Is your mechanical clock not running as well as it should? Does it stop intermittently or not run at all? Chances are there is pivot wear.
Occasionally you will see punch marks made to close the pivot hole. Though not an accepted general practice today this was a typical method of repair employed by past clock repairers
Pivots are the ends of the axles (the horological term is “arbours”) that spin in small holes drilled in the clock plates as the clock runs. They are reduced or turned down end of an arbour. These, along with the holes themselves, can become worn. The pivot hole must be perfectly round and the pivots must have a mirror-like polished surface in order to minimize friction within the train of gears.
A worn pivot or worn pivot hole causes the gear to slowly move away from the pinion and it will eventually stop when the gears no longer mesh properly. A clock that is in need of bushings runs erratically or stops altogether.
If a clock movement is not serviced (cleaned and oiled) routinely there will be wear in the plates of the movement where the pivots come through. Worn pivots are typically found in clocks which have been oiled over and over again and not cleaned. The new oil frees up the abrasive dirt and keeps grinding away at the steel and the brass bushing hole.
Pivots must be cleaned and polished periodically to ensure they can turn freely within the hole in the clock movement plate. A worn pivot hole is easy to observe as they usually are oval-shaped instead of round as you can see in the next photo.
The process of Bushing consists of replacing the worn brass around the pivot so that the hole is round again. A new hole is drilled into the plate. A new, properly sized, bushing is punched into the plate using a bushing machine such as a Bergeon Bushing machine. Some clock-makers prefer to hand bush but a machine simplifies the task.
Worn pivots which are made of steel must be replaced with new pivot wire. This is called re-pivoting in clock circles. Minor wear is tolerable and can be addressed by careful filing and burnishing.
Bushing is an important aspect of servicing a movement. Bushing a clock is one of the most fundamental tasks of the clock-maker. Pivot and bushing work work performed correctly will extend the life of a clock movement while ensuring that your clock runs reliably for years.