Wednesday, 5 September 2012

Watch revival No. 6

1916 17J Silver Trench Watch

This is a trench watch from the first world war (most likely owned by a soldier - the luminous painting on the numerals and hands implies military use). The hallmark dates it to 1916, it's 35mm diameter and has an unsigned 17 jewel, adjusted Swiss movement.

It caught my eye for a couple of reasons - firstly because it's a three piece screw case, so an early attempt at sealing the case from the elements (and especially water). The case is made by Dennison who were a Birmingham company who produced high quality watch cases from the late 19th century up until the 1960s. Sadly (and tellingly) there are a number of rather deep gauges which are clearly marks from someone trying to open the case with a knife (i.e. they assumed it was a press-fit case, like the vast majority of early watches were).

The second thing that I liked about the watch is that it has 17 jewels, rather than the normal 15. This means that special case has been taken to ensure good running. The movement is also marked "adjusted" meaning that the balance is made in such a way as to negate the effects of temperature. This was done by making the balance from a sandwich  of two metals with complementary heat coefficients, so as one expands [link for explanation of temperature adjustment].

Having 17 jewels on a watch of this period is pretty rare and would have commanded a significant premium on a regular movement. The 'extra' two jewels are on the centre wheel pinion, you can see the upper one in the very centre of the movement (jewel number 17 is on the dial side of the movement). As I understand it the reason this is rarely jewelled are twofold: firstly there's not a lot of metal to work with as the bridge is very thin at this point (and the jewel needs to be large for the centre-wheel pivot), The second reason it wasn't often done is that it's not really necessary - the centre wheel pivot turns the most slowly of all the wheels in the gear-train (one revolution every twelve hours).

Anyway I cleaned the movement and reassembled, it was fairly straightforward except I neglected to put the dial feet screws in place before I started reassembly. As these have to sit beneath the bridges I had no choice but to backtrack in order to get them in the right place.

After assembling the movement kept ok time (but it was gaining a few minutes per day), so I took it to Richard Edwards for expert diagnosis. He manipulated the hairspring a bit and managed to get it to around +- 20 seconds per day, which is excellent performance from a watch of this age.

One final observation about this watch is that it doesn't appear to have been serviced very often as there are none of the tell tale repairers marks scratched into the caseback. It must have been serviced at some point because the crown is a replacement.

No comments:

Post a Comment