I assembled a wrist watch.

I try not to touch my cell phone as much as I could, the none stop bombardment of notifications for the latest ‘breaking news’, ‘shocking’ thirty second videos that are designed to elicit the strongest possible emotional response.

Back when everyone worn a wrist watch, 38mm diameter seems to be the standard for man’s. For whatever reason new watches have grown to a size that defies reason. I guess wrist watch have became a fashion accessory that are designed to be noticeable from a distance. After all, you want people to notice your new $3000 purchase, right?

But all I want is a simple tool that keep me in sync with my surrounding that is light and comfortable to wear. So the other day, I assembled my own wrist watch.

The watch is build around a TMI NH38A. Many watch enthusiast will dismiss this Japanese movement for its low beat rate and smaller balance wheel[1]. The lower beat rate translates to less overall wear and tear and the lighter balance wheel places less load on its balance shaft when subjected to shock. It is not unheard of for such movement to run for 10 years without an overhaul. This specific movement also lacks a date mechanism. Date function is aesthetically symmetry breaking and mechanically prone to failure, so that’s a plus for me.

The dial I choose for this build has a matte black finish, this creates a good contrast with silver, brushed metal hands for better visibility. The dial and hands are lumed with BGW9 that glow blue, again for readability in the dark.

The 38mm watch case is light and wearable. The case of a diving watch design, there are two main advantages:

1. Without exception, diving watch have screwed in crown, this prevents water and dust ingress and slow down the oxidation of lubricants in the movement, making the movement longer lasting.

2. The rotating clicky ring is a simple, convenient way to track time for workout and cooking. This ring was used for tracking remaining oxygen before diving computer becomes a thing[2].

After casing, the watch runs at +7 seconds per day, not bad for this $30 movement. I plan to regulate the watch in a month, after the movement become stabilized. Some might disagrees with the existence of the break in period, but in my experience, new movements tend to slow down by a few seconds before the end of the first month.

[1] A higher beat rate and larger balance wheel stores more kinetic/potential energy. In terms of electronic oscillation circuit, this means a higher load capacitance which will reduce the effect of external disturbance. While electronic interference can be shielded somewhat easily, this is not the case for mechanical oscillator where the primary form of interference is acceleration. The heavier balance wheel used in Swiss designs have a real advantage.

[2] A more accurate way to track elapsed time is with a chronograph(watch with a build in stop watch). A chronograph movement is vastly more complicated and expensive than a basic movement. Maintaining such movement is out of my current skill set.

😎 decant

Apr 30 · 3 weeks ago · 👍 skyjake, drh3xx, stack, ResetReboot, Ruby_Witch, norayr, corscada, requiem

3 Comments ↓

🐙 norayr · May 01 at 00:26:

huh, thank you for sharing. i wanted to do something like that and didn't even know where to start. i didn't know there are these modules available, and even after i have read this, i wonder how did you prepare or by the face, the arrows and the case.

are generic different cases also available to purchase? i didn't know anything is available or possible to change except the wrist band.

so apparently the watch is like a pc, it is possible to buy parts and assemble yours?

🚀 stack · May 01 at 00:48:

I was obsessed with mechanical clocks in 2nd grade, and received (and promptly dismantled) many broken clocks... Are you a pro or is it a hobby?

😎 decant [OP] · May 06 at 01:23:

@norayr To start, you should check out /r/seikomods, there are also videos. @stack This is one of my hobby, the other being computers.