6498 School Watch Bridges- Marking, Cutting and Filing

We received some of the first parts for our School Watch a few months back, this included the ETA 6498 blank that is removed from the start of production at ETA specifically for the schools. We receive a blank that has all the bridges marked out and the jewel holes, etc pre-drilled. The next step in the ETA production line would be to cut these bridges out, we will be doing this by hand which will enable us to create our own bridge designs.

The Blank…
The Blank underside…

As detailed in my previous post, I plan to create a movement with a three quarter plate so the normally separate train bridge and barrel bridge would become one bridge in my movement. The plan would be to separate the balance cock from the blank, cut out the three quarter plate and then shape both to my design. This in principle sounds rather easy but there would be quite a bit of work involved before I could see the end result.

The Plan…

Firstly the shape of the three quarter plate would need to be marked out onto the blank, I could then cut the balance cock out using a piercing saw and concentrate on shaping the three quarter plate.

Marked out, the cutting begins…

With the balance cock now removed, I could begin to shape the three quarter plate so that when its fitted to the main plate, the whole balance wheel would be visible. To achieve this I used a combination of files, needle files, sandpaper and a lot of patience!

Ready for filing..

Filing complete and now looking as I had planned, it was time to test fit the three quarter plate to a 6498 main plate. It was immediately clear that there was a slight problem. The semi circle that I had filed to reveal the balance wheel wasn’t centred and more of the wheel was visible on the left than the right. The problem was caused due to me following part of the original cut out in the blank, it was a slightly annoying mistake but things like this tend to happen in the design/production process. So it was back to the drawing board to come up with a solution.

Test fit to a main plate…

After some initial deliberation showed increasing the size of the semi circle to open up the left side wasn’t possible due to the location of the escape wheel jewel hole, my original design would need to be changed somewhat. Studying some examples of 6498 three quarter plates, it was clear that most of them had encountered the same problem. The solution was to curve the left edge of the semi circle to reveal the balance wheel, so I set to work with the file once again.

Modification of the design…
IMG_0812 IMG_0813

You will notice from the photos above, the curve was now in place to reveal the balance wheel but the balance cock and three quarter plate didn’t match… I liked the shape of the balance cock that was left from simply removing it from the original blank. The shape left quite a large space engraving, after I had removed the factory recess, which was what I wanted so I decided to leave it as it was. To achieve a nice flow to the design, I settled on shaping the other side of the three quarter plate to match the balance cock.

Factory 6498 vs mine, this shows the mismatch between the bridges…

After some more filing the bridges were complete. The end result is slightly removed from what I had originally set out to achieve but I’m really pleased with it. I think the two bridges compliment each other well and once decorated should look amazing!

Final design ready for finishing and decoration…

I just need to perfect my decoration skills now and find a top notch engraver that can produce something nice for the balance cock. Hopefully my vision for the watch is now on the way to becoming a reality.

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