The Micro-Mechanics module of the course was now complete and we moved on to the next part, preparing for the gear train exam. We will also get opportunity to work on our school watches along the way, when it links in with what we are learning. It was exciting to know that we would finally get to work on some watches, the first six months of the course is focused on learning how to manufacture parts.
The gear train exam was only a few months away so we would learning about how the gear train works and how to service it. Before this, the building of our school watch requires us to rivet our own train wheels, with the exception of the escape wheel. The wheels that need to be riveted are the centre wheel, third wheel and fourth wheel. The escape wheel is too small and delicate for us to rivet so we use a factory assembled wheel in our watch.
To rivet the wheels we use a staking tool, the arbor containing the pinions and pivots is placed in the base of the tool and the wheel placed on the arbor. A flat stake larger than the unformed rivet is used to first seat the wheel and ensure its flat. A smaller domed stake is used to form the rivet, courtesy of a few taps from a hammer. Finally a flat headed stake is used to flatten the rivet, the wheel is then checked to make sure its running true on the arbor using a true poise tool.
The riveting process is pretty straight forward, the key is to select the correct stake and also apply the right amount of pressure with a hammer. Hitting the stake too hard can damage the wheel by forcing the arbor out through the other side. Likewise selecting the wrong stake can damage the wheel or arbor. I have to admit that I damaged a few wheels before I had three that could be used in my school watch.
This video, courtesy of Roger Smith, from 4.05 onwards shows the process of riveting the wheels although for the burnishing process we use a traditional jacot tool as detailed in my previous posts…
The pivots of the wheels must be burnished in order to reduce friction when the wheels are fitted between the jewels in the main plate and bridges. The pivots on wheels produced at the ETA factory in Switzerland are burnished using a chemical process, we aren’t afforded this luxury so a jacot tool is used to burnish them.
The burnishing process is more difficult compared to pivot gauges and winding stems as there are no carriers available to secure the wheel. It must be held by the spike on the jacot tool in order to rotate it, this makes it prone to falling off if the burnisher is tilted even the slightest bit sideways. Its also easy to mark the wheel with the side of the burnisher as the pivot is so close to it. I marked a few wheels during the process but eventually I have three that are useable.
Although replacement wheels in modern calibre’s mostly come riveted from the factory, I may work on vintage calibre’s in the future where parts are unavailable and wheels need to be re-riveted due to broken pivots or pinions. In my opinion, learning processes like this are what separate skilled watchmakers from technicians and its important to keep traditional skills like this alive. I thoroughly enjoyed the process and I was left feeling even keener to get to grips with some watches!