The gear train exam would be carried out on the ETA 6498 movement so we were now given the chance to familiarise ourselves with this movement. Following our tutor step by step on the class Camera/LCD TV combo, we got the chance disassemble and then reassemble the 6498 minus a balance. We were given the ETA technical guide for future reference and shown the correct order of disassembly and reassembly.
The ETA 6498 calibre was developed in the 1950’s by Unitas as a pocket watch movement alongside its sister movement, the 6497. Unitas was purchased by ETA who have produced both movements in various guises over the last 30 years or so. The 6498 displaying seconds at the six o’clock position and the 6497 at the 9 o’clock position. Some parts are interchangeable between the two calibre’s, the gear train, main plate and bridges are the major parts that are specific to each calibre.
The 6498 is reliable and robust manual wind calibre but due to its pocket watch origins comes in at rather large 16½ lignes in size. Most modern calibre’s are not only much smaller in size but also include things like automatic winding and a date complication. Where the 6498 really comes into its own though is its relatively simple design and lack of complications. Both these things along with the large size of each of its components make it an ideal calibre to train a watchmaker with.
The 6498 contains 17 jewels, has a frequency of 18,000 BPH (Beats per hour) and a power reserve of 46 hours. Beats per hour tell us the number of times the balance rotates within a 60 minute time span. The length of one beat is one swing of the balance, between reversal, meaning there are two beats in each cycle. 18,000 BPH can be broken down to 5 beats per second.
This video shows how a basic watch similar to a 6498 works…
I thoroughly enjoyed my first taste of working on a watch since I have been at the school, it has helped with my understanding of all the theory we have been taught over the last few months. You can read pieces of paper and look at pictures but theres nothing like seeing the real thing working in front of you. The 6498 being such a simple and large calibre definitely helps you to see how the power in the mainspring is converted into an instrument that can show the passage of time. I can’t wait to learn how to service and repair it in the coming months ready for the gear train exam.