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The taming of the screw

The taming of the screw

Tuesday, 06 December 2016
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Vincent Daveau
Journalist, watchmaker and historian

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However insignificant it may appear on the surface, you would need to have a screw loose not to give this fundamental part the attention it deserves. The screw, whose invention is lost in the convolutions of history, performs most of the mechanical connections in today’s complex calibres. Whoever said screws matter hit the nail on the head.

G.-A. Berner’s dictionary of watchmaking defines the screw thus: “Device used for fixing or assembling. Screws usually have the following parts: the shank, wholly or partly threaded, and the head which has a slot to take the screwdriver.”

Which doesn’t help us much, truth be told. It is worth noting that the screw – a mechanical piece that uses a helical surface to hold two elements together – appeared in both watchmaking and armoury in the early Renaissance period, thus roughly coinciding with the spiral-shaped blade, or spring, that gave us our first watches. Until nineteenth-century industrialisation, there was no standard screw thread. Each watchmaker would make his own screws, hence why today’s restorers must have at hand a palette of taps, dies and what look like tiny cake servers (and which are in fact screw plates), which they use to make replacement screws and other missing components.

The majority of screws in old watches are fire-blued. © Vincent Daveau

One of the first things you learn when studying watchmaking is that screws have a marginal propensity to “do a runner” at the first slip of the hand, and that it is virtually impossible to bring them out of hiding, even with a magnet. Joke aside, is there anything more twisted than a screw, with its sharp corners and multiple sides. Fail to get a good grip with the tip of your tweezers and the offending object is guaranteed to go flying through the air, leaving you on all fours under the workbench. As if that weren’t enough, watchmakers like nothing more than to use screws of varying lengths and sizes, which is their special way of keeping repair staff on their toes. Hence the importance of identifying each one and memorising their position on the plate or bridges.

Louis Vuitton
© Louis Vuitton
Order and method

Some screws have a distinctive shape and correspond to a particular purpose, which somewhat facilitates matters. But be warned, keeping them in order is no less a complex task even for an experienced craftsman, who will systematically sort them into different categories. Because nothing looks more like a screw than another screw. To prevent disaster, master watchmakers of yore invented a way to identify screws with a left-hand thread: often used for the barrel ratchet, they have a line on each side of the slot where the screwdriver fits. As for the others… they all look the same. Good luck with that!

The majority of screws in old watches are fire-blued, a sure sign for restorers that they are in tempered steel.

Amateurs reading these lines will note that the vast majority of screws are made out of steel which most of the time has been quenched and tempered. This ensures a balance of ductility and hardness so that the screw will not twist out of shape when tightened, nor break like glass if excessive stress is applied to the metal. One of the reasons the heads on old screws sometimes snap off is inadequate heat treatment. This can have serious consequences: retrieving the threaded shank from a brass or gold component or plate is no easy task.

In addition, the majority of screws in old watches are fire-blued, a sure sign for restorers that they are in tempered steel. This colouring, which goes from a deep blueberry purple to strong, shiny black, is a lasting treatment which also provides a certain amount of protection against corrosion due to humidity. As in the past, some leading Manufactures still fire-blue certain of their screws. On a fire-blued screw, even the slot is coloured, which isn’t generally the case when a screw has been chemically blued by electrolysis, to save time and money.

Richard Mille
© Richard Mille

In this world of the infinitely small, strict rules must be obeyed. A screw destined to take its place in a quality watch must conform to precise aesthetic criteria. As the master George Daniels points out in his reference work, Watchmaking, “at one time screw slots were always bevelled at the edges to prevent marking but nowadays, probably in the interest of economy, the practice is almost discontinued. When making new screws the watchmaker can include this necessary refinement merely by the stroke of a file and the screws will retain their new appearance no matter how many times they are turned.”

Richard Mille RM 50-02 Tourbillon Split-Seconds Chronograph
Richard Mille RM 50-02 Tourbillon Split-Seconds Chronograph
Original down to the screws

In recent years, some brands have developed screws for their own use, which in turn imply special screwdrivers to tighten and loosen them. Some are simply hollow hex screws of the type used on car cylinder heads or on the crankcase of a sports bike. Others have two or three tiny holes where the slot would normally be. The advantage of these constructions is that the screwdriver blade cannot slip and scratch the surrounding metal; they do, however, oblige the repairer to have the appropriate blade with which to open the case or remove the component. Now we know how the mechanic feels when he has to take the wheel rim off a sports car and doesn’t have the right tool to loosen the “anti-theft” device.

F.P Journe Perpetual Calendar
F.P Journe Perpetual Calendar

François-Paul Journe was among the first contemporary watchmakers to use special screws for his watch cases. He was joined by Richard Mille, who looked to Formula 1 racing for inspiration. Since then, other brands have come up with their own distinctive designs. They include Hublot, with its H-shaped slots, and Oris which equips certain of its sport watches with screws that have a Y-shaped slot. In contrast, several brands associated with contemporary designs and original calibres prefer screws which are visually inspired by traditional styles, rather than the original treatments one might expect. Others have opted for standard screws to attach the back to the middle of their otherwise futuristic cases, when in-house screws would add the finishing touch and give only authorised repairers the possibility to delve into the heart of the watch.

Hublot Big Bang Meca-10
Hublot Big Bang Meca-10

Let’s hope to see more brands turn their attention to this tiny component, and propose forms and finishes beyond the usual fare. Watch this space!

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