As is often the case at West Dean, a previous student had already done some work on this project before it arrived on my bench. The escape wheel had been written off as scrap and the process of manufacturing a new one had already been started.
Close inspection of the escape wheel confirmed the damage; each of the teeth were bent outwards at their fragile tips. This was likely the result of a previous repairer’s mistake of removing the balance with power still in the mainspring, causing the escape wheel to spin freely and knock against the locking jewel. In any case it was not the result of normal wear and tear. The clock ran terribly, with poor locking and low amplitude.
Nevertheless, I felt it a shame to discard a nearly 200-year-old component that was otherwise in good shape. These are no longer made in any significant numbers today and so there will only be fewer surviving historical examples in the future. The chronometer as a navigational instrument became obsolete ever since the sun set on the British Empire, and modern quartz technology surpassed mechanical timekeeping. As a relic of a bygone era, the socio-historical significance of this particular example is further enriched by its presence in a domestic clock, for no apparent purpose aside from ‘bling’. It’s the living culmination of values and features that its contemporary stakeholders considered to be desirable enough to warrant a high price tag, and prestigious enough to brandish the names Arnold & Dent – a joint business venture by two well-known chronometer makers.
Wearing my conservation hat, I decided to attempt to save the wheel before diving straight into producing a new one. It is technically challenging to achieve the latter, and I also suspect that damaged chronometer escape wheels outnumber horologists that possess the required manufacturing facilities. It might therefore prove useful for other horologists to design a possible method to fix the issue.
The key points determining the success of this treatment are:
- The restoration of the original geometry of the teeth
- The preservation of historic material.
With this in mind, the following method was designed:
- File a brass block to fit exactly within the gaps between the teeth, matching the front, back, and circumferential profiles as shown in fig. 4.
- Polish with lapping paper to avoid scratching the teeth.
- File the brass flush with the side profile of the teeth.
- Make a burnisher with a mild steel taper pin, polished longitudinally with 1000 grit emery paper.
- Hold a tooth with the brass support block in a watchmaker’s vice, using masking tape on the jaws to prevent scratching.
- Holding the burnisher in a pin vice, gently roll it along the back taper of the tooth starting in the direction as shown by the arrow in fig. 5.
- Repeat 4 and 5 until all teeth are straightened.