Case Studies

Beryllium Copper

Timekeeping Balance Wheel

As an independent watchmaker, David Cottrell maintains a keen eye on metallurgical advances in order to ensure that optimal materials are used in his timepieces. In his search for specialist metallurgical materials, he approached Columbia Metals to obtain some beryllium copper for the production of his balance wheels, a centrally important timekeeping mechanism that functions similarly to the pendulum found in a standing clock, and found today in nearly all mechanical pocket and wristwatches.

The technical advances that have led to beryllium copper’s use for this application are fascinating. David’s interest in the historical development of timekeeping gives him a unique insight into the challenges faced by watchmakers over the course of centuries.

“During the development of highly accurate timekeepers in the 18th and 19th centuries, one of the biggest challenges was to devise a system that would compensate for variations in time keeping  due to changes in temperature,” begins David. “Whilst the implementation of a balance spring had dramatically improved overall accuracy, changes in temperature would nonetheless continue to affect the timing of the watch as a result of the expansion or contraction of the metal used for these key components.  For most applications, the changes in the mechanical properties of a metal at normal everyday temperatures can be ignored; however, when a balance spring is vibrating at 18,000 times per hour, even the smallest changes in elasticity can quickly mount up.”

“Since the balance spring is used to control the rate at which the balance oscillates, the effect of changes in the balance itself also has an impact,” continues David. “Here, small changes must be taken into account, with the balance expanding and contracting under the influence of higher and lower temperatures. The result is that this expansion and contraction alters the radius of the balance’s gyration and therefore its period of vibration. As a result, to achieve optimal chronometric results, the spring and balance must ideally be treated as a matched pair, if any degree of accuracy is to be expected from the watch.”

“Due to the limited material technology at the time various compensation mechanisms were devised to cancel out these small variations. These included the ability to vary the attachment point of the spring (and thereby its effective length) together with a wide range of compensating balances, notably those designed by John Arnold.”

“Eventually, advances in metallurgy provided a solution with the introduction of balance springs with a reduced sensitivity to thermal change such as Isoval, Nispan-C and Nivarox.  It was found that by pairing balance springs made of these materials together with balance wheels machined from non-magnetic and highly corrosion resistant beryllium copper, variations as a result of thermal change in this essential area of the watch’s movement were essentially nullified.”

As an independent watchmaker in the English tradition, David has highly specific and stringent requirements. “Obtaining small quantities of relatively exotic materials can be quite challenging,” concludes David. “However, Columbia Metals were extremely helpful and pleased to supply me with a 300mm length of beryllium copper bar that will be sufficient for the production of a number of my timepieces.”

About David Cottrell
Working from his small yet very well-equipped workshop in Somerset, David Cottrell is a rare breed of independent watchmaker able to create truly handmade and exceptional timepieces. All the parts of the watch are designed and made in the workshop using traditional methods without the use of computerized machining processes.

From the simplest screw through to the complex co-axial escapement as well as the case, dial and hands, all receive the same close attention to detail during manufacture followed by extensive hand-finishing – all executed by a single individual. As traditional machines have become more and more difficult to source, David’s extensive background in toolmaking is an invaluable asset, allowing him to design and make his own horological tooling as required for each timepiece.

While currently focused on making pocketwatches, David is in the early stages of development of a design for a wristwatch. Further examples of his craftsmanship and beautiful timepieces can be found on his Instagram page.

About beryllium copper
Beryllium copper is an alloy capable of achieving the highest strength and hardness of any commercially available copper alloy. With approximately 2% beryllium content, it is particularly well suited for machining into intricate shapes. Columbia Metals stock beryllium copper in round bar from 3/8” to 4” diameter.

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