chronograph-history-4

The Column Wheel Chronograph- Introducing the Longines Manufacture Calibre L688.2

I mentioned in my post about the ETA 7750 that I would soon be servicing the Longines L688.2, its based on the latter but has been re engineered to include a column wheel based chronograph instead of the usual cam and lever system. I thought I would take the chance to not only write about the Longines and show its assembly but also compare the column wheel and cam/lever chronograph systems. The column wheel system is more common in high end chronograph watches due to the extra costs involved in its manufacture.

The Swatch groups desire to push the Omega brand towards the higher end of the market has enabled Longines, once a great brand, to start to move into the territory once occupied by its stablemate. The start of this renaissance began when Longines enlisted another one of its stablemates, the movement manufacturer ETA, to develop an exclusive column wheel chronograph movement to be used in its high end models. ETA developed the movement known as the A08.231 from the basis of the vulnerable 7750, the basic movement up until the chronograph is identical but from this point onwards some parts are completely new. The decision to use the 7750 as a base for this new calibre must have been as easy choice for ETA to make because its a calibre thats reliability and durability has been proven over a number of decades. The cost savings from this decision would have also been rather large, an important factor when you consider the relatively low price tags of the watches that this movement was developed for.

The movement was launched by Longines in 2009 and has become the focal point of their top of the line models. The development brief for this movement was to create a column wheel chronograph that was easy to use and most importantly affordable. The column wheel system that was designed by ETA’s engineers, is exceptionally user-friendly for a mechanical chronograph, requiring only the finest touch to start and stop the mechanism and to reset the hands to zero. The blued steel column wheel is nice touch that along with the decorated bridges bring an air of quality to a movement that is often seen through a sapphire case back.

The L688.2 (A08.231)…

chrono-roue_colonnes-mvt-1

The chronograph is an instrument used to measure intervals of time and the idea of its existence can be traced back to the late 17th century. The first chronograph designs emerged in the 18th century and production began in the early 19th century. These early designs however had a major flaw, when the reset button on the chronograph was pressed whilst the chronograph was still running, the gear train would instantly move and major damage was caused to the mechanism. In order prevent this accidental damage by the operator, a safety mechanism was later to developed in the form of a column wheel (Sometimes called a castle wheel due to its appearance). The column wheel is a large wheel that has a number of triangular teeth that sit vertically on its top surface, the wheel is turned by a series of levers that are connected to the chronograph buttons. When the operator pushes one of the buttons, the column wheel turns and activates the chronograph functions in a specific order, which is start, stop and reset. If an incorrect button is pushed at the wrong time, the column wheel doesn’t engage and the once inevitable damage is prevented. The column wheel became one of the most popular forms of chronograph system, the purists choice due to its smooth action and the huge levels of skill it required to manufacture.

The L688.2 column wheel…

chronograph-history-4

Column wheel movements were generally expensive to produce because they required precisely made parts in order to function correctly. For this reason, inexpensive mass-produced chronograph movements just didn’t exist. In order to bring mechanical chronographs to the masses, simpler systems, at least when compared with the column wheel, were introduced. By far the most popular of these alternatives was the cam and lever (coulisse) system. Essentially the column wheel is replaced with a series of levers that mesh together with an eccentric cam. This makes adjustment and repair a much simpler task, production costs are also dramatically reduced due to the fact that manufacturing tolerances can be much bigger. Although in basic terms they are not really any worse than a column wheel chronograph in terms of function, they are often seen as inferior, try naming a high end chronograph movement that doesn’t use a column wheel? There aren’t any that I can think of…

So to a question most of you might ask, how exactly does a basic chronograph movement work? Let me try and explain. In the case of a cam and lever 7750, a  small oscillating pinion driven by the seconds wheel of the base movement is part of a movable arm which sits adjacent to the central chronograph wheel. When the chronograph is engaged, the arm carrying the oscillating pinion is moved so that it meshes with the central chronograph wheel. It begins turning the chronograph wheel which it turn moves the minute counter wheel. When the chronograph is stopped, the oscillating pinion is moved disengaged from the central chronograph wheel and a brake is applied to the wheels. Pushing reset engages a series of spring-loaded hammers that push everything back to their starting positions and the chronograph hands back to their zero positions. Other systems work slightly differently but the principles are the same.

The central chronograph wheel normally has very fine teeth to ensure it meshes well with oscillating pinion in order to eliminate it skipping or breaking teeth. Despite this, it isn’t perfect and you can sometimes see the central chronograph seconds hand jump slightly when the chronograph starts. This is because a stationary wheel is hitting a moving one, some chronographs can have a degree of imprecision because of this, its possible for the hand to move as much as half a second. That doesn’t sound like a huge problem but in precision timing thats a lot. Due to the nature of there action, these wheels can wear heavily over time if the chronograph is used constantly. A solution to this was developed in the form of the vertical clutch system.

This system allows the wheels to be in mesh constantly, the clutch engages or disengages the mechanism as required. Usually amplitude is lost on a traditional chronograph when the chronograph is started due to the increased friction caused by having to drive the chronograph wheels. Due to the wheels being constantly driven when a vertical clutch is used, amplitude often increases when the chronograph is started because the friction of the clutch is released. The vertical clutch  has a pinion running through its centre, when the chronograph isn’t running the clutch is held together but when the chronograph is running, the clutch is allowed to separate and the pinion is able to turn. Vertical clutches are expensive to produce and can’t be repaired so they are normally only seen in the finest of chronograph movements. However in recent times, the number of manufacturers choosing to use them has risen significantly.

A vertical clutch…

ml_image.614106

Anyway, lets get back to the Longines,  as I mentioned previously, the movement is exactly the same up to the chronograph mechanism but differs in some areas from this point onwards. There are a few pictures below showing the basic movement minus chronograph mechanism being assembled. I will also try and explain to you how the chronograph mechanism in this movement works with a helpful link to the Longines website.

The starting point…

IMG_3965

Barrel in place…

IMG_3983

Followed by the train wheels and balance stop….

IMG_3981

And the bridge…

IMG_3986

The screws are fitted and tightened…

IMG_3989

Lubrication applied for the crown wheel…

IMG_3999

Crown wheel fitted…

IMG_4004

Lubrication applied for the crown wheel core…

IMG_4008

Crown wheel core fitted…

IMG_4010

The movement is turned over…

IMG_4012

The winding stem, winding pinion and sliding pinion are fitted…

IMG_4015

The yoke spring goes in next…

IMG_4016

Followed by the rocking bar, setting lever and yoke…

IMG_4018

And finally the setting wheel, intermediate setting wheel and the setting lever jumper…

IMG_4023

The movement is turned over and the pallets are fitted…

IMG_4026

Followed by the balance…

IMG_4027

As you will have noticed, the movement up to this point is identical to a standard 7750 but as the chronograph parts are fitted you will see a number of new parts that are exclusive to this calibre. Unfortunately I wasn’t able to take any pictures of the chronograph mechanism due to time constraints and with the technical information currently not available to anyone other than Longines accredited repairers, the best picture I can come up with is a partially exploded diagram from which some of these new parts can be spotted.

L688.2 Chronograph mechanism…

Screen Shot 2013-03-29 at 14

The most obvious of these new parts, mainly due to its blued steel appearance, is the column wheel which replaces the standard 7750’s cam. The chronograph levers are also new and are required for the change in system from the cam and lever to the column wheel. They operate in a similar way but they are operated through engagement with the columns on the column wheel. This system tends to be smoother in operation due to the controlled and precise movement of the column wheel which is moved by a much shorter operating lever.

A link to how it works courtesy of Longines themselves…

http://www.longines.com/virtual-catalogue/Longines-Info-Column-Wheel-2011/index.html

I thought I would simplify the description a little to make it a little easier to understand. The first diagram at the link above shows the mechanism in action, when the push button (A) is pressed, the operating lever (B) moves the column wheel in a clockwise direction by one notch, the resulting action moves the clutch-rocker (C), which carries a stud at one end, with the stud clear, the clutch can move and engage the oscillating pinion (D) with the central chronograph wheel.

The second diagram at the link above shows the chronograph mechanism stopped, once again pusher (A) is pressed, which causes the operating lever to move the column wheel by one notch, the resulting action moves the clutch-rocker in an anticlockwise direction, which in turn engages its pin (B) with the clutch once again, the result is that the oscillating pinion (C) is pulled out of engagement with the central chronograph wheel and two brakes are applied to stop the chronograph wheels.

The last diagram shows the chronograph mechanism being reset, when the push button (A) is pressed, a hammer (B) is applied to the three heart cams positioned on the chronograph wheels, these wheels can rotate in either direction until the flat section of their cam rests against the tips of the hammer (in turn reseting the hands), the flyback yoke (C) actions the hammer that controls the chronograph hand and the minute counter, the beak (D) is driven in between two columns of the column wheel when the pusher (A) is pressed, its this beak that prevents damage to the mechanism by preventing the reset process from happening if the chronograph hasn’t been stopped. If the chronograph hasn’t been stopped the beak (D) directly hits a column on the column wheel and prevents the reset process taking place.

So which system is better, Cam and lever or column wheel? Well, generally most expert opinions state that the column wheel wins hands down for a few reasons. The first due to its smoother pusher action which is a result of the column wheel having less play between itself and the hammers. The second reason is dependant on whether the column wheel is used in conjunction with a vertical clutch, with this combination the amplitude remains virtually the same whether the chronograph is on or off, this is due to the chronograph mechanism being constantly driven. The time keeping difference between chronograph on and off is minimal as a result. Although in my opinion there isn’t too much difference in how they work and feel in use, I think the column wheel system is definitely superior when its used in conjunction with a vertical clutch. The column wheel itself is also more appealing from an aesthetic point of view in comparison to a cam. From a watchmakers servicing point of view, there is a little difference between the two systems in terms of time required to service and difficulties encountered along the way although when a vertical clutch is used there is one slight issue. I’ll cover this in my next chronograph instalment which takes an in depth look at  a Frederic Piguet movement that has both a column wheel and a vertical clutch. Thanks for reading once again.

 

Posted in The British School of Watchmaking and tagged , , , , , , , .