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Blog: Is it Balance or “Balance Wheel”?

Copyright © David Boettcher 2005 - 2024 all rights reserved.

First published: 18 June 2024, last updated 18 June 2024.

I make additions and corrections to this web site frequently but, because they are buried somewhere on one of the pages, the changes are not very noticeable. I decided to create this blog to highlight new material.

The article below is not part of any page, it's just some thoughts on terminology.

As always, if you have any comments or questions, please don't hesitate to get in touch via my Contact Me page. I would be interested to get your feedback on this article, about how it reads and if there are any mistakes!


Balance or "Balance Wheel"?

At the heart of a watch are the balance and balance spring. These form the resonant oscillator that enables the watch to keep time. Some people call the balance a “balance wheel,” a term commonly used in the American watch industry. While I have no objection to this — people are free to use whatever term they like — I prefer the term “balance.” Those new to watchmaking who stumble across my website might wonder why, so here I explain the reasons.

Despite my German family name, I am English and prefer to use traditional English watchmaking terms. In English watchmaking, watch wheels are part of the train that transmits power from the mainspring to the escapement. Therefore, watch wheels are strictly round and have teeth around their outer edge to drive a pinion.

Watch balances do not fit the description of a watch wheel. Although balances are often round, they do not have to be — a balance can be almost any shape — and they never have teeth on their rims. Let's delve into this in more detail.

Balances

The first mechanical timekeepers had a balance consisting of a horizontal bar with mounted masses that could be moved towards or away from the centre of rotation to alter the moment of inertia, thereby changing the rate. The origin of the name “balance” is unknown; it may have arisen because the bar with its suspended masses somewhat resembles a merchant's balance used for weighing goods, or it might simply be that the bar had to be in balance, with the masses at equal distances from the centre, for the clock to work.

The first small, portable timepieces that could be worn — and therefore described as watches — were made in the sixteenth century, either in Germany by Peter Henlein or in northern Italy. In German, a balance is called an “unruh” or unrest, due to its never-resting motion. In Italian, it is called a “volante.” In French, the balance is called a “balancier,” which in English is “balance.” The term migrated across the channel to England with French watchmakers, most notably Huguenot refugees from France in the seventeenth century, although smaller numbers had been coming to England for many years by then.

The balance of a watch must be as light as possible to minimize stress on the balance staff pivots, which are made very fine to reduce friction in their bearings. Additionally, making the balance lighter will reduce the change in friction that occurs between the lying and hanging positions. The balance must also store as much energy as possible, which requires a large moment of inertia and implies a heavy balance. A simple bar balance achieves neither of these objectives, as it has too little of its mass at the outer ends, giving it a low moment of inertia for its mass. Making a balance in the form of a disc would be an improvement, but it would still have a lot of its mass toward the centre, where it is not very effective.

The ideal solution for the restricted space available in a watch is a balance that is as large in diameter as possible, with light arms and a heavy circular rim, so that the majority of its mass is concentrated at the maximum distance from the centre. However, there is no requirement for the rim to be continuous. A compensation balance has a rim that is cut to allow the sections to curl inwards and outwards in response to changes in temperature.

Although the ideal balance has its mass distributed in a circle as far as possible from the centre of rotation, this is not a reason to call it a wheel, a term that in watchmaking has a very specific meaning.

The original balances, simple horizontal bars with masses placed along their length to regulate timekeeping, were clearly not wheels. Balances like these were also sometimes used in marine chronometers. Although an ideal balance has the majority of its mass concentrated in a circle, the rim does not have to be continuous. A compensation balance, which has cut bimetallic rims, is clearly not a wheel, and neither is an ovalising balance used in some watches, most notably the Hamilton Model 21 marine chronometer.

Now that you have read this discussion, I hope that you too will prefer the term balance. The word “wheel” is really unnecessary in this context, everyone understands what is meant by “balance” alone, and you save a space and five characters each time!

Balance Springs

Nemo 1879
Nemo 1879: Click image to enlarge

The English scientist Dr. Robert Hooke was the first to observe that the restoring force produced by a spring is proportional to the degree to which it is extended or deflected, resulting in his famous law “ut tensio, sic vis” (as the extension, so the force).

Around 1658, Hooke had the idea that applying a spring to the balance of a watch would improve its timekeeping by making the period of its oscillations consistent. Hooke sought sponsors for a patent application, which was drafted, but the work was interrupted by the Great Fire of London, among many other demands on Hooke's time.

Hooke's idea, although not the details of his design, was communicated to Christiaan Huygens who, nearly 20 years after Hooke had the idea, conceived the spiral balance spring in 1675. He announced this as his invention, much to Hooke's great annoyance.

In English watchmaking, the spring applied to the balance is called the balance spring, or simply the spring if the context allows. I am aware that there is another term used for this spring, but it is not one that I use. In the Horological Journal in 1879, a letter from someone calling themselves Nemo explains why. In British English, the alternative term is regarded by old-fashioned writers such as myself as being rather distasteful.

It should be noted that the translators of Saunier's Modern Horology from French into English took note of the objection to the alternative term by Nemo and others, and from then on consistently translated all instances of the French “spiral” into the English “balance spring”.

If you have any comments or questions, please don't hesitate to get in touch via my Contact Me page.

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Copyright © David Boettcher 2005 - 2024 all rights reserved. This page updated June 2024. W3CMVS. Back to the top of the page.