Adjusting For Isochronism And Positions

[WillFly]

One of the requirements of US Railroad Approved pocket watches is that they have been adjusted for isochronism and at least 5 positions.

 

Is it possible to describe what the watchmaker has to do in the mechanism to make these adjustments?

 

If it's too complicated to do so in so many words, I quite understand - perhaps there's a book which explains the process...

 

Ah - just spotted this: http://mb.nawcc.org/showwiki.php?title=Watch_Adjustment

Edited January 30, 2014 by WillFly

[Mark]

Positional error can be produced by many factors but the main reasons are to do with

 

- Lubrication - too much can be as bad as too little.

 

- Magnetism.

 

Once those are resolved and the watch still shows positional error:

 

Error between dial up and dial down: The balance staff pivots are most likely at fault. Either bent or require rounding (speeds up) flattening (slows down)

 

Then there is side positions where the weight of the balance comes into play - this is where it is important for the balance assembly to be in poise. I say balance assembly and not just the balance wheel as the hairspring, and roller also can affect poise.

 

There are other factors which can affect timekeeping in different positions but these are the common ones.

[WillFly]

Error between dial up and dial down: The balance staff pivots are most likely at fault. Either bent or require rounding (speeds up) flattening (slows down)

 

Ah - I've had two three watches where the movement runs like a train face down, but runs slow or even stops when face up...

[Mark]

Hmm... That can also be a symptom of the balance staff pivots being too short and thus there is too much end shake (movement up and down between the endstone jewels). This can cause the balance to foul the pallet cock with dial up (effectively stopping the watch) or the balance spring to foul the centre wheel in dial down (which can cause the watch to gain drastically or stop it).