Friday, 22 January 2016

Restoring a Silver Watch Case

Click on the images to see a larger
A while ago I posted a description of how a watch movement is cleaned, in this post I explain how I restore a silver watch case. The case in question was made by John Woodman of Smith St, Northampton Square, London in 1888.

From the wear pattern you may be able to see that the back of the case is depressed, there is also a dink bottom left and there is a lot of pocket wear, in reality it actually looks worse than in the picture. So something had to be done.

The first stage is to get rid of the worst of the muck and oxidisation, this is done with silver polish and a glass fibre brush.

If this were not done the next stage would not work as effectively and the fluid would have to be changed more frequently, perhaps after each case.

The ultrasonic cleaning is primarily to get into the parts other processes cannot reach including into digs and scratches. The fluid bath is detergent based and the case will stay in for 30 minutes which seems about optimal for a silver case.

The second ultrasonic machine shown is loaded with a solvent based cleaner that I use for cleaning movements.

The next stage is to press, rub or hammer out the back and the dents. This process will be different depending on the way the case is made and any finish such as engine turning on the back. Swiss cases in particular are sometimes made with a bezel similar to that on the front with a silver disk inserted - if you press on that to hard it will come out and be a devil to get back in and it you hammered the edge probably impossible.

It is better to press or rub rather than hammer as it will cause less damage to the inside which is difficult to burnish out due to the shape of the case and the necessity of preserving the hallmarks. The amount of work done on the outside has therefore to be balanced with the amount of damage to the inside and possible distortion of the case which may or may not be readily correctable.

The picture above shows the case after this work, the dink still visible but it is now more of a scratch or dirty mark.

For a case with a smooth back now comes burnishing with increasingly finer abrasives. A balance has to be struck between the amount of silver removed compared to the gain achieved in appearance and possible loss of structural strength.

In general I do not try and take out all of the marks but to still give a nice finish. All of this is done by hand.

Wednesday, 20 January 2016

Ten Louis Brandt and Frère - Omega & Labrador watches.

In the last couple of months I have been able to buy in more "Omega's" than I normally would expect to get in a year, here are most of them, 2 at Brackley missed the group shot. They vary in size from approximately English size 10 to a rare size 18. 

They date from 1897 through to 1922 and all are essentially the classic François Chevillat 1894 designed Omega movement and have 15 jewels with a Breguet sprung cut compensating balance with double roller.

Two from 1900 are unusual in that they carry the Omega name or Logo but have screw mounted jewels on the top plate and a screw micro regulator and are therefore the higher grade Labrador in all but name, but this is before LB&F changed the company name to Omega.


Saturday, 2 January 2016

The Safety Pinion (Fogg's patent)

A Reversing Pinion prior to assembly.
The Safety Pinion originated in 1865 when it was usually described as "Fogg's patent", it was intended to avoid damage to the movement in the event of a mainspring breakage, the spring being let down too quickly during maintenance or following failure of the click (ratchet stopping the mainspring arbor from "winding down" and forcing the barrel to move instead).

The problem was that with the very strong springs required at the time the backlash after a failure would go through the train and potentially break weaker parts, mainly I suspect the lever pallet and pallet jewels.

The solution is quite ingenious. Instead of the centre wheel pinion being fixed to the wheel / staff it is screwed on. In normal use the gear teeth on the mainspring barrel bear against the pinion and keep it screwed down.
A "Reversing Pinion" during assembly
but not yet screwed on.

If the pressure is suddenly reversed the pinion unscrews and no reverse power is applied to the rest of the movement.
This solution was initial used by Waltham and then by Elgin who presumably licenced it, but by the 1890's, if not earlier, the concept was more widely used in the USA (the example shown is from a Seth Thomas of 1896) and by a number of the larger makers in England including The Lancashire Watch Company and William Ehrhardt.

Waltham later introduced the "Safety Barrel" to address the same problem but as the amount of power a watch required reduce with the introduction of lighter movements, improved manufacturing tolerances and more jewelling, there was no longer a real need and safety pinions were discontinued.