Repairing a broken tooth on the escape wheel of a 300 year old clock by Patrick Gordon of Edinburgh.
The “tick-tock” originates where the escape wheel teeth act upon the escape lever pallets.
In this view, the slanted fracture line has been filed flat to facilitate sawing.
The leading face of the tooth is cut down through its length, into the root, leaving the rest of the tooth to butress the new brass.
The notch cut below the root, in combination with the additional support that will be provided by the remaining portion of the original tooth improves the stability of the new metal.
A new piece of hard brass is precision-cut, and lightly tapped home. The new brass is taller than the nearby teeth, precluding contact between the hammer and neighboring tooth tips. This will be followed by low-temperature soldering.
A set of reference measurements is taken from the leading edges of the existing tooth pairings. Excess solder that has been drawn through during heating will be removed in subsequent operations.
The excess metal is marked for removal. This initial mark errs on the side of being minimal, to reduce the chance of removing too much material during the rough cut. Subsequent removal will be more precise and finely finished.
Excess material is removed with a precision flat file, from the flat, front face of the new tooth (first cut).
Excess material is removed with a precision curved file, from the sloped trailing face of the new tooth (first cut).
Care is taken to avoid removing material from the surface of the original portion of the sloped side of the tooth.
The tooth tip is filed down until it matches the height of the rest of the original teeth. This final height is a critical measurement, and it will be verified before the restored wheel is place in service.
A final reference measurement is confirmed, for the final, precision shaping of the tooth. This view reveals that additional material still requires removal from the flat edge of the tooth. The wheel has now also been cleaned up on the lathe, making the joint where new brass meets old almost invisible.
After verifying that the finished tooth height is correct, the tooth tip thickness shows that the tip dimensions are correct; it matches the thickness of the original tooth tips, as shown by the reflected light. The vise is lined to prevent marring.
The new tooth is finished. In this case it was decided to omit replicating the original detail of the scribed radial line, as a way to differentiate the original maker’s work from the new, and more easily identify where the wheel has been repaired.