping will vary more than you see at full wind. Problems with posie can be magnified when the watch goes below a certain amplitude, and fast/slow values associated with posie can flip on you - due to the physics involved in how the balance wheel works - we use this to our advantage when dynamic poising, but generally you don't want this happening when the watch is being worn as it makes your timing results more unpredictable.

There really isn't an "adjustment" to be made to fix this (I wish there was!). Balance amplitude is a result of many factors in the watch, so for example you could have dirt in the jewels or bushings, weak mainspring as was noted, wear on pivots causing tipping of wheels, worn balance pivots, too much lock on the pallet jewels, etc, etc....

Hope this helps explain things a bit - these issues can get pretty complicated so I have tried to give you some of the basics here.

Cheers, Al