reamer – Antique and Vintage Mechanical Clocks

In Part I, I explained the importance of bushing to mitigate wear on a mechanical clock movement.

In summary, bushing involves replacing worn brass around a pivot by drilling a new hole and inserting a new bushing, either using a bushing machine or hand tools. Severely worn pivots may need re-pivoting, which involves installing new pivots using a lathe. Minor wear can be managed with filing, polishing, and burnishing. Proper bushing and pivot work are crucial for maintaining clock movements, extending their lifespan, and ensuring reliable operation.

Now that we understand bushing wear, it is time to proceed with the bushing process.

The process of bushing a mechanical clock plate involves several steps to restore the worn pivot holes to their original condition. Here’s a detailed description of the process:

Disassembly: The clock movement is carefully disassembled, and the clock plates are removed to access the worn pivot holes. Resist the temptation to immerse the entire movement in a cleaning solution. Although this might offer a temporary fix, it prevents proper assessment of the pivots and pivot holes for wear.

indicating wjehere bushings will be installed — _{Wood picks identify where bushings will be installed}

Cleaning of all parts: While manual cleaning with a solution is satisfactory, using an ultrasonic cleaner and a solution specifically designed for such a machine, yields better results by ensuring all dirt and grime are thoroughly removed from the brass and steel parts. The cleaning process also includes thoroughly drying all the parts.

Identifying Worn Holes: Each pivot hole is inspected for wear. Worn holes are typically oval-shaped due to the pivot’s repeated movement. I use a marking pen to identify those pivot holes that require a new bushing. I generally work on one train at a time, leaving the main wheels out during this process. I reassemble all the wheels of one train between the two plates, checking for wear by turning and pushing on the wheels. This allows me to observe any lateral movement and see how the gears mesh with each other.

_{A marking pen identifies a worn bushing hole}

Centering and Drilling: A bushing machine with a centering tool is used to precisely center the worn pivot hole.

Centering prior to drilling — _{Centering tool Centering is used to center the pivot hole}

A new, round hole is then drilled into the clock plate. This hole must be accurately positioned to ensure the clock’s gears will mesh correctly.

Drilling a hole with Bergeon bushing machine — _{Using a cutter to enlarge a hole in the plate}

Selecting the Bushing: An appropriately sized bushing is chosen to fit the newly drilled hole. The bushing is usually made of brass and should match the original hole dimensions but is made larger than the hole to ensure a tight fit. For the Bergeon Bushing Machine, Bergeon brass bushings are used.

Pressing or punching the Bushing: The selected bushing is pressed or punched into the newly drilled hole. This can be done using a bushing machine, which ensures the bushing is inserted straight and flush with the plate. If done by hand, reamers and smoothing broaches are used to achieve a similar result. A chamfering bit, which does not come with the Bergeon Machine, is used to gently cut the edge of the bushing hole to ensure that the bushing is punched or pressed in neatly.

Punching the bushing home — _{Positioning the bushing prior to punching the bushing home}

Reaming the Bushing: Once the bushing is in place, it is reamed to the correct internal diameter to fit the pivot. Reaming is achieved by using a five-sided reaming broach sized to fit the hole. Following the reaming process, a smoothing broach is used to smooth the walls of the bushing hole. A toothpick is then used to clean the hole and remove any debris left behind by the broaches. This entire process ensures that the pivot will rotate smoothly without excessive play.

Swiss made smoothing broaches — _{Swiss-made smoothing broaches}

Polishing and Burnishing: The pivot that will run in the new bushing is polished and burnished to reduce friction and wear. A metal lathe is an indispensable tool for this procedure. This step is crucial for the longevity of the repair.

Reassembly: The clock movement is reassembled, with the newly bushed pivot holes ensuring proper alignment and smooth operation of the gears. Clock oil is applied before the testing phase.

Testing: The reassembled clock is tested to ensure that it runs accurately and reliably. Any final adjustments are made to fine-tune the movement.

The process of bushing a mechanical clock plate involves disassembly, identification of worn bushing holes, precise centering and drilling, selection and insertion of appropriately sized bushings, followed by reaming, polishing, and burnishing of the pivot. Finally, the clock movement is reassembled and thoroughly tested to ensure accurate and reliable operation.

By following these steps, the worn pivot holes are restored, improving the clock’s performance and extending its lifespan.

American Sessions time and strike clock showing a gear pivot and the build-up of dirt in the pivot hole

Is your mechanical clock not running as well as it should? Does it stop intermittently or not run at all? There may be a number of issues with the movement and among them pivot wear.

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. The two surfaces must be protected and the barrier between the pivot and the pivot hole is clock oil.

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. If new oil is applied over the old il it will free up abrasive dirt and keep grinding away at the steel and the brass bushing hole. Worn pivots are typically found in clocks that have been oiled over and over again and not properly cleaned. The term “properly cleaned” implies disassembly of the movement, cleaning the parts, addressing wear issues, reassembly, and testing.

Occasionally you will see punch marks made to close the pivot hole. Though not an accepted practice today this was a common method of repair employed by past clock repairers

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 are oval-shaped instead of round as you can see in the next photo.

Close-up of bushing wear — Close-up of oval-shaped bushing wear. The circle shows what the hole should look like

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, the bushing is punched or pushed into the plate using a bushing machine such as a Bergeon Bushing Machine.

Some clock-makers prefer to hand bush using reamers and smoothing broaches and the results are entirely acceptable but a machine simplifies the task.

Badly worn pivots which are made of steel must be replaced with new pivot. This is called re-pivoting in clock circles. A watch or clock lathe is used for re-pivoting which involves drilling into the end of the wheel arbour with a high-speed bit and installing a new pivot made from pivot wire.

Using a micrometer to check pivot diameter

Minor wear is tolerable and expected over the life of a clock and can be addressed by careful filing, polishing, and burnishing.

X marks pivot holes that need to be bushed — X marks pivot holes that must be bushed

Looks like a large pivot hole but actally punched close to the hole — Punch marks near the pivot hole. This was a common practice of past clock repairers

Bushing is an integral part of movement servicing. Some clocks that have been well-cared for may have minimal wear and may not require new bushings while others, through neglect or improper servicing, may require many bushings.

Bushing a clock is one of the most fundamental tasks of the clock-maker. Pivot and bushing work performed correctly will extend the life of a clock movement while ensuring that a clock runs reliably for years.

Tag: reamer

Understanding Clock Pivot Wear and Bushing: Part II of Two-Part Series

What does bushing a clock mean?

Occasionally you will see punch marks made to close the pivot hole. Though not an accepted practice today this was a common method of repair employed by past clock repairers

Rate this:

Share this:

Occasionally you will see punch marks made to close the pivot hole. Though not an accepted practice today this was a common method of repair employed by past clock repairers

Rate this:

Share this: