These blued steel hairsprings have been made to replicate examples of originals. They fit into the clamp as per the originals. We have produced this spring to have 13 coils, as against the original 12½. This will give scope to slow the clock down further if required. Our test examples have been clamped at 12¼ turns to get to time. You can simply trim the excess to a level to suit yourself.
The internal diameter of the collet seems to vary slightly from clock to clock, so we will make these to the larger dimension that we have experienced with two grub screws to fit.
The readings we should be getting are 2700 beats per hour which you will see from the video is what we are achieving.
The 2700 bph reading we are achieving is with about a 330-degree rotation of the balance. The hairspring is breathing beautifully and is not contacting itself anywhere as it contracts.
It should be stressed that timekeeping on these Eureka clocks is not one of their greatest qualities. There are a number of ways of regulating these clocks, and having the correctly rated hairspring is only one. It is important that all the other components are functioning correctly as simply fitting a new hairspring will not override these issues.
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