The Story of a Wrist Watch

Co-Written by

Anupama Varadarajan & Adwaith Kumar

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Wind back to childhood – a fascination for precision and aesthetics

The almost imperceptible ‘tick-tock’ sound(except when held close to the ear), the myriad shapes of the dial within, the perfect harmony of the two/three needles rotating on a tiny ‘Dial’, the staid, jazzy or colourful straps – a machine that supports and exasperates us – Adwaith has always been fascinated with watches – especially wrist watches. He marvels at the precise engineering that goes into making these tiny machines. He is especially impressed by branded watches for all the right reasons - functionality, aesthetic design and the finesse of the end product. He still recalls the first watch that he bought as a kid - a Casio watch that caught his attention for both the mechanics as well as the design.

Move forward … to Grade 11….Hitting the Bull’s eye in Maths

Having always been good at Math and Science, it was no surprise that he opted to take up a few advanced topics along with the general syllabus for the calculus portions - when he was in Grade 11. He connected with his grandfather, Shri Ramasamy, to get a better shot at mastering these subjects. Needless to say, grandfather-grandson, the teacher and the taught, hit off beautifully together, conquering one topic after another. Finally, hi-fives and beaming smiles marked a perfect 5/5 score in Calculus. This was a moment of great pride for the loving grandfather – whose maths teaching skills travelled across the Atlantic for the first time (!!!) after having been circulating in Madurai and Bengaluru – producing great results everywhere.

Adwaith, is currently pursuing his BE in Mechanical Engg. at the Univ of Texas. While his grandfather (also my father-in-law), happily divides his time between performing household chores, a regular exercise routine, teaching maths and now learning Sanskrit online !!!

A new Time tracker

A thousand moons or Sahasrachandra Darshanam (Sanskrit), marks one turning into an octogenarian. The whole family had unanimously decided to celebrate my father-in-law’s 80th birthday in the traditional manner. Since it was decided in advance, Kumar (my brother-in-law) was able to plan the visit with his family (his wife Rathi and sons Adwaith and Atharva).

Once they had settled in after their arrival and the delightful and happy banter done with , there was the usual handing over of gifts. But all was not over. There was one more tiny package waiting in the big suitcase !! On his father’s gentle prompt, a slightly shy Adwaith brought out the package, opened it and placed a beautiful wrist watch on his grandfather’s wizened but soft wrist. These days, thanks to the ubiquitous mobile phone, the wrist watch is under an existential threat (at least that’s what it looks like since for most of us, our wrist watches are languishing in our drawers longing to see the daylight).

Delight gave way to curiosity since we realized that there was obviously something special about the watch.

On further prompting, out stumbled the fascinating story of this watch, custom made by Adwaith – a unique and loving creation – with so many challenges along the way before it took its final shape. And the specialty was that he ended up using many of the concepts he had learnt as part of his grade 11 calculus curriculum from his grandfather.

The seed

On a relaxed afternoon, Adwaith was casually browsing the ebay website looking for Rolex watches and of course having sorted on ascending order of price. He came across an original Rolex dial where the watch was no longer functional. The more he looked at it, an idea started taking shape in his mind and became quite firm. From here on, it was an exciting journey marked with challenges, frustrations, resolutions that resulted in a fully functional wrist watch with a sleek and elegant look – turned out to be such an apt and thoughtful gift.
And could be fittingly termed as ‘Gurudakshina’ – a gesture of gratitude on part of the student to his teacher.

His College – the great learning ground

Sure enough, his university is well endowed with state of the art facilities for students to pursue their academic interests and to hone their skills by constant experimentation in their chosen field to try anything and everything. Adwaith made the best possible use of his environment. This little project was taken up by him in his second year.

He used a plethora of tools – both hardware and software. For the software – Design software packages such as Solid Works, Fusion 360 etc. From a hardware perspective, he made use of the following machinery – a 3D Printer and a CNC Machine to physically produce the watch.

It is the story of all the right factors coming together towards a successful goal – the passion, the intent, confidence in the idea, making the right use of the facilities available at and a drive to try concepts hands-on. Its like Messi’s self-belief on Argentina winning the last World Cup ….it was a foregone conclusion from the whole world , like an idea whose time has come !!!!

Read on further … 📖

The Chronology

Step 1: The Watch Dial

The Rolex dial being the core, the complete design had to be centered around the same, literally as well as figuratively !!! So it had to be a watch with a round face.

Step 2: Determine the basics of the design

The next step was to come up with the design – mainly decide its size accounting for key dimensions of the watch case such as diameter, thickness, curvature etc. to name a few. And there could be no compromises on the final look and feel of the watch - the core reason why he had started looking for a Rolex watch to start with.

Step 3: Choose the components and the raw materials

Spec out components that would match this basic design. This is when he chose the movement, the strap, etc. Apart from this, he had to decide the material the watch was to be made of – whether stainless steel or any other material. He chose to make the watch out of Titanium metal. The reason he chose titanium is its low density and toughness. The low-density would ensure the watch has a light feel. Its toughness would make it last long. However, this very attribute added a dimension of challenge when producing the actual watch. And from an aesthetics perspective, he likes its colour. For the strap, he chose a leather one.

The Movement, dial, strap etc. are terms that refers to the various parts of a watch. To make the story easily comprehensible, I am giving a one liner on what is a Movement in a watch.

Movement : It includes all the internal parts of a watch that help it track time. A Watch Movement includes many small parts like springs and gears, but are referred to as a singular ‘movement’.

If interested to probe deeper, you can delve into these websites for a better understanding on the parts of a watch

Step 4: Order the Movement

He ordered a Movement that was of Japanese make - the Japanese Miyota Movement was chosen because it had the correct outer diameter and hand shaft diameters to fit the dial. Still there were some challenges he had to address and fix.

Step 5: Design the Watch

He produced a basic model of the Watch on the computer using the CAD softwares (Solid work, Fusion 360 etc.). As with any design, the model had to go through multiple iterations before he was satisfied with the final output on the screen, at least to start with.

Step 6: Produce a physical prototype

He used the 3D printing machine to get the initial physical prototype with plastic as the raw material. The purpose of printing in plastic is that it is cheap and fast and let him iterate the aesthetics and the way everything was to be assembled.

(Note: Check out on the 3D Printer

)

Step 7: CNC Machine produces the physical Watch

This is the step that actually produced the physical watch using what is known as a CNC Machine. This is available in his college for students to test all their respective ideas. It took the CNC machine nearly 5 hours to produce the watch.

(Note: Check out on the CNC machine

Step 8: A Watch with the perfect look

The watch comes out of the CNC machine perfectly , but wait! he needs to pep it up a little bit. And what does he choose? He chose to polish the Titanium case with a high-end diamond paste. Had to buy a felt tool to rub in the paste onto the Titanium. He used the right amount of diamond paste as per his instincts to get the right shine (he didn’t want it to be either too shiny or dull). The case was taken to a very high level of polish. He could have given a bit more polish but that would not have been good – susceptible to showing up scratches that are thinner than a hair thus ruin some of the effect. The polishing took nearly a month to complete.

All the Math

All of this stuff happened during steps 4, 5 and 6. All of the math informs the design and the design informs the math. The core work was to put together a set of equations considering all the key parameters to design the watch.

The core math problem is sizing the interference fits. This happens between the crystal and the case as well as inside the watch between the movement ring and the housing. We need to manage the tolerances, any thermal effects, shock resistance, durability over time, while maintaining the fit and finish of everything

There are separate equations for all of these factors and the problem we need to solve is to create an equation that combines all of these formulas together and then optimize this combined equation

This combined equation is in the form of a complex differential equation and these were the fundamentals he had learnt from his grandfather as part of Grade 11 syllabus.

The Nuts and Bolts and how it all added up

Critical factors to design a watch

Must look good. All of the parts have to align perfectly without any gaps. The Watch itself should be nice to see.
The design must be manufacturable. One can draw any shape on the computer but it must be possible to produce a real part from that design
Disassembly and maintenance must be simple enough to be done through a facetime call. Ideally not needed at all. The movement is sprint powered and self winding. So it does not need battery changes and unless damaged by dropping or liquids, it should not need any service for at least 15 years !!!!
In general, parts of a wrist watch are very small and any mistakes are very visible. So each part must be perfect.
Account for all types of real life situations a wrist watch can potentially face. It can be dropped from any height, hit against something (from a mattress to a boulder !!!), experience vibrations, subject to magnetism, temperature changes where parts expand at different rates (e.g., the unlikely scenario of putting the watch in the freezer or taking a trek to the North Pole wearing this watch 😊) exposure to dust, liquids like water, tea, coffee etc.The various parts need to fit together : A few instances

The glass has to be bigger than the Watch case

Needed to ensure that the Movement was able to sit perfectly in the center of the watch case without moving about

Rolex dial and the Movement

Alignment of the Date window on the case to the Date display on the Rolex dial

Challenges & Solutions

The Movement was not compatible with the Rolex dial. The original Rolex dial is only compatible with the Rolex movement from the 60s that it came with. This was a challenge. He needed to engineer on how to make these work together – i.e., the Rolex Dial and the Japanese Miyota Movement.

Had to modify the Dial feet (a sub part on the Dial) and the Date disk (a sub part on the Movement) to fit the dial perfectly
The Movement was disassembled, replaced the date wheel/disk with a different one that would perfectly align with the Dial.
On the Dial he had to design a part that would align it radially to the Movement (NB: Please refer to the section Additional Information at the end for more details on this, if interested

⁠Nature of Titanium and limitations of the CNC machine : Titanium is a very difficult material to work with. It has great mechanical properties as a finished product but its toughness makes it difficult to form it into the right required shape as he desired and had managed to produce using the 3D printer.
The CNC machine has limitations in feature size and reach. There are geometries that a 3D printer can easily produce that a CNC will never be able to create. So he had to further customize and make some compromises. The CNC machine cannot produce undercuts and sharp internal radiuses that a 3d printer can.

A precise set of instructions has to be given to the CNC machine to produce any artefact. There is a pre-requisite to get this vetted with the person in-charge of the machine since this is very expensive and used to build various products. Tends to get damaged easily damaged in case of an incorrect instruction. It is important to choose the cutting bit of the precise size and type based on the material that is being fed into the machine.
Hold your breath - It took nearly 5 hours for the CNC machine to produce Watch case. & The shape had to be changed twice due to its limitations.

⁠Fit the glass to the case without using glue: This turned out to be big challenge to resolve. He was very particular on not using glue to fit the glass to the case as this would cause many problems. Using the glue is very difficult. Any air bubbles or gaps or irregularities in how it is dispensed would make the watch look very ugly. This also makes maintenance easier. Not just Rolex but any company that applies glue to glass for any product will have very exacting processes like robots and vacuum chambers for this purpose.

He used what is known as an interference fit formula to fulfil the need to fit the glass and

the case together sans glue. (Please refer to : https://en.wikipedia.org/wiki/Interference_fit )

Including some interesting stuff here for all the engineers 😊

The formula that was used to fit the Watch cover (made of glass) to the Watch case (made of Titanium): Interference fit radial/hoop stress formula

p = pressure
R = nominal radius of hole - this refers to the area where the glass sits into the case. There is an opening in the titanium for the glass to sit.
E = stiffness
r = radius
v = Poisson’s ratio which is effectively a stiffness value
The symbol in the numerator on the RHS the amount of overlap
Symbols with the subscript ‘o’ refer to titanium
Symbols with the subscript ‘i’ refer to glass

   The tolerances of all of the parts stack up (Sum of parts is greater than the whole !!! In this scenario, each minor tolerance adds up to make the problem really big). When one makes a design on the computer, all sizes are exact. However, in real life there is some variation in the size of the parts (though very minor and often invisible to the naked eye). Inside the watch there are many parts that are of varying sizes. This variation keeps adding up and needs to be managed.

   The accuracy is known as the tolerance. When a part is produced in the real world it won’t be accurate to 0.000000. There will always be some deviation depending upon the material and the manufacturing process. This variation exists for every part in the assembly and must be managed to ensure that everything is assembled properly and that there is no rattle or wasted space.

For the titanium case the tolerance of the diameter of the hole where the glass sits is roughly +-0.05mm. Reaching tighter tolerances increases costs exponentially and all of the equations need to be validated for the best and worst case tolerance of every part.

Before we sign-off on this piece, the concluding quip from Adwaith

“None of the engineering choices should interfere with the design. Whenever anybody holds the watch they should only see its beauty. All of the engineering choices should be in the background”

Acknowledgements

To Adwaith Kumar - (😄) for being so forthcoming to share the story. For patiently explaining the details to me , clarifying all my doubts and filling in all the technical details. I have simply used his input ASIS in my narrative for he had articulated the details so well. I was able to fit these neatly into my narrative
To Srishti N Kamath - An artist in her own right since her childhood. She is my friend's daughter and currently pursuing her Bachelors of Design in Communication design. I had reached out to her hoping to see if she could help me generate a few cartoon/pics relevant to this story and sure she helped me. She in fact empowered me with the right AI tools to help me generate the relevant images/pictures on my own. She taught me to use the a combo of Chat GPT and Google Gemini Nano banana to generate the images. And sure enough, I really enjoyed using this new skill.

Additional Information

(NB : Info presented in this section sourced from the internet resources. Included if someone wants a slightly greater deep dive)

Dial feet and Date Disks

Consider a Simple Analogy

Dial feet = Mounting screws that hold a painting frame in place.
Date disk = The rotating calendar page behind a window.

All About Dial feet

Dial feet are tiny metal pins attached to the back of a watch dial. They

Dial feet = Mounting screws that hold a painting frame in place.
Extend from the underside of the dial
Fit into matching holes in the movement
Secure the dial firmly to the movement
They are Important
To ensure hour markers align perfectly with the movement.
Critical for date window alignment
Stability
Prevents dial rotation or shifting inside the case
Clean Construction
No glue needed (in traditional builds)
Professional mechanical attachment
How They Are Secured
Dial feet insert into holes in the Movement mainplate.
Tiny screws on the side of the Movement clamp them.
Feet must match the exact movement model.
Otherwise, dial feet must be cut off and the dial is attached using dial dots (adhesive).
Dial feet position must match the chosen movement.
Changing movement = often redesigning dial feet placement.
Thickness of dial matters for hand clearance.

In many movements (like ETA or Miyota types):

If using a custom dial:

Design Considerations - If you're specifying components:

All About Date Disk

A date disk (or date wheel) is a rotating ring inside the movement that displays the date through a window on the dial.

Has numbers 1–31 printed around it.

Advances once every 24 hours.

Is driven by the calendar mechanism.

Must match movement’s date disk diameter and position.

You can’t arbitrarily place the window unless using a custom date ring.

Font Compatibility

Date disk font should match dial typography - Otherwise it looks mismatched.

Color Matching

Cut off numbers

Show half digits

Look unprofessional

That’s why dial feet positioning is precision engineering.

Customize date disk fonts

Use color-matched disks

Precisely engineer dial feet placement for flawless alignment

Where It Sits : Sits under the dial
Design Considerations (Very Important)
When designing a watch: Date Window Placement

Any mismatch between Dial Feet & Date Disk: If the dial is slightly misaligned (wrong dial feet placement), the date window will

In Luxury Watch Design : High-end brands like Rolex, Patek Philippe etc

Customize date disk fonts
Use color-matched disks
Precisely engineer dial feet placement for flawless alignment