The Making of a Chronometer detent

The making of a chronometer detent is just one but an importent tasks of a chronometer maker.

Marine Chronometer GUB Glashuette from 1957

There are many good watchmakter out there. The speciece of chronometer maker nowadays is very rare. But some of the old masters fortunately wrote down there knowledge to pass it on to a new generation. Alfred Helwig is one of these old masters as well as Alois Irk. I used there articles and books to make a new detent to replace the old and broken one of an GUB Marine Chronometer from Glashuette from the year 1957.

Alfred Helwig – Schriften
Article: Making of a detent

First, it was all about reading and studying the dimensions, materials and shape of the detent.

Alois Irk – The detent escapement
Design of a detent escapement

During this time I was analysing an English, a German and a Russian Marine Chronometer.

The broken spring detent

Choosing the right material is difficult already. Helwig only says “using the best material: Huntsman-steel” which only described the method of steel making and not its components. So a research in other sources was necessary.
I found that some Swiss and French chronometer maker use 20AP.  Some English and Australien chronometer maker use 01 toolmaker steel. It is similar to the steel 1.2510 which is used in Germany too as well as 20AP. The Russian chronometer maker use  Y10A (1.1545 or C105W1).

Steel C100S (1.1274)

In the end I choosed C100S (1.1274). It is already tempered and has all the right characteristics for a high quality spring (according Helwigs requirements). The disadvantage is, that this material is more difficult to process because it is already hardened and tempered.

The new raw detent with all necessary holes
Filing and grinding the raw material
Testing the locking stone hole with a pin
Testing the locking stone hole with the rubin locking stone

Filing and grinding of the springy part of the detent.

The springy part of the detent has a thickness of 0.04 mm. But the final test wether it is thin enough will be as follow: The movement including the detent escapement will be put together. Except for the helicoil spring. When the balance is slowly turned the detent will unlock the escapement wheel for one tooth. This tooth will give the balance an impulse. The balance will turn. After 360 degree the same will happen again. If now the balance will accelerate (as seen in the video) the detent spring is thin enough.

RGG Signature – Richard Griessbach Glashuette

Testing the position of the locking stone hole.

Grinding and polishing the surface.

Detent with locking stone and gold spring

Components of the chronometer movement
All components of the detent escapement system
Detent mounted to the detent cock

The first run of the new detent. Now the adjustment work can begin … still a lot of work. The book of Giebel & Helwig assisted my work.

Giebel & Helwig – Fine adjustment of watches
Step by step guide to adjust a detent escapement system
Marine Chronometer movement GUB Glashuette
The performing Chronometer

In the end it was a great experience and learning process, investment in the own craftsman skills and coming one step closer to heart and the art of watchmaking.
Steffen Cornehl

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