7750: Chronograph Service

Working on the ETA 7750 already puts us ahead of schedule compared to many traditional watchmaking programs, but lubricating and adjusting the chronograph puts us firmly into the realm of advanced watch service.

 The chronograph mechanism is an incredibly complex system of cams, levers and springs, all of which need to interact precisely and without friction. This requires delicate adjustment and careful lubrication.

If you look at the picture above, you shouldn't notice any grease—but believe me when I tell you that it's there! Any surface that contacts another one has oil on it, but the goal for a watchmaker is to make it invisible.

Many 7750s live their lives behind see-through ("display") casebacks, wherein the customer can see the inner workings of the movement. If grease was visible, it would be immediately noticed and rejected by the wearer. Watchmakers strive for cleanliness at all times, since sloppy oiling can cause undue wear and damage, but display casebacks make perfection a requirement.

This was my first time properly oiling the 7750. Previously, my instructor had me try to figure it out on my own. That's not a punishment—it's an integral part of the learning process. This time went a lot better. Practice makes perfect, and the proper oil (Molykote DX instead of MR4, for those keeping track) does as well.

The greatest friction in a watch occurs when two like substances contact each other. Most pivots are steel, rotating in a synthetic ruby jewel. These are oiled, but the difference in materials allow a certain amount of slip. In a chronograph however, many components are steel-to-steel, which can bind and seize in moments. Proper lubrication is key, and if done wrong, it's noticeable almost immediately.

I'm glad to have all the extra practice that our program affords. The 7750 is both incredibly demanding and extremely common in the field. We'll be tested on these sooner than you might think!