1960 Thin-o-matic T-502

There was a time when my least favorite Hamilton models was anything in the Thin-o-matic line.  It wasn't a particularly long time, and it was mainly because I found the microrotor movements to be very challenging to work on.  I ruined quite a few learning the tricks of the trade.  There's a lot tucked into a fairly compact movement, and you have to be very careful during reassembly.

There are at least 57 different Thin-o-matic models, if you include the TM-line.  The list grows to 85 if you included the Dateline models with a calendar complications.  They're actually great models - just a bit more complicated than traditional manual winding movements.

Thin-o-matics actually come in three flavors.  The first is the pink microrotor calibers that were produced by Buren.  Most of the Thin-o-matics fall into this group.  A smaller group of Thin-o-matics featured ETA movements that were similar to the Accumatic line, just a lot thinner.  The third group is the TM line with silver colored microrotors.

One of the earliest Thin-o-matics was the T-502.  It was the third stainless steel Thin-o-matic and followed the 1959 T-500 and T-501.  The T-502 is unique in that it has a grey colored textured dial that looks like linen.

The T-502 was made through 1965 but the last two years is was the T-502B.  Hamilton used the B nomenclature when there was a change in movement that required a different case design, even though the outside of the watch looked the same.  I'm not sure what changed with the T-502B but I suspect perhaps it opens through the crystal while the original has a two-piece case.

My project watch arrived in "as found in a drawer" condition.  It's pretty beat up and it's missing the crown - a classic sign that the watch opens through the crystal.  Could this be the elusive T-502B?

I had to look really hard at the back of the case.  I don't see a pronounced lip, indicating the back snaps on.  However, it doesn't look entirely like a one-piece case either.

I took bracelet off and could make out a little slit between the lugs that I could fit my case knife into.

With a crisp "snap" the case back popped off.  So this is a regular T-502 as far as I can say.  It even has the classic microrotor drag mark inside the case back from the oscillating weight spinning around.

I don't think this movement is installed correctly... it has two case braces but they are on top of a spring ring that surrounds the movement.  I think the braces should go under the ring.

The two braces are removed, as well as the ring.  Then the movement can be lifted out of the case.  You can see the crown is missing because the stem rusted off.

The dial is in decent shape.  It would be impossible to get refinished properly so I will just leave it as is.  I can clean up the hands at least.

Now that the dial and hands are removed, I can start stripping the parts from the movement.

While the parts are in the ultrasonic, I'll turn my attention to the old Speidel bracelet.  The owner asked me to see if I could clean it up, as it has sentimental value to them.  The bracelet is a calendar design with a little scroll that can be moved through a window to show the month desired - in this case, it was August 1971.  The first step is to remove the dirt and DNA that has accumulated over the last 50 years. 

One cleaning session and two rinses later, and the movement is now sparkling clean.  I also replaced the crystal and gasket in the case back.

The movement is almost back together.  The balance is ticking away but I still have to put the balance jewels back in.  This movement had two odd-ball screws from a prior watchmaker.  I replaced those with the correct screws from a donor movement.

The movement is running nicely!  The beat error is just within my personal specs of 3.0ms or less.  It's not an easy adjustment for this movement so I'm glad I can leave it as is.

With the movement sorted out, now I can turn my attention to replacing the stem and installing a new crown.  The stem will need to be trimmed to the correct length to match the placement of the crown on the case stem tube.  It's a little tricky, as if you trim the stem too short, you have to start all over.

Alright, the stem is trimmed, the crown is on, the braces are installed under the spring ring.  Time to close up the case.

The finished watch looks great now - even on the cleaned up Speidel bracelet.  This watch can now spend some time on the wrist and enjoy not be trapped in a drawer somewhere.