Friction
There once was a time, when it took about five minutes to figure out how to start a fire. A sheltered place must be found where a dry stick is frantically rolled between the hands to drill a hole in a piece of dry wood held under the feet. If all went well then no hole was made but smoke appeared, a few sparks flew up and the fine "wood-wool" that was placed around the "drilling place" ignited. Utterly simple. Nowadays, hardly anyone does it that way. But the astonishing thing about this story is that these fire spitting drill-holes are to be found in every watch. Wherever friction occurs heat is generated and thus friction is the secret of making a fire. Wood is rubbed on top of wood and becomes warm. If done skilfully it gets so warm that it will start a fire because friction causes heat but friction will occur everywhere where two surfaces are moved against each other. For example in a watch these are the pivots in their bearings, the wheels engaging the pinions, the pallets of the escapement against the teeth of the escape wheel, the winding up of the mainspring coils against each other and so on. Of course none of these warm friction points are able to ignite a fire but nevertheless warmth is produced. And inside the watch it means that driven energy is changed or rather is lost before it reaches the balance. What is lost here can be regarded as lost energy.
Energy
Because watches are so small, an endless amount of energy cannot be stored inside and of course because friction is equated with wear, horologists try to keep the amount of lost energy as low as possible by minimising the condition of friction. Here the advantage is that a lot of energy can be "pumped" into the balance spring, which makes it insensitive against attacks from the outside e.g. against knocks.
Material
But how to minimise friction?
One way would be via the material that rubs. But two parts are needed to rub against each other when we talk about a combination of materials. Roughly speaking, there are only two of them throughout the world of horology. (Hardened) steel with brass and (hardened) steel with ruby. The two pairs undeniably develop so little friction that no fire can start!
Surface
The next thing is the surface. The smoother the surface of the contact areas, the less friction is caused. Obviously!
Oil
Well greased runs better. It is the same with watches. To reduce friction considerably it is enough to add only a touch of oil.
The years
But now it starts. Oil gets old! It ages because of its chemical composition, changes because it gets dirty from wear, attacked by bacteria and so on..., or it just disappears (it creeps away). This means that the condition of friction worsens, hence the balance gets less energy and its amplitude reduces. The balance now gets more sensitive when disturbed (bumps, knocks and so on) and the watch doesn't run accurately anymore. A contradiction!What to do?
Lecturing horologists have been preaching for centuries that watches must be cleaned and oiled regularly. This is to ensure that the oil doesn't get too old and is used for only the period during which it demonstrates a useful lubrication capacity. A hundred years ago maintenance intervals were 2-3 years but today it lies between 3-5 years. But changing the oil in good time is not enough for the very accurate timekeepers. Marine chronometers especially were driven to the epitome of what is possible. After all, they were responsible for the lives of many seamen who depended on their navigational precision. Therefore escapements were invented that didn't need any oil. A brilliant idea, as the oil at the escapement represents a very critical influence over timekeeping accuracy. Critical, because very little energy must be transmitted as consistently as possible.
A Chronometer Escapement for the wrist
These oil-free escapements, brilliant as they may be - very particularly in marine chronometers - could never show their capabilities properly in watches because they couldn't accommodate the harsh environmental influences like bumps and knocks. The marine chronometer escapement is missing a few simple characteristics which are quite important for watches. For example two teeth of the escape-wheel can pass instead of one causing the escapement to trip. Furthermore, a watch with a chronometer escapement does not start by itself. It seems as though this fact was a thorn in the side of George Daniels because he has constructed an escapement that promises more. No oil, it starts by itself, a safeguard against the tripping and an impulse at each vibration. All of this is so promising that nowadays it has become standard in some watches. You may now ask, what about the oil? Well, time will definitely answer this question. Let's wait another 5 - 10 years. |
