East Midlands branch visit

27 August 2014

On 19 March the IOP East Midlands branch visited the John Taylor Bellfoundry in Loughborough.

The John Taylor Bellfoundry

John Taylor & Company can trace their history all the way back to the 14th century. Some traditional casting methods still stand the test of time, while some new technology aids machining, handling and tuning of a vast range of bells.

The bells manufactured on this site range from small hand bells to some of the largest in the world, such as Great Paul, weighing in at just over 17 metric tonnes, cast in 1881 and installed at St Paul’s Cathedral in London. All bells, wheels and frames are custom-made.

We spent around 90 minutes on the tour through the engineering works, across the road into the foundry via the wood shop and the tuning room. There were several discrete manufacturing areas:

Patternmaking – Apart from wooden patterns, and a special sand for casting, the core and mould are bound by a mixture of bricks, loam, goat hair and horse manure; lovely. Sometimes the old ways, albeit bizarre, are not replaced by modern technology. Each bell is individually cast in its own mould and therefore unique. It is cast close to its final size, so that the minimum of machining and fettling is required.

Casting – Most of the bells are cast from an especially malleable bronze that has the correct mechanical characteristics to make it resound for an extended time after being struck. The alloy used is something of a trade secret and part of Taylor’s established intellectual property.

Final Machining & Tuning – A visit to the tuning room revealed that some science and mathematics were behind the tonality of the bells. The type of material used has a lot to do with the ring or the “clank” in some cases. Then the shape of the bell has a lot to do with the resonant frequencies set up and its ability to radiate its sound into the far-field. During final tuning the bells are subjected to a complicated tuning procedure utilising a method that detects and optimises five musical notes based on the strike frequency “f=n”:

  1. Hum, f=n/2
  2. Prime (strike note), f=n
  3. Tierce, f=6/5n (normally a minor third above prime)
  4. Quint, f=3/2n (perfect fifth above prime)
  5. Nominal, f=2n (the highest discernable note from the bell)

 

The interior of the bell is machined and finely tuned to balance the characteristics of the sound around these five musical notes. Adjustments made to the internal profile affect all notes to some degree. It’s a five-dimensional balancing act that requires unique knowledge and a feel for what material to remove. The process is far more than meets the ear.

Other processes – The wood shop also manufactures bell wheels. There was a rope room (that we didn’t see on the day) and a large fabrication facility on the shop floor to manufacture the frames, clamps and accessories necessary for hanging the bell in its final place.

We received a demonstration of ringing a bell and using the bell wheel to slow and even stop the bell at the top of swing, so it only rings once per rope pull. A set of mechanical stops is adjusted so that the timing delay between “pull” and “ring” can be mastered by the operator. Each bell would have its own delay time, and “ringing the changes” requires very complicated and skilful practice.

Finally, some of the phraseology used in this report is from a lay person who knew little of bells before this very interesting tour of history, technology and the unusual uses of horse manure. I hope that this ignorance hasn’t detracted from capturing the flavour of this remarkable place. Well worth a visit if you are in the Loughborough area.

Mike Swanwick CEng MInstP