“Let’s repurpose the wheel, but not reinvent the axle” was our approach. This was not a specific reference to the mechanics in the watch movement, but our philosophy to develop our movement. By wheel, we mean our innovative way to display time, and by axle, we mean the basic movement that keeps time.
The SNGLRTY time display has a certain familiarity, with the hour hand rotating once every 12 hours. This speed has been natural to us all since single hand clocks maintained time on church towers. The twist is that the hour hand simultaneously indicates the minute in its large circular aperture. This way, the minutes are shown continuously and colocated with the location of the hours. To achieve this minute display, the minutes rotate counterclockwise on a disc printed with the 60-minute scale over 360°. This minute disc rotates coaxially around the center axis of the watch movement.
The minutes run counterclockwise, and the hours moving clockwise, yet both share the same path. This results in the two indicators, hours and minutes, converging at more than 360 degrees per hour, measured from the hour hand. Therefore, for the correct minute to be displayed concurrently with the location of the hour hand, one of the rotating indicators (hour or minutes) must run slower than on a typical two-hand watch.
The Rhythm Of The Hour Hand Dates Back Centuries
We understood the centuries-old intuitive readability of the hour hand. This structure started to develop with the advent of sundials with the early Egyptians. We can orientate ourselves in time by the position of the hour hand with a glance. Our desire was to maintain that connection, so we focused on manipulating the speed of the minute display and slowing it down.
Into The Details
Two specific changes had to happen for our movement to work:
Complication 1 – the minute disk should move counterclockwise.
Complication 2 – The speed of the counterclockwise rotating minute disc must slow by 1/12.
There is no standard solution for this in the market. If there had been a solution in the market, then I doubt we would have received a patent! With no movement in the market that provides these functions, it was up to us to create it.
Key Decisions Along The Way
This is where Steve and I decided not to reinvent the wheel. Instead, we decided to start with a well-established tractor movement and amend it for our purposes. The tractor movement would provide the primary time-keeping function, and we would amend it to display our complications. This is a well-worn path for many famous watch companies.
The mechanical changes are generally added to the top of the tractor movement and are called a complication plate or a module. All the energy is transmitted to the complication plate. Hence its name, the tractor movement, because it powers the additional functions of a watch.
Together with the watch engineers from Le Cercle des Horlogers, we agreed that the addition of the complication plate should impact the tractor movement as little as possible. We wanted to focus on the result; there was no need for us to question or reinvent the driver behind our time display.
Small Decisions, Big Implications
Another decision we made was that the SNGLRTY time display should have a center second indication. This decision allowed us to select two tractor units we would affix with our complication plate. We decided to use Sellita movements to ensure supply plus their movements are well established in the market.
Our engineers designed the complication plate so that we can assemble it directly on the tractor movement. The complication plate is attached to the tractor movement like a classic dial. Our complication plate has feet like a standard dial; these feet are inserted into the tractor movement to hold the complication plate in place. The advantage of this attachment method is that there is no need to adjust any aspect of the tractor movement.
For commercially available movements many aspects can be configured at the point of purchase. One aspect that is very important for the watchmaker is hand height. For SNGLRTY we need the movements to have a hand height of #5. This may not mean very much to most people, but this is at the higher end of the spectrum. The hand height must be tall, so the attachment points protrude through the movement and the module and allow clearance for the hour hand over the dial.
Power To The Complication Plate
The rotational power for the complication plate is taken from the center of the tractor movement. The second hand is on the center axis, and the minute rotational power is taken from the “Mobile Chaussee.” This is the minute wheel with the cannon pinion. It also drives the hour wheel via another external wheel with a pinion drive.
The drive from the Mobile-Chaussee engages with the Reverse-Minute Gearbox, which is on the complication plate. This gear train achieves several goals. First, it transfers the power across the complication plate to the minute wheel. Second, it drives the minute disc counterclockwise and finally reduces its speed of rotation.
Where The Tractor Movement And Complication Plate Mesh
The center axle with all its hand fittings and drives is almost in its original state. We change only one thing on the tractor movement for our purposes, and this is the hour wheel with the hour hand fitting.
The conventional hour hand fitting with height #5 is replaced with one of our design so that a new minute cannon pinion can be inserted. This new minute cannon with its pinion drives the reverse minute gearbox. It meshes with a standard hour fitting #0 placed above it as a crown. So effectively, we inserted an intermediate gear.
True to its name, the reverse minute gearbox fulfills the function of making the minutes run backward and slower. However, it is equally important that the rotation power is transferred from the center of the movement to the outer area of the movement, where the minute disc engages with the reverse minute gearbox.
Flexibility Is Key
Even during the briefing phase for module development, we had determined that we wanted the greatest possible flexibility going forward. Specifically, this flexibility is concerning the size of the display and selecting the diameter of the minute display.
Equally important was that the center of the complication plate or dial had to remain as free as possible so that a decoration plate could cover the inner area of the watch face. The rationale here was to prevent the whole center of the watch face from rotating. Thus, the minute disc is a ring with a large opening in the center.
The reverse minute gearbox is the core of the SNGLRTY complication plate but also includes the date transmission mechanism and the module platine. Excluding the bridges, brackets, and pins, the reverse minute gearbox consists of 5 wheels, pinion, and discs. These are the minute reversing wheel, the minute display pinion, the minute display wheel, the pick-up wheel, and the minute disc. The point to note here is that the minute disc on the SNGLRTY watch face is part of the complication plate.
The new minute cannon pinion, which is located on the center axis, moves the minute reversing wheel counterclockwise at a rate of one revolution per hour. The minute wheel is relatively large to move the location of the power drive physically. These wheels and gears are made of hardened Sandvik steel with a Vickers hardness of 600 HV/1. The wheels and gears have almost three times the hardness of a 316L stainless steel watch case and yet are manufactured to remarkable precision in the thousandths range.
The reversing wheel drives the minute display drive. A pinion, located at the 7:30 position, rotates clockwise and at the speed of one revolution per hour. This pinion transmits the rotation to the level above and the minute display wheel. The minute display wheel is pressed directly on top and rotates in the same clockwise direction and at the same speed.
The minute disc rotates above the minute display wheel. This is held in position by the pick-up wheel. The pick-up wheel is a ring with external teeth and a small neck on which the minute disc with the internal diameter is mounted and held.
The minute display wheel drives the pick-up wheel with the minute disc attached on top of it. The display wheel runs forward (clockwise), and therefore the pick-up wheel runs backward (counterclockwise). The gearing ratio ensures that the rotational speed is reduced by 1/12.
Timing is Everything
In other words, the 60-minute display rotates only 330° per hour. However, this is not visible to the observer as the hour hand advances 30° each hour. Therefore, the closing speed of the hour hand and the minute disc means that 360° is traversed on the minute disc every hour when viewed from the hour hand. This results in the “60” minute indicator appearing at precisely the correct axis of the hour hand on every hour.
As is often the case, the path from mechanics through physics and chemistry arrives at a philosophical or metaphysical question.
A minute indication, traveling backward and slower than a regular minute hand, yet still maintaining accurate time, my thoughts consider whether a slower pace can get you to the correct place on time? Or is there a better route than the direct and most obvious route? Does the speed say little or even nothing about the achievement of the goal? What does this say about the path traveled to the goal too? Again, the focus is on the goal and precision; the best route, or direction of travel, can sometimes be counterintuitive.