Gents' slave dials

Gents' slave dials could be found in many establishments from schools, to office blocks, palaces, factories, stations, airports and hospitals. The Gents' master clock and slave dial system could be installed anywhere to provide uniform time across a whole complex of separate rooms or buildings. All would be wired in series with the master clock. Here is just a very small selection of the many styles of slave dials available. Some slave movements were even housed in mantle clocks.

An 8" dial with 12 and 24 hour markings and convex glass. The advantage of convex glass is that it diminishes the size of reflected images from windows, lights and skylights. Flat glass reflects the full size of the bright object. Often concealing the clock hands completely. The slave movement from the dial above is show below.

Standard Gents' slave dial movement.  Note the cork insulation pads to reduce noise transmission to the case. Notice also the keyhole cut-out in the hidden hanging bracket. This is common to most Gents' slave dials of normal size. This allowed the dial to be simply lifted free from the wall without tools by lifting slightly. The dial may then be examined, oiled or adjusted and returned effortlessly to its place on the wall. Painters and decorators, made aware of this simple facility, could have saved themselves the difficulty of painting carefully around the dial. Yet many/most slave dials still have repeated paint marks around the perimeters of their cases.

Re-hanging such a dial is a matter of tipping the bottom outwards to peer between the wall and the back of the dial.  You should ensure the larger area of the keyhole is placed centrally over the wall fixing screw. Then lower the dial flat against the wall and allow to sink down the wall surface by half an inch. (12mm)  Now try to slide the dial gently, from side to side. This should instantly confirm that the dial hanging bracket is safely held by the hanging screw in the wall. Pulling gently downward on the dial will further confirm that the screw is safely held by the smaller diameter at the top of the keyhole cut-out. Only then may one safely let go of the dial.

Similar slave dials must have been made in their hundreds of thousands. Providing accurate, uniform timekeeping to government, industry, commerce, education and the health services around the world. The size of the dial would be determined by the distance from which it would normally be read. Or larger still, if it was really intended to be noticed. Like an advertising clock outside a jewellers shop. Or other business, which would hopefully be seen from the other end of the high street.. Sometimes the dial would be oversized if it was important that it should be noticed. Such as at a train or bus station, for example.

The service of providing the time, free of charge, was once much used in advertising and business promotion. Particularly before it became commonplace for the general public to own accurate watches. A time service required accuracy and reliability or the poor timekeeping would reflect badly on the business. The cost of installing a master clock and advertising dial on the façade must have been less expensive, and much less trouble, than a weight-driven turret clock movement. I knew of several shops in one town, in the UK, which all had their own master clock and prominent advertising dials. Perhaps they had a very persuasive, local salesman? Or they each copied each other?   

Many different styles of advertising dials were made to hang outside business premises. Sometimes double sided or even three or four sided. Plain or highly ornamented to taste. Usually with slightly larger, double locking slave dial movements. Or designed to be driven by mechanical lead-off rods from a WT. Depending entirely on the size of the dials involved and whether exposed clock hands were desired.

For corrosive or potentially explosive atmospheres Gents' could provide sealed, very heavy, cast iron dials. These avoided all danger danger of naked electric sparks and resistance to attack or damage. These iron dials are quite popular, when suitable restored, as external dials on the homes of clock collecting enthusiasts.

Here is a 25" diameter example of a cast iron slave dial on an eBay auction. This one is slightly larger than the more normal, 18" dial of this type. This dial fetched just over £250 (Dec 2010) in case you were wondering. It is so heavy than only an adult may just be able to lift it. Normally they would be glazed. On a sheltered wall, or under an overhang, protected from the worst of the weather, they would look much better without the glass. Much more like a traditional turret clock dial.

I once had a smaller example of one of these iron dials but traded it in towards another master clock. The dial was really, quite remarkably heavy. Had it been a slave movement, rather than having a mains motor fitted, I would probably have kept it. Ah, the wisdom of hindsight.

I had a large double-sided station dial, as well, but it was far too large to be of much use to me. Again it was traded towards another master clock. The two slave movements inside looked about the same size as standard wall dials but had double locking. Which made hand setting extremely tedious.

Slave dial hand setting: 

Normally one can just press the armature against the electromagnet core and whiz the hands round the dial by pushing on the large ratchet wheel. One quickly reaches almost to the time to which it is desired to set the hands. Then one releases the armature to relock the movement.  Pressing repeatedly on the armature, against its return spring, will now bring the hands to exact time in half minute jumps.

Usually the master clock is still running and one should allow it to impulse before finally setting the hands to the exact time. Otherwise the dial will show a half minute fast and you will need to go right around the dial again. Hopefully remembering to stop slightly short of the real time. Though I usually insert a fingernail between the armature and electromagnet. Just to stop the movement impulsing for the next half minute. 

Double locked slave dials may have a special lever to aid rapid advancing. Though usually one must resort to manual dexterity by holding the impulsing and locking detents clear of the ratchet wheel. The wheel can then be spun to show the correct time with one's third (or fourth) thumb.

An 18" slave dial with pressed steel case and flat glass. Large enough for an assembly hall, canteen, station, corridor or school gymnasium. The poor weather protection makes it obviously intended for indoor use. Plain baton hands are used here suggesting a later dial. Note the superb clarity of a dial meant to be read from a distance. The distortion in shape is due to the low camera viewpoint. Being indoors the glass reflects no distracting light.

I have taken advantage of another eBay auction to share some excellent images of a Gents "W1" turret clock, slave movement. Don't ask me about copyright. I have no idea where eBay auctions are concerned. It is not my intention to profit from sharing these images or information. One must hope that the seller sees such image borrowing as beneficial during the period of the auction. And won't care after the event.

The usual, back view showing the drive electromagnet, double locking and over-dimensioned components. All designed to handle the heavier loads of larger clock hands over a long period of service. Notice how compact the slave is and how easy it would be to fit into a small recess in a wall. Or behind any partition. See my "bell programmer" chapter for the use of a similar, oversize slave movement to provide motive power for a programmable, time switch.

Side view showing the hour pipe and minute arbor and motion work between the plates. Interestingly, Gents has gone the extra mile and provided a bronze minute shaft and brass hour pipe. Thus hoping  to avoid potential corrosion problems. The movement was supposed to be used with the hands behind glass. However, breakage in an inaccessible situation might mean he clock being required to perform for a extended period in a less than weather-proof situation. Even though this was not the manufacturer's original intention it was guarded against from long experience.

The length of the hour pipe and minute shaft suggest it was designed to protrude through a wooden building rather than through a brick wall. The seller suggests a 3' dial capacity behind glass. Under the protection of a deep roof overhang or indoors it could manage with exposed hands provided (as always) that they are well counterbalanced. (to void the movement having to lift the heavy minute hands before the hour) Exposed hands subjected to the weather should probably be limited to less than half that dial diameter. Note the complete lack of any ferrous materials which might rust and shorten the life of the movement.

The side which would rest against the back of the dial or perhaps a partition wall. The seller suggests 24V DC minimum to achieve a brisk hand movement from the short, half minute impulse of the series clock circuit.  As always, the freedom from regular rewinding made such movements attractive for inaccessible positions such as gable ends, chimneys, stables or barns. The limitation being that a glass dial cover was highly desirable to protect the hands from bad weather. The limited torque available might not cope well with ice, snow or gales. Here the WT would offer power aplenty but at much greater expense, bulk and complexity.

One serious problem with glazed dials with plane (flat) glass is the difficulty of reading the time through the highly reflective glass. Particularly out of doors where a cloudy sky can completely obscure the time by reflecting in the glass. I do not think glazed dials are particularly suitable for church towers or other raised situations. Where the sky is very likely to spoil the view of the clock hands during many, unfavourable sky conditions. I pass a rural house regularly which has a glazed dial raised high on the façade. It is extremely difficult (and usually impossible) to read the time under any lighting conditions. An overhang above a glazed dial will often help to reveal the hands more clearly by reflecting a dark surface instead of the bright sky.

A sheet copper cased 10" slave dial from 1937. One of a matching, signed pair with the same dates and consecutive numbering. The copper should really be polished and lacquered but I have never quite got around to it. The hands are typically Gents'.

A standard Gents' slave movement from 1937 with green, silk covered, copper wire. 
The two large, brass screws at the bottom are for the low voltage, series, time impulse connection from the master clock. Soft, felt pads help to reduce the mechanical noise from the dial makes when stepped forwards by the electromagnet at each half minute.   

An 8" dial with a convex Bakelite case and convex glass typical of office and classroom. I can still remember the long delay between the half minute clicks of the slave clock during the more boring lessons at school. Since I was usually so well behaved it was a once-only treat to watch the master clock and programmer in the headmaster's office while waiting for his return.

Dials were also made with seconds hands but these needed extra components in the master clock. No doubt the noise from these dials dial could be a problem in some circumstances. Gents provided silent movements as part of its range where any noise was a problem. Such as in radio, TV and music studios. 

Gents' also made mains, synchronous motor, driven dials. Often of exactly the same outward appearance as the impulse slave dials. These mains dials were only as reliable as the mains frequency itself. So these dials could not guarantee the uniform and accurate timekeeping of the master clock controlled, impulse system. A power cut (outage) for any reason, would stop the mains driven dials. These were usually made non self-starting to avoid a working dial showing completely the wrong time. Over a large building the effort and expense involved in caring for mains dials could be prodigious. Just as it would be today with (supposedly) cheaper, independent, quartz dials.

An impulse clock system would usually have trickle charged, backup batteries and happily continue running for the duration of the power cut. Synchronous mains dials can usually be recognised by a motor starting and hand setting rod or knob protruding from the bottom of the dial case. Though not always. So if you do find a dial for sale ensure it matches your needs by checking around the back. It should be obvious whether a standard, rectangular, Gents' Bakelite cover conceals a slave movement. Or a tin can is hiding a synchronous electric motor.

Those seeking more examples form the entire Gent's, impulse clock system, by an acknowledged expert on their history and components, should visit the following, beautifully illustrated, website:


Different Gents' dial movements:

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Unknown said...

Hi Chris. I am currently researching the restoration of a complete Gents Pulsynetic Master Clock with one small slave and four tower clock slaves. They owners want it returning to it's 1928/30 spec and look. It was converted to a modern clock controller for the tower slaves 8 years ago with the Master Clock disconnected. I have photos etc. Any literature or guidance will be gratefully received! Wayne Francis, Clockwise Restorations UK.
awf24k at hotmail for com

Chris.B said...

Hi Wayne,

I see you have very wisely joined an expert forum.
Where you will get far better advice that I can manage alone.