Reply To: Unknown gear – Seth Thomas movement

[Bob Tascione]

Hi Jimmy,
William is correct. That is a “stop works” arrangement. It serves two purposes. One is to prevent forcing the spring too far when winding. The other and most important is to help the spring deliver an even, steady amount of power to the movement. When you look at a torque curve of a normal spiral mainspring you’ll see that the drop in force when unwinding is non-linear and is much more consistent after it’s been unwound a turn or two from full wind. The final wind delivers far more torque than the previous turns as the drop in power is non-linear. Also the “drop” in force is very rapid when nearing it’s last winds. This stop work will allow the spring to work between these two extreme points. When setting this stop work up I wind the spring fully with the locking finger lifted away from the locking wheel and then back the spring off one full turn. I then set the stop works up so the finger is in contact with the locking surface (the wider section of the locking wheel which is at about 4 o’clock in your picture). The finger can now enter into each slot, indexing the locking wheel forward by one slot with each rotation of the winding arbor for 6 or 7 slots until it’s stopped once again by the locking surface.

Hope this helps Jimmy,
Bob