**** Ulrich Bretscher's Pocket Watch Page ****

Home

ubub



Key wound watch with lever escapement
From scrap to new glory

Dimensions of the watch:

Watch diameter: ....50.0 mm
Movement Ø:
........43.0 mm
Thickness:
.............15.0 mm
Weight:
..................79 g

An elegant dress watch, ca. 1840-50. Anonymous manufacturer.

Indications: Hours 1- 12, Minutes, Seconds

Fig. 1 and 2: Quite a challenge to repair it! Watch before and after renoval.

Watch lying on a 10 millimeter grid. Left in the state I bought it for SFr. 20.- (US$ 17), right after its restoration plus 22 hrs. of labour.

Apparently the former propriator once has replaced the lossed pendant ring by a twisted wire. And after the mineral glass and the main spring were finaly broken the no longer used watch probably sleped 100 years unprotected in a dawer, where the minute hand was badly bent and the pivot of the second hand was broken.

Movement #30217

Plates from brass with 15 rubies. Beautyfully blued screws. Wheels from brass, save the club-tooth escape wheel which is from steel. There is no back plate. For faciliating the maintenance and repair of the watch all wheels are mounted in single cocks or bridges (=bar movement). The going barrel has only one bearing, with the rim of the barrel sunk into the top plate which gives the barrel additional support. The winding of the main spring is limited to four revolvings by a maltese cross.
The single roller roller balance is temperature compensated (bimetallic) and has an oversprung, flat, blued hairspring. The lever is of the crosier tangential line type, typical for this periode. The crosier "handle" is necessary for balancing the excentric lever. (Modern Swiss watches, as a rule, have staight line levers.)

Fig. 3: Bar movement with a bishops crosier tangential lever. Fig. 4: Top plate (dial side). Here the cover of the going barrel is visible with the maltese cross for winding control on top of it.

The purpose of the maltese cross

Maltese crosses were used in high quality watches for enhanceing the accuracy of time keeping. In about four out of five watches you are buying on the antiques market, the maltese crosses are missing.

Fig. 5: Detail of the maltese cross gearing

The fingered disc is connected to the arbor shaft of the main spring. With each revolving of the arbor, a maltese cross bar is switched forward one by one. The last, fifth bar, with the hump-back will finally stop the rotation of the barrel, as shown in the photo on the left. This way the barrel is limited to four revolvings.

Usually a going barrel of any common watch makes five revolvings for full winding. As shown in the following diagram, within the first half revolving the torsion moment decreases rapidly. Then, between 4.5 and 0.5 revolvings the motion force of the spring is more or less even. Finally the motion force falls rapidly to zero.
And note: Also the time keeping of a very sophisticated escapement is dependent on the motion force of the spring.
So, by limiting the revolvings of the barrel in-between 0.5 and 4.5 revolvings we have a more or less constant driving force of the watch movement and hence a more accurate time keeping.

Fig. 6: Diagramm of the motion force dependant of the number of barrel revolvings.



Only the force between the dotted lines of this diagram will be utilized by this kind of watches, taking into account that the running time of the watch will be reduced by 1/5th by this.




Watch Case #30217
The serial number of the watch case and the movemet are identical. A hint they both were made ba the same manufaturer.
The case is made from 800 fine silver, the same alloy as the Swiss silver coins were. The case consists of a hinged bezel, the dust cover (cuvette) with two key holes in it, and the back. The hinged back is guilloched with a plate in its center for engraving initials. For winding, the back of the watch has to be opened by fingernail.
There are some watchmaker marks inside the back, all written by a Swiss hand. Proof, the watch has seen repairs before.

Dial
Enameled copper base plate with inset second hand dial. Two copper feet for fixing it to the movement. Black roman numerals. The spade hands are original, save the minute hand I repaired.

Bought: On a flea market in Switzerland for Fr. 20.- (~ US$ 17)


Repairs (Warning: This narrations will go into details, may be boring to non tinkerers)

Quite a lot of repairs and replacents were necessary for restoring this scrap watch operational again. As there are:

Replacement of the main spring. The main spring has been broken what ensued a broken tooth of the going barrel. With force 20 the main spring once has been a repalcement itself. It was too strong by far, what caused unecessary wear of the wheels and a recoiling escapement wheel. Now I replaced it by a force 17 spring. (The force of a watch spring is given in 1/100th of a millimeter. Force 17 then is 0.17 millimeter)

Repairing a broken tooth of the going barrel: Caused by the shock of the braking spring the toth which was engaged with the first wheel then was badly bent and showed a crack at its base. So it had to be replaced.


Fig. 7: Repaired going barrel laying on a 10 mm grid.

There are three qualities of brass tin available: hard, middle- hard and regular. For a durable replacement I chose the hard quality (but brittle).
In this case a tooth is
0.30 mm thick
1.15 mm broad, and
1.8 mm high
At first I filed off the stump of the remaining tooth and sawed a slit into the barrel there with a 0.28 mm watchmaker saw blade. Then I filed a flat bar from hard quality brass, about four times as long as required by the size of the tooth; the formost part of it bevelled a bit, so I could wage it into the saw-slit. Then I soldered the tooth with gold useing my jeweler hydrogen-oxygen torch. Soldering with gold is easier than with brass or silver because it flows best. Then I shaped the fresh tooth according to the original teeth. The new tooth now looks like all the other teeth, so I don't think a collegue repairing this watch after another 150 years will notice this replacement at all.

Repairing the going barrel arbor: On key wound watches the squares of the arbors very often are badly worn. This comes, because the users weren't useing a tight fitting key. When not inserted properly, such a key sometimes allows the square slipping inside the key cavity. That causes worn edges of the sqare and finally the square is rounded so much that winding becomes increasingly impossible.
In this case a watch maker files the worn arbor-square until a new square is formed again. But after this repair the square will be smaller than the square for setting hands! The latter one is worn hardly, 'cause its friction is far less than the one of the going barrel. From now on the bearer of the watch will be forced to use two differet keys, one for winding the watch and one for setting the hands.

Replacing the ruby pin of the balance-roller: The escapent of the scrap watch still was in surprizingly good shape. Only the ruby pin was missing. So I fixed a new ruby. This is done by glueing it with shellac in its original position. Shellac is the shit of a paticular kind of lice, having a melting point of 90 to 100°C.

Replacing the mineral glas:

A new ballance endstone:

Photos of how this is done will be added later.




Bought: On a flea market in Switzerland for Fr. 20.- ($ 17)

New Dec. 2007