A Contemporary Clock

In late 1998 I set out to design and build a Glasglocken-Spieluhr of my own. The first step was a careful study of the works by Claude Reeve,(1) Donald De Carle,(2) and Karl Kochmann.(3,4) These give good insight into how musical, chiming, and flute clocks work.

• The following features were decided upon.
• Ten-day running with a one-second beat pendulum.
• Weight driven.
• Recoil escapement with a brass escapement wheel.
• Key winding.
• Striking control with a rack and snail.
• Gears held between plates.
• Music train mounted independently behind the time and striking trains.
• A single melody playing each hour on glass bells.
• Animation.

Design work progressed through a series of gear count calculations, working sketches, and full size gear layout drawings.

All wheels and pinions in the clock are laminated from quarter-sawn 0.1 inch Australian blackwood (Acacia melanoxylon). Lamination is used to provide better dimensional stability to changing humidity and to give strength to the gear teeth.(5, 6) Veneers are glued with epoxy resin, and their grains run at right angles to one another. Wheels are made from 3-ply. Pinions are made from 7-ply, except for the first pinion in each gear train. These must be particularly strong and are lantern pinions with steel trundles and brass shrouds. Wheel teeth were cut with a piercing saw and finished by filing and sanding. Teeth of just under 0.2 inches pitch are the finest that I can hand cut in wood and this determined the diameter of each wheel. All wheels except the great wheels are crossed out. Steel wire runs through the length of each wooden arbor, and the pivots turn in pieces of brass set into the wooden plates. The brass pieces are bushed with hard brass clock bushings. All of the plates are 0.35 in. commercial 5-ply.

Work started on the music barrel and music gear train. The barrel is made from twelve staves of Australian blackwood and is 5.4 inches in diameter, 8.4 inches long, and weighs 1 lb. 4 oz. Care was taken to make it perfectly round and well balanced. The music barrel turns once each hour and must turn 240 times in 10 days. The gear count allows the drum to turn 243 times before the weight line has completely unwound. The weight drops about 55 inches in 10 days.

The music train is held between three plates. The right and center plates measure 9.8 in. W x 11.2 in. H, and the left plate is 6.1 in. W x 11.2 in. H. The gear work is mounted between the right and center plates. The music barrel spans a cut-out piece in the center plate and pivots in the left and right plates (Figures 1 and 2). Six turned pillars hold the right and center plates 4.1 in. apart, and five pillars hold the left and right plates 9.8 in. apart. A lever on the outside of the right plate controls the rotation of the music barrel and the locking of the music train (Figure 3). The lever is pivoted near one end and a tail at the other end drops into a notch on a count cam wheel. This wheel is carried on the pivot of the third wheel. A small finger extends down from the lever between the pivot and tail. This locks the music train by engaging in a notch on a locking cam wheel. This wheel is carried on the pivot of the fourth wheel. The music barrel revolves once when the music train is unlocked. The train is re-locked by the tail and finger of the lever dropping back into the notches in the count and locking cam wheels. Music can be silenced by turning a hand on a small dial mounted on the right plate. When the hand is turned a detent is locked in the path of the pin on the warning wheel thus locking the gear train. The music train is wound with a cranked key by turning a winding square that protrudes through the right plate (Figure 4). The same key fits the time and strike trains.

A carillon of eight bells hangs in a rack above the music work (Figures 5 and 6). A keyboard is mounted over the music barrel, and the music is transferred through wire rods and small wooden rollers to the bell hammers. The keys are brass. Each key has an adjusting screw above its tail that controls the amount that the key is raised by the music barrel pins. The bell hammers fall by gravity. They have a wooden head with a small lead weight attached above to give a crisp hammer action. Each hour, before striking, the clock plays the first eight bars of the Australian folk song “Waltzing Matilda.” The music lasts for a quarter of a minute and is of pleasing quality. The drive weight and size of the fly vanes were adjusted so that the music plays at a moderate tempo. The music train is driven with a weight of 16 lb.

I am not a musician, so I had the help of a skillful local instrument maker. He was able to tune the glass bells, arrange the music, and mark the 61 pin positions on a paper grid so that I could pin the music barrel.1 It was something that neither Peter Biffin nor I had done before. Together we visited local stores and selected eight lead crystal glasses that we ground to give the octave range that the music required. About 60 glasses were tested to find eight suitable for tuning. Lead crystal glasses were used because of their pleasing tonal quality and also because they can be ground more quickly than ordinary glass. A local glazier kindly allowed us to use his water-cooled Carborundum™ belt to do the grinding. We used a new 240 grit belt, and I carefully ground the rim of each glass while Peter constantly checked the pitch. All of the glasses required some grinding, except for a red wine glass that was used for the lowest note. The grinding and tuning took about three hours to complete. Some glasses required more grinding than others. A trial grinding of a white wine glass removed just over 0.4 inches in an hour and raised its pitch by about 380 cents. There are 1200 cents in an octave.

Finally, the stems were cut off and ground smooth. A short section of stem was left to hang the bell in the rack slot. The bells are well secured so that they do not move in the rack. This was done by gluing suede leather around the stem and packing Blu.Tack™ that had been colored with wood stain around the pud.

The details of the time train and the motion work are shown in Figures 6 and 7. The pivot of the third wheel extends through the back plate and carries a lifting cam. The cam is secured to the pivot with a grub screw. Every hour the cam raises a lever that is pivoted on the back plate. This lever is linked to the music train. As the cam lifts the lever the music train is unlocked and held on warning for about two minutes. At about half a minute before the hour the lever drops and the music plays. The weight driving the time train weighs 17 lb. and drops about 39 inches in 10 days.

Hear the glass bells (444 kb .wav file)

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