David Bond Clock Repairs

The restoration process

This gives an insight into some of the stages of the restoration.

Next, the going train and strike train spring barrels are reconditioned with new bearing surfaces and new springs.

The first picture shows a comparison with the old and new spring. The new spring is thinner and longer giving more uniform power through the week. It is also highly resistant to fatigue cracking.

The barrel arbor (centre steel winding shaft) bearing surfaces are restored to remove wear.

The barrel and cap are machined to accept the new bearing surface (bushing) which is made on the lathe to an identical taper.

The spring is fitted to the barrel and the cap pressed into place using a die.

The original brushed finish is restored and protected with a hard wax polish.

The next stage is to ensure all mobiles (the brass wheel, the steel pinion, the steel arbor and the pivots) are in perfect condition.

The arbors are checked for straightness, the brass wheel is checked for concentricity on its arbor or pinion, and the pivots (the small diameter sections at either end of the arbor) are restored to a perfect bearing surface.

It is sometimes the case that a wheel has to be corrected for concentricity.

The wheel is removed from its arbor or pinion and a new brass collet is made to be perfectly concentric to the pinion. The wheel is bored concentrically to its circumference and the new collet and pinion mounted to the wheel.

In the case here the pinion also had to be bored as it has to able to move on its arbor to enable hands setting. A small brass sleeve was then made to give a perfect fit between the arbor and the pinion.

Once the mobiles are restored and corrected where necessary, work then moves onto the plates. The bearing holes can become slightly elongated or enlarged over time which can result in inefficient engagement of the wheel and pinion teeth. This generates friction and can even stop the clock, or at the least, cause unreliable running.

The wear is corrected using a process known as re-bushing. First, the correct distance between adjacent mobiles is established (a process known as depthing), this distance is transferred to the plate and the hole position established.

The worn bearing hole is enlarged to accept a new hard brass or bronze bearing (called a bush). The new bush is pressed into the plate and the centre hole precisely sized (known as broaching) to give a perfect fit for the pivot. The inner surface of the bush is finally burnished to a mirror finish which has the effect of work-hardening the bearing surface. The beauty of this process is that it can be repeated any number of times, thereby giving the clock an effectively unlimited life. Finally, all mobiles are tested in their positions for perfect operation.

The pendulum is made from brass stock and stainless steel for the rating nut thread. It was designed to be functionally identical to the original lead one. There are four components; the bob itself, the square section rod, the stainless steel threaded portion and the rating nut. There is also an internal spring to keep the bob fully seated on the rating nut and to prevent the rating nut slipping.

All components are now cleaned in a multi-stage process, polished where appropriate to restore the original finish and put through a final cleaning stage. The initial cleaning stage includes ultrasonic cleaning which removes all traces of solidified oil, etc. After final cleaning, all components are treated with a hard wax preservative to prevent tarnishing and corrosion.

The chapter ring (which replaces the original dial) is made from an aluminium disc, printed with the numerals and lacquered to retain the character of the original. This is then bonded to a thick aluminium plate and machined to size. Finally, the small holes are drilled for the pillars. During all these processes it is protected with ahesive plastic film.

The base is made of cast iron, both for stability and to reflect an industrial feel. It is machined on the lathe and the various fixing positions are co-ordinate drilled from the measured dimensions of the clock plates.

The levelling feet are turned from brass stock and threaded for the base. They echo the pillars supporting the clock.

Connecting the movement to base are four brass pillars.

A major constraint in the design was that there must be no requirement for the movement to be altered in any way in order to mount it. This was achieved by an internal clamping system in the pillars.

Another constraint was that they must be extremely rigid (as with all clocks, rigidity is crucial). There are some 25 steps in the making of the pillars.

There are some more parts all made in the workshop such as chapter ring pillars, connecting brackets, brass feet for the glass dome, hands, fixings, etc.

First the trains are assembled, then some of the striking work. The strike operation is synchronised with the time train and all pivots and bearing surfaces are lubricated.

The clock is mounted to a test stand to to verify strike operation for each hour and the operation of the safety features.

The escapement is then set up.

The movement is mounted to the base and the chapter ring aligned. The hands are then synchronised with the indexes and the strike operation.

The pendulum is installed and a timing machine is connected. The beat setting (symmetry of the ticks) adjusted and the initial rate is adjusted over a period of a few hours.

The clock is then tested over a period of several weeks and a record is kept of the timekeeping.

If a pivot is too worn or not restorable it has to be replaced.

The existing pivot is removed and the arbor has to drilled precisely on centre to accept a new pivot. The new pivot is made from hardened and tempered steel (known as "blue pivot steel"). The steel is fixed into the arbor and brought to final diameter and burnished as with existing pivots.

Here, the pallet arbor pivot needed replacing, complicated by also having to make a new crutch collet and friction clutch. For information, the pivot diameter here was 0.6mm.

First, a complete dismantling of the clock, and an initial clean.

I would be delighted to answer any questions you may have regarding the process or other matters horological - please call or email.