Buchanans of Chelmsford – Double Pendulum Regulator No. 4

I recently had the privilege to carry out some work on ‘No.4’ by Buchanan.  This tour de force of horology was originally conceived as a homage to the very best of 18th century precision horology taking inspiration from some of the finest work by makers such as Janvier, Breguet, and Harrison.  The design is based heavily on Breguets masterpiece double pendulum clock in the Royal collection No. 3671, with the dials and weight being based on that design. 

I describe this regulator as the greatest hits of horology – turned up to 11!  It is in my personal opinion one of the finest examples of clock making in the modern era.

The regulator had been in America for some years before being shipped over to the UK where it has been ever since.  It had been giving reliable trouble-free service up until just before the work was carried out when it began to give problems, hence the need for maintenance.  The regulator is now 15 years old so it is understandable that servicing should be necessary, but on dismantling the clock a certain amount of damage was found.  This was mainly cracked jewel holes and bent anti-friction wheels, damage that probably occurred during its trip over from America.  I carried out restorative maintenance and fully serviced the clock as the client wanted it returning to ‘as new’ condition.

Escapement

The escapement is a form of gravity escapement of Buchanans own design.  Because the pendulums are only receiving impulse in one direction a conventional escapement would only be able to display 2 second intervals on the dials, so in order to give a true seconds indication an extra layer of complexity was required.  This is in the form of a secondary count wheel which is powered with its own helical spring remontoir similar to that used in escapements designed by both Airy and Aitkin.  The count wheel is unlocked on both sides of the pendulums swing but is only ‘recharged’ when the train is aloud to run when giving impulse.

Double Pendulum Anti Phase

The two movements are completely independent of each other, with the exception of sharing the driving weight.  Each movement has its own pendulum, however both of these pendulums are suspended from a common suspension point.  This enables a phenomenon often referred to as ‘resonance’ to occur.  The two pendulums share each other’s natural mechanical frequency by resonating through the suspension block.  This causes the two pendulums to share and transfer energy between each other making for a far more stable rate.  For example, if the front pendulum is disturbed however minutely the rear pendulum with do the opposite in compensation.  The pendulums will then go through cycles of passing the power back and forth until they stabilise again.  This ‘resonance’ phenomenon causes the two pendulums to lock in ‘Anti-phase’ with each other.

Anti-friction Wheels

After the finest of Harrison’s work in his marine timekeepers this clock has anti-friction roller wheels through the entirety of both movements.  All of the anti-friction wheels are jewelled with all jewels mounted in chatons. 

The wheels vary in size and thickness through the movement with heavy gauge being used at the barrel end of the trains and very light weight at the escapement.

Functions and complications

Both movements are a marvel of mechanical complexity, however the actual display complications are limited.

 The left hand dial displays Mean Time, hours and minutes with a dedicated seconds dial below.  It also displays Solar Time with a separate hand.  The solar hand rotates with the Mean minute hand and utilises Breguets system of ‘sampling’ the position of the ‘Equation of Time’ cam once per minute.  The presence of this cam also allows for an Annual calendar disc which is displayed through a cut out section of the dial. 

The right hand movement displays Sidereal Time using a ‘Regulator’ format dial as with Breguet 3671. 

Maintaining Power

The maintaining power is of note as it is a complex design of epicyclical gearing with three pinions to even out the load.  There are also three ratchet pawls.  The design of the planetary gearing cage makes for a magnificent component which even in this clock is barely visible when assembled. 

The case

The case is wall mounted and has large expanses of glass.  It is mahogany veneered with brass binding.  As with the very best clocks the case does not distract from the mechanism and is simply a delicately proportioned way of keeping the dust of the movement.

The case comes with a matching fitted box which contains the two extra sets of dials, the winding key, the pendulum suspension block key, the case key, the setting key and a set of spare parts including jewels and screws.

Dials

There are three sets of dials for the clock, enamel dials of the highest quality after the finest French regulators and particularly similar to Breguets work, solid silver dials in a more English grained style, and exhibition glass dials, engraved and paint filled.  The latter make the dial almost impossible to read from a distance, but instead allow the viewer to delve deep into the stunning complexity of the below dial work and to marvel at its construction.

Pendulums

The two pendulums are of massive construction.  They are based on Harrison’s gridiron pendulum design, but the execution is more in the French style and is reminiscent of makers such as Berthoud and Janvier.  The outer steel rods of each assembly reverse taper as well as being elliptical in section, representing major feat of construction in their own right. 

The front pendulum carries an integrated thermometer with circular bi-metallic strip and rack and pinion mechanism.

Knife Edges

The pendulums are suspended by means of hardened steel knife edges resting on solid synthetic sapphire blocks.  These blocks are massive and must have been extremely difficult to make.  In order to protect these blocks when fitting or adjusting the pendulums an ingenious system of raising and lowering the pendulums is fitted.  By means of a key the user is able to wind an arbor which raises a steel plate and in turn lifts the pendulum cages clear of the blocks before clamping the pendulums against the suspension bracket.  Each pendulum suspension is also adjustable in two plains using a system of pinions and quadrants hidden within the suspension bracket itself.