These images offer a unique and vitally important record of a very rare timekeeping system. Gillet & Johnston are best known [renowned around the world] for their superb bell casting and high quality weight-driven turret clocks. The company still exists to offer turret clock repairs and modern timekeeping equipment.
Clock Makers, Clock Restorers and Bell Founders
Gillett & Johnston - Wikipedia, the free encyclopedia
Gent's and Synchronome must have seemed to dominate their dwindling market as weight driven turret clocks orders became harder to obtain. The previous funds for church clocks and bells from rich Victorian benefactors were probably no longer available after WWI's massive social upheaval.
G&J must have seen the writing on the wall when Gents began to produce their compact and incredibly powerful WT electric turret clock movements. These went on to set numerous records for increased dial size in the early 20th Century.
So G&J came up with their own, unique electrical impulse master clock, slaves and WT designs.
G&J produced a quiet, and now very collectable, master clock of entirely their own design. Relatively few must have been made because they only rarely come come up for auction and usually fetch a very good price by ordinary Gents and Synchronome standards.
These images alongside show an early, G&J master clock. The attractive mouldings on the top and bottom of a master clock case are usually an indicator of an earlier model. The movement design is elegant and relatively complex for a British master clock. Going through several design iterations over time. Note that the slave unit behind its pilot dial has been installed at 90 degrees anticlockwise to its normal position. It is amazing that it still functions as the time indicator!
The movement uses a swinging armature to reset the gravity arm so that no noisy contact takes place. Spring blades are used to further damp any noise produced by the mechanism. It even has an air damper cylinder to soften the resetting of the gravity arm.
It uses a 15 tooth ratchet wheel and gathering pawl like most other British master clocks. A single electromagnet is arranged at the bottom of the movement backplate. Padded stop screws are provided to set certain movement limits. The gravity arm has a roller which runs down an impulse ramp on the one second pendulum at half minute intervals. The gravity arm is dropped onto the ramp by a trip vane unlatched by the count wheel. A long wire and D-shaped jewel draw the count wheel around one tooth at a time on every swing to the right. So that the count wheel rotates once in half a minute [30 seconds.]
Unlike Gents, G&J seems to have made a different WT for each installation. Or so it seems. I haven't seen two the same in the [only] several examples of which I have obtained images. Anybody out there with a Gillet & Johnston electric turret/tower clock in their charge is very welcome to add more images to the very meagre collection in the public domain which I have obtained so far.
These three images are all I have so far of this particular G&J, WT, turret clock movement. The original images were very dark as flash was not used for the photography. The WT movement was obviously still running because the slow exposure has not caught the bob movement sharply. Flash would have frozen the bob in its swing and helped to stop the camera shake visible in the images here. That said, any images, at all, of a movement so rare as a G&J WT are well worth having. I have done my humble best to lighten and sharpen these images using PhotoFiltre.
G&J has obviously used their own metal casting facilities to produce another very solid baseplate for its own unique WT design. The bob is massive and [very unusually] the cylinder is arranged horizontally so that it can swing in the oval cutaway provided in the main plate. This makes for a very compact movement. As does the shortness of the pendulum. Note that this is a working clock and not a perfectly restored example from a private collection. Lots of oil and a little rust are very typical of working turret clocks hidden out of public sight for 100 years!
Working down from the top, the first thing we notice is the use of bearing instead of a conventional spring blade to support the pendulum. The same, robust, construction feature was used on the Gents' Pulsynetic WTs.
At top right is a small electromagnet which we can safely assume is related to the Waiting Train mechanism. The armature is in contact with an L-shaped lever on its right.
The horizontal, main drive shaft is driven by a wormwheel and worm. The worm is mounted on the same shaft [arbor] as the gathering wheel. The gathering, or count wheel, is pulled round a tooth at a time by the gathering pawl. A backstop pawl hangs at the left of the gathering wheel to prevent backwards rotation. I believe the wheel is rotated anticlockwise by the bifurcated gathering pawl.
Unfortunately none of the images is quite clear enough to be absolutely sure of the WT mechanism's actual function. If it follows Gents' practice then the gathering pawl will be briefly lifted out of the teeth of the count wheel by a pin on the count wheel where it is latched. The pawl is then allowed to drop [by a small electromagnet] to its normal [active] position to gather teeth once again. The electromagnet will be activated by the half minute, timekeeping pulse from the master clock.
I think it is safe to assume the following: The electromagnet's armature is horizontal and seems to be hinged on the left. A right-angled L-shaped lever is a two position latch hinged at its 'elbow.' As the count wheel rotates, a pin lifts the L-shaped arm and thence the gathering pallet. The armature will now be free to drop out of the deep notch by gravity. The armature tip will then lock the L-shaped arm safely in a raised position just below the [normal] latching notch. The gathering pawl will slide ineffectively back and forth, for a few brief moments, clear of the count wheel teeth.
Then the electromagnet gets its half-minute electrical impulse from the master clock and attracts the armature. Allowing the L-shaped lever to drop [clockwise due to gravity] so that the armature re-latches the L-shaped arm by the deep notch in its normal position and clear of the gathering pawl. The gathering pawl can now continue to gather teeth to drive the hands on the clock dials. The armature will be raised to its normal position against its electromagnet's core.
It is the precise timing of the armature's release of the [raised] L-shaped lever [allowing the gathering pawl to drop into the wheel teeth] which resets the timekeeping to the master clock's own standard at every half minute. The WT must slavishly follow the accurate timekeeping of the precision master clock.
A Waiting Train movement is not a true clock. It is a rather complex slave with its own driving power for the clock hands but has no timekeeping ability of its own. Take away the master clock's electrical impulse and the WT [turret slave] will gain very rapidly indeed. In fact it must always get to the half minute a little too soon to allow itself to be paused by its own WT mechanism. It is the brief pause in the drive to the clock hands which gives the "Waiting Train" mechanism its name and ensures its remarkably accurate timekeeping ability.
On the left end of the main horizontal shaft [arbor] are the first bevel gears of the lead-off work to the distant dials. A second bevel gear turns the minute hand drive vertically. A typical universal-expansion joint takes up the vertical drive to allow for movement in the building's structure.
The main shaft is supported by sturdy cast brackets. As are the wormwheel and its worm. All very obvious from the images so far.
Well below the horizontal drive shaft is a set of electrical contacts. Presumably they are operated by a Hipp Toggle and V-block mechanism. The exact detail is rather hard to see in these images but the typical Hipp toggle and block may be hidden behind the pendulum rod. The actual contacts seem to be on the left of the two horizontal contact rods. A Hipp switch system allows the pendulum to swing freely until its arc falls below a predetermined limit. The Hipp Toggle drops into the V-block and the contacts are closed. The pendulum is then given a strong push and the pendulum regains its lost arc.
The problem now is deciding how the pendulum is pushed. The top image shows what appears to be an electromagnet coil just below the bob. It is quite possible that G&J decided to use this classic and well proven method of maintaining a pendulum's swing. This same arrangement had been used for domestic and precision electric clocks since Hipp first presented his ingenious Toggle and V-block back in 1843.
I believe the two sturdy horizontal crossbars just above the swinging bob are there to catch the pendulum if the pendulum support should fail. Or perhaps to limit its maximum swing?
Here we see the vertical lead-off rod emerging from the WT movement below to meet the crown-wheel cluster of bevel gears. Another expansion-universal joint allows for thermal expansion of the lead-off rod. The bevel gear cluster is strongly supported by am open, timber framework. Three further bevel gears lead off from the larger crown bevel gear to the exposed skeleton dials. All perfectly standard practice in turret clocks of all types and ages.
A close-up of the typically, very high quality bevel gear cluster produced by master turret clock makers. Note the sturdy, cast, hanging bracket. Each lead off rod to the dials has its own expansion-universal joints. The bracket must support not only all the bevel gears but all lead off rods as well. Including the vertical rod rising from the WT movement on a floor somewhere down below.
Here is a Gillet & Johnston bell dated 1922. Would it be a wild guess to assume that the entire G&J clock installation matches the date on the bell? The bell is struck electromagnetically by a large hammer driven by a powerful electromagnet in the box in the foreground.