Hamilton Thin-o-matic Cal 628
It's the 1960's & "Thin Is In..."
The old familiar pocket watches were still around in abundance in the 1950's & through to the 1960's, & the watchmakers needed a hook to set the new & modern wristwatch apart from Granddad's old pocket watch.
Enter the small & thin wristwatch of the modern era.
The Hamilton Thin-o-matic
It's thin & they want you to know it...
Gold plated case is scuffed & worn, big old scratch in the crystal.
This piece originated around 1965, & has had a good long life by the looks of it.
Let's see if we can freshen it up some & set it off on its next 60 years...
The Thin-o-matic line uses a "One-Piece" case, meaning there is no removable case back, & the watch movement comes out via the front.
To make that work, the watch needs to use
a two-piece stem that clamps itself together in the middle.
Popular design choice in the 60's, but it's not a great system, & most new watch designs today will use a conventional removable case back & single-piece stem.
The crystal is friction fit. There is more than one way to unseat it from the case, but I like to use a little blast of compressed air in through the stem tube to get the crystal to pop out.
The trick is to modulate the airflow such that you provide enough pressure to pop out the crystal, but not so much that you bounce the crystal & watch movement off of the ceiling...
There we go
With the scuffed up crystal out of the way, can see that the dial looks to be in good shape.
Movement is free of the case, now we can get down to the real business of servicing the movement.
Removing the hands.
As with many watch components, the hands are delicate & easily damaged.
In normal use, nothing touches the hands other than the pinion they are attached to, so by design they are as thin & light as possible (important to limit the starting & stopping inertia with each tick of the movement, wherever possible).
Have they mentioned how thin this thing is?...
Turns out, the Hamilton calibre 628 is impressively thin, even by modern comparison; 3.25mm and an auto-wind movement.
But,...
They then choose to implement an hour, minute, seconds hand stack and dial furniture (hour indices) that are nearly as thick as the movement itself. So kind of defeats the purpose.
Modern ultra-thin watchmakers like Piaget or Bvlgari would make every possible effort to flatten out the hand stack & the dial to get the whole watch as thin as possible.
Ah well, still an impressive movement, which we'll soon get to see more of.
Dial side of the movement
Removing the dial & exposing the motion works
(the gearing & pinions that drive the hands)
Wrapping up the dial in watchmaker's dial paper. Lint-free & acid-free paper for protecting delicate parts from incidental damage.
Dial side of the movement.
Interesting to see the heat blued screws securing
the motion works cap.
Not sure what (if anything) made these screws
deserving of special treatment.
Dial washer & hour wheel
Removing the cannon pinion
And that's as much breakdown as we want for now on the dial side
Watchmaker side of the movement
So what, exactly, makes this movement so thin?...
The Hamilton cal 628 is what's known as a "micro-rotor" movement, meaning that the automatic winding mechanism is integrated into the movement itself, as opposed to having a standalone winding module added on top of a separate standalone movement.
This has the effect of sinking the
auto-wind mechanism down into the plane of the rest of the watch movement mechanism.
It's enough of a challenge to get any movement design implemented & working, & for a micro-rotor movement like the cal 628 the watchmakers now need to give up half of the mainplate real estate, & then also rearrange the timekeeping mechanism & everything else around the integrated auto-wind mechanism.
Upper balance jewel assembly
Hole jewel & cap jewel
The hairspring for the balance is extremely fragile
Good to get this out of the way early on & protected from the watchmaker's clumsiness...
More heat blued screws for the pallet bridge, wonder why...
Pallet bridge & pallet
The going train (sequence of timekeeping gears) is partially covered by parts of the winding mechanism. Will need to clear these out in order to free up access to the timekeeping wheels.
The micro-rotor auto-wind adds a good deal of complexity to the movement.
For the best winding efficiency we would want the rotor to wind the mainspring by moving in either direction, & would want the watch to still wind manually via the stem & crown, & would want to ensure that neither system interferes with the other.
So there's a lot going on in a small space...
Ratchet wheel
These two hook-shaped springs have been waiting their whole lives to get airborne on some inattentive watchmaker.
Hopefully today is not the day.
Click & click spring, sliding crown wheel & spring
The sliding crown wheel gets pushed into position to drive the ratchet wheel when the user is winding manually via the crown.
When the user releases the crown then the spring pushes the sliding crown wheel back & disengages from the ratchet wheel. This way the manual winding mechanism does not block the auto-wind which is also acting on the same ratchet wheel from the other side.
Notice the striping on the head of the sliding crown wheel screw.
While winding manually via the crown, this wheel necessarily turns counter-clockwise. In order to prevent the normal action of the crown wheel from unscrewing its own screw, the screw will often use a left hand thread. This way the wheel turning will serve to tighten the screw instead of loosening it.
The striping on the screw head is there to alert the watchmaker to take care in removing the screw, it would be very easy to twist the screw the wrong way in attempting to remove it & snap off the head in doing so (as most beginning watchmakers will learn the hard way...).
Sliding crown wheel & crown wheel screw
If you look closely, you can see the left-hand (backwards) threading for the sliding crown wheel screw.
A more typical movement would just have the one crown wheel & that would be the end of it.
The cal 628 has the added complexity of the intermediate crown wheel & sliding crown wheel in order to let the user wind the watch manually (as most watch owners would want & expect), & at the same time provide a means for the manual wind mechanism to disengage when not actively in use.
Intermediate crown wheel, crown wheel, & crown wheel core
With the overhanging hardware from the ratchet wheel & manual wind mechanism out of the way, we can now turn focus to the going train.
The going train is the sequence of gears beginning with the grand wheel integrated into the circumference of the mainspring barrel, on to the second wheel, third wheel, fourth wheel, & escape wheel.
The gear ratios of all the wheels of the going train, working in concert with the oscillating frequency of the balance wheel & escapement is what provides the timekeeping function for the movement.
Going train bridge
Unobstructed view of the going train
Second wheel
Fourth wheel
Third wheel
Escape wheel
Center seconds pinion
The going train & the escapement are the parts of the watch that 'keep time'. But at its core, the watch movement itself doesn't really have any awareness of time keeping or even the concept of time itself.
The function of the watch movement is to regulate the discharge of power from the mainspring. Over the centuries watch & clock makers have gotten ever more clever in regards to the accuracy & precision of power discharge, but really the only part of the watch that has any relation to the time of day are the hands & dial markers over on the other side of the movement.
Now for the auto-wind mechanism
Winding rotor
Reversing pinion cap
(screws stuck in place)
Have noticed throughout the movement that many of the screws have been overtightened, likely by the last watchmaker to service the watch many years back.
So far, have not been able to get the screws for the reversing pinion cap to budge.
It's not good watchmaking practice to overtighten. The screw heads, shafts, & threads are very small & easily broken. Overtightening places more stress on the parts being fastened than they are designed to support, & those parts themselves are small & easily breakable. And it makes the watch difficult to service the next time, & increases the likelihood of damage to the movement in taking the watch apart like we are trying to do here.
Have not broken the movement yet, but can't say the same for the screwdriver blade...
The honing guide maintains a consistent angle when sharpening the screwdriver blade, & maintains that same angle when flipping over to the opposite side of the blade.
Clean up duty
Comparing the before & after, can see here how the new profile uses a less acute angle for the blade. This will result in a thicker wedge & more blade material making it down into the screw head slot for the problem screw.
Finally...
Reversing pinion & auto-wind click
The reversing pinion does not turn on an arbor (axle), but rather slides freely back & forth between the left & right intermediate auto-wind wheels.
Can see how if the winding rotor (removed earlier) were rotating counter-clockwise, then the reversing pinion would get pushed over to the left, itself then being driven clockwise & then turning the left intermediate auto-wind wheel counter-clockwise.
Likewise, when winding rotor is rotating clockwise then the reversing pinion is now pushed over to the right & is driven driven counter-clockwise (opposite from before). This drives the right intermediate auto-wind wheel clockwise, & the right intermediate wheel in turn drives the left intermediate wheel counter-clockwise (same as before!).
So no matter which way the winding rotor is rotating, the left intermediate auto-wind wheel is always being driven counter-clockwise.
Clever!
The left intermediate auto-wind wheel has more work to do, but for now the view is obscured by the auto-wind bridge.
Auto-wind bridge
Back-half of the auto-wind mechanism
Can see how when the left intermediate auto-wind wheel turns counter-clockwise, this then turns the auto-wind reduction gear clockwise.
The gear ratio between the left intermediate wheel & the auto-wind reduction wheel steps down the rate of rotation, & increases torque.
And the same thing happens again between the auto-wind reduction wheel & the brass auto-wind drive wheel, with the auto-wind drive wheel being driven counter-clockwise at the slowest rate & highest torque at the end of the train for the auto-wind mechanism.
The auto-wind drive wheel then turns the ratchet wheel (removed earlier), which winds the mainspring.
Same action on the ratchet wheel as with winding manually via the crown, but with that force now being applied by the auto-wind mechanism instead.
Auto-wind train of wheels
Done with the watchmaker side for now
Watchmakers are used to dealing with hole jewels & cap jewels in the watch movement that are about the size of bread crumb. The gigantic red ruby that the reversing pinion slides around on just looks bizarre in comparison to what's expected for a movement jewel.
Normally watch movement rubies & sapphires are industrially grown, hence not gemstone grade, & I'm sure that's the case here for this mass produced movement.
But that big ruby is still something to see...
Back to the dial side of the movement
Keyless works
The mechanism for manually winding & setting the watch
Minute wheel cap
Minute wheel
Intermediate setting wheel
Setting wheel
Setting lever spring.
This part also serves as the clutch lever cap.
Clutch lever & spring
Clutch, winding pinion, setting lever, & winding stem
Back over to the watchmaker side of the movement.
Keeping the barrel bridge in place up to now has helped keeping parts of the keyless works from falling out on their own, & we've now taken care of that component group.
Barrel bridge
Mainspring barrel
Top side
Bottom side
Barrel cap
Barrel arbor
Mainspring
In a manual wind movement, the tail end of the mainspring would typically anchor to the inner wall of the barrel. When winding via the crown the user will feel resistance when the mainspring is fully wound & the watch will not wind any further.
Because the cal 628 is an automatic winding movement, the winding action never stops (at least while the watch is being worn on the wrist & moved around). In order to prevent overwinding, the mainspring in an auto-wind movement is made to slip against the barrel wall once fully wound (not anchored to the barrel like with the manual wind movement).
The flange on the tail end of the mainspring serves to press the mainspring to the inside of the barrel wall & provide just the right amount of pressure to hold the mainspring fixed to the barrel wall at less than full wind, but then to also allow the mainspring to slip once the watch is at full wind.
Last bit of disassembly
Lower balance cap jewel
Filled up a decent number of cubbies in the parts tray for this one...
In to the ultrasonic for two cycles of cleaning followed by three cycles of rinse.
The cleaning solution is specifically formulated to dissolve watch lubricant, so it's very important to thoroughly rinse off all trace of the cleaning agent before putting the watch back together.
All clean
Maybe this is why the micro-rotor auto-wind is not so common...
Light layer of mainspring grease for the mainspring & barrel
Small drop of lubricant for the lower balance (dial side) cap jewel
The Incabloc shock absorber holds the jewel assembly
Same treatment for the upper balance cap jewel
Setting lever
Clutch, winding pinion, & stem
Application of grease for where the winding pinion teeth mesh with the clutch.
While winding the watch, the clutch & winding pinion are pressed together & meshed.
While adjusting the time the clutch & winding pinion are separated, & the clutch is engaged with the setting pinion.
The layer of grease allows the two parts to mate or separate cleanly & without metal-on-metal sliding.
Clutch lever
Setting lever spring
Minute wheel cap, minute wheel, intermediate setting wheel, & setting wheel
Like seeing those nice clean parts dropping back into place
That's all we want for now on the dial side, over to the watchmaker side
Mainspring barrel & bridge
Auto-wind train of wheels
Auto-wind bridge
Reversing pinion & auto-wind click
Reversing pinion cap
Winding rotor
Everything up to now on the reassembly has related only to setting & auto-wind.
So now on to the actual timekeeping elements of the movement...
Going train of wheels
Center seconds pinion & escape wheel
Third wheel
Fourth wheel
Second wheel in place.
Can see how the grand wheel of the mainspring barrel drives the second wheel.
The second wheel drives the third wheel.
The third wheel drives both the fourth wheel & the center seconds pinion.
The fourth wheel drives the escape wheel.
For most of the time during the operation of the movement the going train will be stationary. It is only in the brief interval when the pallet unlocks the escape wheel that the power of the mainspring is free to drive the going train forward by one tick.
Train bridge
Center seconds bridge
Manual winding works
Crown wheel & crown wheel core
Intermediate crown wheel
Sliding crown wheel & click
Ratchet wheel
In to the home stretch and on to the escapement.
Can see where the pallet will interface to the escape wheel
Pallet & bridge
Can see the very small measure of lubricant applied to the end facet of the pallet stone
The Moment of Truth
Balance complete
And off it goes...
Can see the pallet & escape wheel at work underneath the balance wheel
For every one oscillation of the balance wheel, the pallet unlocks the escape wheel for one tick forward in time.
How is it making out on the Timegrapher?
Very well, as it turns out.
Would be more than happy with that level of precision out of a new watch, let alone a vintage piece like this.
They built 'em well back in the day.
Last bit of work on the dial side
Cannon pinion
Hour wheel & dial washer
Ready for the dial
Using a hands press to set the hands to their pinions
Important to have the hands set straight & level relative to the dial & to each other.
That looks pretty square for the hour hand
Placing the minute hand such that both hour & minute hand align at the top of the hour
Hand stack looks good
Bringing it all together
Finished
Fairly normal sized men's watch for the era, but then with very small lug-width (& super-skinny strap...).
Guess the designers just wanted to try something different.
I kind of like the uniqueness of it.