Unusual Balance Bridge?

[lpoleshuck]

I've come across a balance bridge support arrangement that I've never seen before. And the funny thing is that I've seen it twice in a row!) I've been working on two watches. One appears French. The second, English. The first has no manufacturer markings, the second only D.F. & Co.

The odd thing is that in each case the balance bridge screws not into the main plate, but instead into a small plate that fits in from the reverse side of the main plate. The balance bridge has two pins to align into this plate. Said plate has, besides the pin holes and screw hole to match up with the balance bridge, a balance jewel (with cap jewel).

Here are links to photos of the balance bridge & backing plate (http://lpoleshuck.home.att.net/one.JPG) and the
back of the main plate (http://lpoleshuck.home.att.net/two.JPG) into which the backing plate fits.

I have not seen this arrangement on the American watches I've worked on and wondered if anyone could shed light on why these watches were constructed with this added piece of complexity. It would have been simpler to have the balance bridge screwed directly into the main plate, so there must have been a reason to do it this way.

Any comments?

--Larry

[lpoleshuck]

I've come across a balance bridge support arrangement that I've never seen before. And the funny thing is that I've seen it twice in a row!) I've been working on two watches. One appears French. The second, English. The first has no manufacturer markings, the second only D.F. & Co.

The odd thing is that in each case the balance bridge screws not into the main plate, but instead into a small plate that fits in from the reverse side of the main plate. The balance bridge has two pins to align into this plate. Said plate has, besides the pin holes and screw hole to match up with the balance bridge, a balance jewel (with cap jewel).

Here are links to photos of the balance bridge & backing plate (http://lpoleshuck.home.att.net/one.JPG) and the
back of the main plate (http://lpoleshuck.home.att.net/two.JPG) into which the backing plate fits.

I have not seen this arrangement on the American watches I've worked on and wondered if anyone could shed light on why these watches were constructed with this added piece of complexity. It would have been simpler to have the balance bridge screwed directly into the main plate, so there must have been a reason to do it this way.

Any comments?

--Larry

[Jerry Treiman]

This looks like it has a cylinder escapement. If so, I suspect this arrangement is so that the depth of engagement between the balance and escape wheel can be adjusted.

[lpoleshuck]

It is a cylinder escapement. However, there is very little play in the attachment of the little bridge to the plate. You might be right about allowing adjustments, but only very, very minisucule ones.



[This message has been edited by lpoleshuck (edited 12-27-2001).]