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Meccano striking and chiming clock mechanisms
(Author: David Couch)
Meccano striking and chiming clock mechanisms
By David Couch, Nelson, New Zealand
Version 1.7, 6 February 2017
About this document
This document is a review of published descriptions of striking and chiming mechanisms for Meccano clocks, with some comments on how they operate. In preparing it I have searched the available British publications, such as Meccano Magazine, The Meccanoman’s Newsmag and Constructor Quarterly. As can be seen, I have found only about a dozen descriptions of striking mechanisms, and yet many articles talk about striking clocks as if they were an established feature of the Meccano scene. Unfortunately very few refer explicitly to anything that has gone before.
There is a great deal more literature, such as club newsletters and magazines from several countries, especially France, that I do not have access to, and so it is likely that there are many other published mechanisms that I do not know of.
So this document is a work in progress, and I would ask anyone who is interested in striking and chiming clocks to contact me with additions, corrections and comments. My email address is firstname.lastname@example.org
In this review I am concerned mainly with articles giving detailed descriptions of the construction of mechanisms. There have been many other references, especially in Meccano Magazine, which give only a picture or a brief description.
General comments on striking mechanisms
Definition of striking: audibly indicating the hour by striking a bell, once at one o'clock, twice at two o'clock, three times at three o'clock and so on, usually up to a maximum of twelve strokes.
If you asked even the most mechanically-minded person how you might build a purely mechanical device to produce the correct number of strokes, as defined above, they would probably have to think for a long time before coming up with an answer. It is not a trivial problem, but over the centuries several workable solutions have been devised. There is considerable intellectual challenge in coming up with a relatively simple, reliable mechanism.
The heart of any striking mechanism is what I will call the counting object, an object which moves each time the bell is struck. The striking stops when this object reaches some limit. A power source is required, which may be a falling weight, a spring or an electric motor. Controls are also required, to start and stop the mechanism. These may be switches or contacts for electric power, or a mechanical block of a movement in the case of weight or spring power. A common feature is the warning, an event which occurs a few minutes before each hour, usually triggered by a trip, cam or switch operated by the movement of the minute hand of the clock. On the warning the mechanism is reset or prepared in some way for the striking operation. The striking of the bell is often caused by a cam or trip on a rotating shaft, which I will call the bell shaft.
Many so-called striking clocks produce a passing strike, which means striking the bell just once at each hour, and sometimes at the half hour and even the quarter hours. While it adds considerably to the interest of a clock, this is a trivial problem, requiring just a cam or trip on the minute hand shaft. I will not describe it further, except to note that the following published Meccano clock designs incorporate a passing strike. Some of the counted strike mechanisms described below also produce a passing strike on the half hour.
Tick Tock Time by Pat Briggs, Meccano Magazine, July 1968, p390
Half-Hour Strike Mechanism by Bert Love, Meccano Magazine, October 1974, p102, and supplement to ModelPlan 120, February 2000
Skeleton Clock by Mike Edkins, The Meccanoman’s Newsmag, July 1993, p20
An Impulse Inching Clock by Dave Harvey, Constructor Quarterly 77, Sept 2007, p24
A Nautical Skeleton Clock by Berco Landman, Constructor Quarterly 96, June 2012, p4
Count wheel mechanisms
The count wheel mechanism, also known as the locking plate mechanism, was the first to be invented, in the fourteenth century. It was largely superseded by the rack and snail mechanism from about 1700, but a few clocks using it have been made since that date. The majority of published Meccano striking clocks use some form of this mechanism.
The counting object, known as the count wheel or locking plate, is a wheel with a series of unequally-spaced slots or projections around its rim. The spacing between the first and second is one unit, between the second and third two units, and so on, with twelve units spacing between the twelfth and first, making a total of 78 units. Some kind of lever is arranged to engage these slots or projections. When the striking starts the lever is lifted. The bell shaft causes the bell to be struck one or more times in each revolution, and through gearing rotates the count wheel by 1/78 of a turn for each stroke. When the lever encounters the next slot or projection the striking is stopped.
A description of the operation of the count wheel mechanism in “real” clocks is at http://mb.nawcc.org/showwiki.php?title=Count_Wheel_Basics&highlight=strike+basics
The controls may seem rather complex, and most Meccano implementations are simpler. Two points to note about this description are that the operation of the mechanism includes a warning, and that the striking is stopped by blocking the warning wheel, which rotates relatively fast with little torque.
The main disadvantage of the count wheel mechanism is that it simply produces a sequence of strokes with increasing number, i.e. one at one hour, two at the next hour and so on, but this number is not synchronised with the time indicated by the hands of the clock. If the striking mechanism is stopped for any reason, when it resumes it will produce the wrong number of strokes until it is manually resynchronised. A further disadvantage for the Meccano builder is that the gear ratio (1:78) required to turn the count wheel is a multiple of 13, and no standard Meccano spur gears give this ratio. I will refer to this as the factor of 13 problem.
The count wheel is sometimes fabricated from Meccano parts, while in other designs a wheel cut from cardboard or other material is used.
The “Electric Chiming Clock”
This clock was designed in 1945 by a French builder, J Bouveau, who submitted an article titled Horloge Electrique Meccano à sonnerie to Meccano Ltd in England. It did not see the light of day until 1999, when it was reconstructed and published as ModelPlan 112, Meccano Electric Chiming Clock by Jim Gamble. It is driven by a synchronous motor, and has a count wheel striking mechanism powered by the same motor. The clock is described as a chiming clock, which may be excused as a mistranslation from the French. It uses a count wheel and a “striking wheel” cut from cardboard or fibreboard. A half-hour passing strike is included in the count of strokes, making 90 in each 12 hours, and so avoiding the factor of 13 problem.
Ron Fail’s Mechanism
A booklet titled An Introduction to Meccano Clocks was published by The Meccanoman’s Club in 1967. It includes a schematic diagram and brief description of a count wheel mechanism designed by Ron Fail. Interesting features are:
• Striking is stopped and started by blocking and releasing the count wheel itself. The text warns of possible problems, which are discussed below.
• There are two separate count wheels, for odd and even hours, and two blocking levers which operate alternately, providing very simple control and making a warning event unnecessary.
• Epicyclic gearing is used to solve the factor of 13 problem.
A more detailed description of the mechanism is given in an article titled Strike Out by Ron Fail, Meccano Magazine, May 1969, p246. It is powered by an electric motor.
The No. 2 Clock Kit
The Meccano clock kits came out in 1971. The No. 1 Kit is a timekeeper only, while the No. 2 Kit is a striking clock. (All the literature associated with the clock describes it as a chiming clock. This is discussed below.)
The manual for the kit can be seen at http://www.nzmeccano.com/image-8438
The No. 2 Kit follows Ron Fail’s design closely. It has several serious flaws, and the kit must have caused frustration and disappointment to many of those who built it. One of the flaws is having the blocking levers operate directly on the count wheels, which consist of two Hub Discs with Angle Brackets bolted to the rims. The torque on the wheels is such that the Angle Brackets tend to bend, so special hardened Brackets were supplied, and the blocking levers tend to stick to the Brackets and fail to drop, in spite of Tension Springs pulling them down.
Improvements to the No. 2 Clock Kit
A number of articles have been published detailing the flaws in the No. 2 Clock Kit and suggesting remedies.
Note no. 247 by Geoff Wright, Meccanoman’s Journal, January 1973, p884.
Modifications to the Meccano No. 2 Clock Kit by Noel Ta’Bois, Meccanoman’s Newsmag 60, July 1991, p4.
Improvements to the Meccano Clock Kit No. 2 by Oscar Fontan, translated by William Irwin, Canadian Special Model Plan CMP3 (old series). This document is now available on-line at
Note: Noel Ta'Bois and Oscar Fontan were apparently unaware of each other's work. Anyone wishing to build the No. 2 Clock Kit should read both of their documents.
John Nuttall’s mechanism
A brief article titled Flail Locking Clock Striking Mechanism by John Nuttall, Midlands Meccano Guild Gazette, April 1980, p13 describes a very simple count wheel mechanism which uses a half-hour passing strike to reset the main strike, so that no warning is required. It is shown as a diagram, and it is not clear whether John ever built a working implementation of the design.
John Wilding’s mechanism
This mechanism, described in A striking unit for Meccano clocks by John Wilding FBHI, Constructor Quarterly 51, March 2001, p22, has a locking plate or count wheel made from cardboard. It uses a warning, and has a simple and ingenious arrangement of two microswitches, one operated by the minute hand and the other by the count wheel, to control the strike. The count wheel is driven via epicyclic gearing.
Wilbert Swinkels’ mechanism
ModelPlan 178, Clock Striking Mechanism by Wilbert Swinkels (2008), describes just a striking mechanism. It features a very large count wheel, based on a Large Flanged Ring, and a Strip bent into a serpentine shape whose only purpose is to support an electrical contact. It is driven by an electric motor. It solves the factor of 13 problem by driving the count wheel with a loop of Chain with exactly 182 (13x14) links. A central part is what is described as the “intermittent linear mechanism” whose function is to withdraw a Rod which locks the count wheel, and then replace it quickly, before the next projection on the wheel comes round. Videos of this mechanism in operation can be seen at https://www.youtube.com/watch?v=La6t59ol3Ng and https://www.youtube.com/watch?v=19UotSqn2y0
Berco Landman’s mechanism
This mechanism, described in Synchronous skeleton clock by Berco Landman, Constructor Quarterly 92, September 2011, p31, operates on the same principle as John Wilding’s, but uses a count wheel similar to that in the No. 2 Clock Kit. An interesting feature is the use of a glass dome cover as a bell.
Mike Edkins’ mechanism
This clock was first published in the Meccano Newsmag, issue 117, July 2010. It features a count wheel consisting of 78 Rods attached to loops of Chain containing exactly 78 links, around the rims of three 3” Pulleys with Tyres, forming a cylinder. Twelve of the Rods are shorter than the others, leaving slots with the appropriate spacing. The result is probably the smallest diameter count wheel that is possible with standard Meccano parts. At the warning the strike is preset. A cam on the minute hand shaft lifts a lever that releases a stop from the hoop wheel (similar to the warning wheel) and lifts a lever up out of the slot in the count wheel. The striking train begins to run but is arrested by another lever that is lifted and engages with a Threaded Pin projecting from the boss of a 19t Pinion, which is in mesh with a 95t Gear attached to the hoop wheel. On the hour, the 19t Pinion is released and the striking train runs until the lever engages with the next slot in the count wheel. This does not block the rotation of the count wheel; that is achieved at the same time when a lever drops into the slot in the hoop wheel. Mike solves the factor of 13 problem by having the count wheel driven by a Sprocket engaging the 78 Rods, which are held at the correct spacing by the Chain.
John Stark’s improvements
The article Modifications to Mike Edkins’ Countwheel Striking Clock, by John Stark, The Meccano Newsmag 122, March 2012, p8 describes a number of improvements to Mike Edkins’ design. A full description of the clock, including John’s improvements, was published as ModelPlan 205, titled Weight-Driven Striking Clock by Mike Edkins in 2013.
Rack and snail mechanisms
The rack and snail mechanism, also known as rack striking, has been the standard mechanism for most "real" striking clocks since soon after its invention in 1676. Its great advantage over the count wheel mechanism is that the number of strokes is synchronised with the time indicated by the hands, so that if the striking is stopped for any reason it can be resumed without manual resetting.
In this mechanism the counting object is a toothed strip or segment, known as the rack, which slides vertically or rotates in an arc. On the warning the rack is allowed to drop until it is stopped by a cam which rotates with the hour hand. The cam, known as the snail, is spiral shaped, with a step equal in height to one tooth of the rack for each of the twelve hours. On the hour, the bell shaft rotates, striking the bell and lifting the rack by one tooth for each strike. A pawl prevents the rack from dropping back between movements. When the pawl drops off the end of the rack the mechanism is stopped. A description of the operation of the rack striking mechanism in “real” clocks can be found at http://mb.nawcc.org/showwiki.php?title=Rack_Strike_Elements
The Master Clock
The first published description of a Meccano striking clock is in an article titled A Meccano Master Clock in Meccano Magazine, September 1935, p536. This is a remarkable creation. It is a full-sized pendulum-driven grandfather clock with striking and chiming as well (more on chiming later). Unfortunately, as with many construction articles in early issues of Meccano Magazine, the small low-resolution half-tone photographs and incomplete description make it impossible to build. However, we can see that it has a rack and snail striking mechanism powered by a Meccano electric motor, with extensive use of electrical contacts and other electrical parts. Instructions are given for cutting the snail cam for the striking mechanism from a piece of sheet metal.
Mike Edkins’ mechanism
The only other published description of a rack striking mechanism that I know of is ModelPlan 184, titled Bracket Clock by Mike Edkins (2009). Mike ingeniously replaces the flat spiral cam, which cannot be made from Meccano parts, with a helical or corkscrew-shaped cam, which can. He uses a Toothed Segment as the rack, and a piece of wire in the end of a Rod With Keyway to obtain the necessary small movement of the rack. The clock is powered by three Magic Motors, is entirely mechanical, and uses only standard Meccano parts.
Hour-seeking rotor mechanisms
Around 1983 Stephen Jeavons devised a revolutionary new type of striking mechanism which owes nothing to either of those previously described. I have coined the term hour-seeking rotor mechanism for it. The heart of the mechanism is a shaft carrying an object, which I will call the hour marker, whose position always corresponds to that of the hour hand. It can conveniently be driven from the intermediate shaft of the reduction gearing between the minute and hour hands. The counting object is the rotor, which rotates about the same axis. It starts at the twelve o’clock position and rotates clockwise to the position of the hour marker. It may then continue in the same direction to the starting position, or it may rotate anticlockwise back to the same position. During either the forward or reverse rotation the bell is struck once for each twelfth of a turn of the rotor, between the twelve o’clock and hour marker positions. This gives the correct number of strokes, and ensures that the mechanism is synchronised with the time indicated on the clock.
A “real” clock striking mechanism which has some similarity is described at http://mb.nawcc.org/showwiki.php?title=The_Ingraham_electric_strike_mechanism
Stephen Jeavons’s mechanism
Stephen's mechanism was originally published in the Transvaal Meccano Guild newsletter, but will be more accessible to most readers through the recent article A compact clock-strike mechanism by Stephen Jeavons, Constructor Quarterly 98, December 2012, p26. A feature of the mechanism is its extensive use of Elektrikit parts. At each hour an electric motor rotates the rotor through one full revolution. For each twelfth of this revolution the bell is struck by a hammer actuated by a twelve-lobe cam. When the rotor reaches the hour marker, a contact is made which causes a solenoid to latch the strike arm, thus preventing further strokes for the remainder of the rotor's rotation back to the start position. The striking is re-enabled by a passing strike on the half hour. Photographs and a video of the mechanism can be seen at http://www.nzmeccano.com/image-60018
My striking mechanism
I began working on striking mechanisms in 2011. Independently of Stephen I came up with a solution which also comes into this category but works quite differently. It uses a warning event, at which time the rotor is released and rotates clockwise, propelled by a spring, until it strikes the hour marker. On the hour the rotor rotates anticlockwise back to the twelve o'clock position. Power is applied to the bell shaft, which carries a cam to strike the bell once in each rotation. A simple intermittent motion mechanism rotates the rotor one twelfth of a turn for each rotation of the bell shaft. When the rotor reaches the twelve o'clock position a switch is turned off or a blocking lever is lifted, and the mechanism stops. An article describing two variants of this mechanism in detail, one electrically powered and the other weight- or spring-driven, is Two new striking clock mechanisms by David Couch, Constructor Quarterly 103, March 2014, p20. Videos of the mechanisms can be seen at http://www.nzmeccano.com/image-59445
Phil Ashworth’s mechanism
I have found one other published Meccano mechanism which comes into this category. It is described in An Hour Striking Mechanism by Phil Ashworth, Midlands Meccano Guild Gazette, April 1995, p18. In this mechanism, on the warning event an electric motor rotates the rotor clockwise until it reaches the hour marker position. On the hour, the motor rotates the rotor anticlockwise, back to the twelve o'clock position. In each case the motor is started by an Elektrikit commutator on the minute hand shaft, and stopped by the opening of contacts carried on the rotor. Power is applied to the bell shaft, which operates the hammer only when it rotates in the reverse direction. The bell shaft drives the rotor via 12:1 gearing. Pat Briggs has told me that he saw this mechanism working.
It occurs to me that one drawback of this mechanism is that the warning event will be prolonged and noisy, with the motor running for the same length of time that the striking will later take. By comparison, the warning in a rack and snail mechanism, and in my mechanism described above, is just a single “clunk”.
The word “chiming” has been much misused, and many people take it to mean any sound made by a clock, including striking. In particular it was applied to the No. 2 Clock Kit, perhaps through ignorance or perhaps deliberately by marketing people who thought “chiming” sounded better than “striking”.
Definition of chiming: audibly indicating the quarter hours by playing a different tune, usually on four or more bells, at each quarter. At the hour, chiming is usually followed by striking.
The sound of a chiming and striking clock should be familiar to most people, since the best-known chime, known as the Westminster Chime, is heard on London’s Big Ben and countless public and domestic clocks around the world. YouTube has dozens of videos of chiming and striking clocks. For example, http://www.youtube.com/watch?v=mYBGS6dcmpo
shows the kind of clock that could be found in almost every household up to the nineteen-fifties.
As chiming is so commonly associated with striking, one might have expected that builders of Meccano striking clocks might also turn their attention to chiming. In fact this has very rarely happened. Possible reasons are the lack of suitable bells, a reluctance to use non-Meccano bells, or the lack of the required musical information.
A description of the operation of chiming mechanisms in “real” clocks can be seen at http://mb.nawcc.org/showwiki.php?title=Chime_Clock_Basics&highlight=strike+basics
The Master Clock
As mentioned above, the Master Clock featured in Meccano Magazine, September 1935, p536 includes the Westminster Chime as well as striking. The description includes a rack and snail mechanism with a four-step cam and solenoid-driven hammers, and we are told that “gong tubes” are used. In the photos we can see a group of four Hub Discs which presumably encode the chime melodies. Unfortunately that is all.
My chiming mechanism
I have built a clock which incorporates the electrically powered striking mechanism described above and the Westminster Chime. Suitable bells are readily available, in the form of sets of hand bells, from musical instrument suppliers. I bought a one-octave set and used bells tuned to C, F, G and A. Four hammers are driven mechanically by projections on chime wheels consisting of Hub Discs. The chime wheels are driven by an electric motor and controlled by microswitches operated by the mechanism. Cams on the minute hand shaft start the chiming at each quarter hour, and projections on the rim of the chime wheel stop the chiming when it is complete. This is simpler than the “real” clock mechanism mentioned above.
I showed the clock at Skegex 2013. An article describing the chiming mechanism is A Chiming and Striking Clock by David Couch, Constructor Quarterly 102, December 2013, p54. As far as I know, this is the first published complete description of a Meccano chiming mechanism. A photograph and video of the clock can be seen at http://www.nzmeccano.com/image-59445
Steven Jeavons's Shard Clock
Steven Jeavons has recently built a chiming and striking clock which uses a quartz oscillator and stepper motor to provide accurate timekeeping, and features electrical control of the Westminster Chime and striking. It is described in Shard Clock by Steven Jeavons, Runnymede Meccano Guild Magazine 86, October 2014, p23.
Another kind of audible time indication
A clock which audibly indicates the hour in a way which does not fit the conventional definitions of striking and chiming is described in the article Arnfield Clock with musical chimes by Berco Landman in Constructor Quarterly 84, June 2009, p38. It uses a purchased music box mechanism which plays tunes encoded in punched holes in cardboard strips. Twenty-four such strips are connected in a loop, and the mechanism causes one tune to be played at each hour, following a passing strike.
Another type of audible indication of the quarter hours is known as quarter striking. In its simplest form it consists of a single stroke on the quarter hour, two on the half hour, three on the three-quarter hour and four on the hour. If the quarter strike is followed by a number of strokes indicating the last hour, usually on a different pitched bell, the combination is known as grande sonnerie. I do not know of any Meccano clock that implements quarter striking. A video of a clock with quarter striking built from Fischertechnik can be seen at https://youtu.be/RJSfvf23aXU Here is a challenge for Meccano builders.
Striking clocks in London museums
The clock section of the Science Museum has a mediaeval striking church clock with two large bells, which is now fully operational and fascinating to watch. It produces a quarter strike consisting of two notes, that is one "ding dong" on the quarter hour, two on the half hour and so on. On the hour the quarter strike is followed by normal hour striking. The British Museum also has an old count-wheel clock whose mechanism can be clearly seen in operation.
I am grateful to John Stark for selecting and lending most of the publications quoted here. Thanks also to all those who responded to my appeal in Spanner for information, and to my letters. Thanks to John Stark, Stephen Jeavons, Mike Edkins and William Irwin for comments and corrections.
Matoy (at 11:09pm, Thu 24th Oct, 13)
Congratulation for the first Meccano chiming clock! Yes, i'm one of those who suffered frustration and disappointment on building the No.2 Kit. Also, thank you for your nice review on Meccano striking clocks, as Japan is a desert of Meccano. Wish for your model to be published on MP after appeared in CQ.