WatchUSeek Watch Forums banner
1 - 7 of 7 Posts

·
Mod. Russian, China Mech.
Joined
·
19,430 Posts
Discussion Starter · #1 ·
Has any expert here ever disassembled a Sea-Gull ST6 alongside a Sea-Gull ST16? Or know of any on-line photo tear-down of such?

The balance wheel seems to be the same on both and I was wondering what other components might match. Just following a hunch to get a better idea of the underlying development process.
 

·
Registered
Joined
·
2,616 Posts
Has any expert here ever disassembled a Sea-Gull ST6 alongside a Sea-Gull ST16? Or know of any on-line photo tear-down of such?

The balance wheel seems to be the same on both and I was wondering what other components might match. Just following a hunch to get a better idea of the underlying development process.
What an awesome question/idea
 

·
Mod. Russian, China Mech.
Joined
·
19,430 Posts
Discussion Starter · #3 ·
What an awesome question/idea
It's just the strange way my brain works.

Recent discussions here about the ST16 and ST17 made me realize that the ST17 appears to be an attempt to 'correct' a particular shortcoming of the ST16; the location of the 4th wheel located at 5 o'clock, rather than at 6 (the natural location for a sub-dial). That got me wondering why they didn't just design it like that in the first place. Obviously the base movement (but not the auto winding) is heavily influenced by the Miyota 8215. So they took a proven design without thinking too much about it. But why that particular design? What is so good about the Miyota that would particularly suit Sea-Gull's needs? Somebody on another forum once stated the view that the Miyota was just an over-grown ladies watch movement; meaning that it used a lot of small parts suited to small movements, but spread out over a mid-size main plate. Aha! I thought; maybe the key to this is that the ST6D was the only automatic that Sea-Gull was set up to produce back in 1997. They wanted something simpler and more robust for man-sized watches without having to retool for a complete new movement.

Unfortunately the only way to test this hypothesis is to dismantle an ST6 and ST16 alongside each other. I lack the knowledge and means to do that, so my idea remains just an idea.
 

·
Registered
Joined
·
8,842 Posts
Theoretically, any movements operating at the same beat rate (21,600 bph in this case) should be able to use any balance/hairspring assembly of any movement operating at the same speed. Simply because the balance/harspring assembly will always vibrate at its set frequency.

The only thing keeping this from being true in reality is the variation in spring stud locations and designs (Breguet, flat, flat with a dog-leg etc), balance staff pivot variations and size restrictions.

Variations in roller table and pallet fork geometry will also influence the energy imparted to the balance, so will have an influence on the speed.

If a movement manufacturer was constantly modifying an existing design (early ETAs are a prime example) the same balance assembly might be used over and over again. However, if the geometry of the movement changes, the the spring and or pallet may have to be changed to fit the required shape. These changes should be fairly easy to spot visually.

If however you are talking about just the balance, not including the spring or roller table, I am sure the two Seagulls use the same balance. ETA's 11-1/2''' movements, throughout the seventies to the present, only had three balance sizes, the Ø 1.1 cm size, the Ø 1.0 cm size and the Ø 0.9 cm size. Ordinarily, the 1.1 cm was used as a 21,600 bph, the 1.0 cm was 28,800 bph, and the 36,000 bph used the 0.9 cm balance. But, with changes to the stiffness of the hairspring, the 0.9 cm balance is used on the 28,800 bph 2892, and the 1.1 cm balance is used on both the 21,600 bph and 28,800 bph 2870 and 2871.
 

·
Mod. Russian, China Mech.
Joined
·
19,430 Posts
Discussion Starter · #5 ·
Theoretically, any movements operating at the same beat rate (21,600 bph in this case) should be able to use any balance/hairspring assembly of any movement operating at the same speed. Simply because the balance/harspring assembly will always vibrate at its set frequency.

The only thing keeping this from being true in reality is the variation in spring stud locations and designs (Breguet, flat, flat with a dog-leg etc), balance staff pivot variations and size restrictions.

Variations in roller table and pallet fork geometry will also influence the energy imparted to the balance, so will have an influence on the speed.

If a movement manufacturer was constantly modifying an existing design (early ETAs are a prime example) the same balance assembly might be used over and over again. However, if the geometry of the movement changes, the the spring and or pallet may have to be changed to fit the required shape. These changes should be fairly easy to spot visually.

If however you are talking about just the balance, not including the spring or roller table, I am sure the two Seagulls use the same balance. ETA's 11-1/2''' movements, throughout the seventies to the present, only had three balance sizes, the Ø 1.1 cm size, the Ø 1.0 cm size and the Ø 0.9 cm size. Ordinarily, the 1.1 cm was used as a 21,600 bph, the 1.0 cm was 28,800 bph, and the 36,000 bph used the 0.9 cm balance. But, with changes to the stiffness of the hairspring, the 0.9 cm balance is used on the 28,800 bph 2892, and the 1.1 cm balance is used on both the 21,600 bph and 28,800 bph 2870 and 2871.
Thanks for that. The pallet lever was one part that I thought might go a long way towards proving my idea one way or the other, because it seems like such a complicated and specific piece compared to the wheels.

Unfortunately Reto at the PMWF seems to have deleted his photo tear-down of the ST6.
 

·
Registered
Joined
·
8,842 Posts
Unfortunately, visual differentiation to pallet forks is almost impossible. I had an ETA 2878 (28,800 bph) and an ETA 2879 (21,600 bph) apart at the same time. I though the non-interchangeable parts would be easy to tell apart. The wheels were, the 2879 escape had more teeth on the pinion, the 2878, the fewer; the 2879 fourth wheel had six spokes, the 2878, eight, the mainspring I figured would be too similar to tell apart so I kept them segregated. I was picking and choosing the best (cosmetic) parts to be build up.

The pallets looked the same. When I put the two back together, one ran about a minute fast, the other a minute slow. That was when I went line by line through the bestfit parts numbers to see exactly which parts where actually the same.

Turns out only five parts are different and the sped changes: mainspring, pallet, fourth wheel, escape whel and the balance assembly (complete, or if you can vibrate a hairspring to match it to the existing balance/staff assy, spring and roller table.)
 

·
Mod. Russian, China Mech.
Joined
·
19,430 Posts
Discussion Starter · #7 ·
Unfortunately, visual differentiation to pallet forks is almost impossible. I had an ETA 2878 (28,800 bph) and an ETA 2879 (21,600 bph) apart at the same time. I though the non-interchangeable parts would be easy to tell apart. The wheels were, the 2879 escape had more teeth on the pinion, the 2878, the fewer; the 2879 fourth wheel had six spokes, the 2878, eight, the mainspring I figured would be too similar to tell apart so I kept them segregated. I was picking and choosing the best (cosmetic) parts to be build up.

The pallets looked the same. When I put the two back together, one ran about a minute fast, the other a minute slow. That was when I went line by line through the bestfit parts numbers to see exactly which parts where actually the same.

Turns out only five parts are different and the sped changes: mainspring, pallet, fourth wheel, escape whel and the balance assembly (complete, or if you can vibrate a hairspring to match it to the existing balance/staff assy, spring and roller table.)
So... if on two different movements, the frequency is the same, the balance assembly is the same, and the escape wheel is the same, then the pallets must also match, but... if differences are present they could very likely be too small to recognize. Tricky.
 
1 - 7 of 7 Posts
Top