Balls of Ruby

The gears in a modern automatic winding movement operate such that whichever direction the rotor is spinning in, the rotational effort will be translated into winding of the mainspring. While the arrangement of the gears is simple enough, the real problem is twofold, firstly to do so efficiently, so even small wrist movements will wind the watch, and secondly to do it in such a way that is long lasting. Many early full rotor designs were not the efficient winders we take for granted these days. Also, any time you look in an old watchmakers drawers – you’ll see countless older ETA, AS and even the occasional Eterna or similar design, movements, with their pawl wheels missing and their automatic train holes oval.

MST 471

The movement we’re looking at in this post is the MST 436/470 Roamer 44 jewel automatic from the early 1960s, in which Roamer, decided to do something much more interesting…

Roamer’s first full rotor automatic design the MST410/1 was patented (CH272613A) and very efficient, but prone to significant wear. In the following diagram of the 410/1 automatic mechanism, the rotor turns clockwise turning the attached gear 3. This causes gear 7 to rotate in an anti-clockwise direction, and locks to the lower gear 8 due to the ratchet pawl 17. This transfers clockwise motion to gear 9, and subsequently anti-clockwise motion to gear 6, which winds the mainspring. As the same time gear 7 was rotating anti-clockwise, the rotor was also imparting an anti-clockwise rotation to gear 4. In this case, the pawl 15 engages the ratchet 14 and the plain friction clutch slips meaning that gear 4 and the ratchet 14 are turning in opposite directions, this motion of gear 14 was transmitted to gear 5 via gear 6. Thus motion in an anti-clockwise direction is applied to gear 6 no matter which direction the rotor is turned. While very efficient, with minimal lost motion – there is considerable wear possible in the clutches and ratchets/pawls. From a collector’s point of view though – the MST410 is a blast to wear on the wrist as it sounds like nothing else as it winds.

MST 410

Roamer’s second automatic design, the MST420 addressed this wear to a large extent, but was more conventional in design and somewhat less efficient.

The magnum opus, in terms of automatic movement design at Roamer was the third automatic design and first appeared in the MST436 in about 1963. In this Roamer used coupling clutches, in which ball bearings rotate freely in one direction, but in the other, climb a ramp and lock the motion. While most automatics of the day (and today) are essentially manual wind movements with a very thin automatic module place on top – the layouts are conventionally horizontal so to speak. The MST436 on the other hand, was designed purely as an automatic movement, and was designed vertically. That is, due to the vertical depth required for the coupling clutches, the automatic mechanism is placed between the two main plates of the movement. Normally this would require a small balance wheel and compact train (as it did in the Buren micro-rotors), but in the Roamer, the train has also been placed vertically, allowing for a full sized balance, train and barrel – while providing sufficient space for the automatic wind mechanism. Overall, the design is of the same hight as contemporary automatics at 4.85mm.

Coupling Clutch

These bearings are housed between two plates, in this case beryllium and steel, and in the best grade 44 jeweled versions the bearings were made of ruby. The real advantages being the low friction for efficient winding and potentially unlimited service life. The following photo shows the dismantled clutch.

Coupling Clutch

In the factory manual, it was stressed that the coupling clutch was non wearing (and low friction for efficient winding) – and should only be (dry) cleaned externally – and the function checked. If the unit turns in only one direction, smoothly and with reasonable axis shake, then it could simply be returned to the watch. But,

  • what if a watchmaker didn’t read the manual and put them through the watch cleaning machine with the rest of the movement parts?
  • what if they were rough or stiff due to years of neglect and the evaporation or breaking down of the lubricant?

Then, of course, one should return them to the nearest Roamer agent for economical replacement/reconditioning/servicing. In 1963-4 when the MST 436 was released, that was a fine plan. It was also a fine plan in 1966 or so, when the MST 470 replacement was released. Now, almost half a century later, this is no longer a plausible idea. Fortunately I have a technical bulletin that describes the servicing of these clutches, and I will cover this now.

Step 1: Removing the Cap

Dismantle the coupling clutch. Choose a hole larger than the beryllium (the copper colored part) in the staking set, and choose a flat top stake that fits nicely on the upper pinion. Now if you simply press it out, all of your ruby bearings and disks will fall into the base of the staking set – which is bad. A better idea is to place the clutch on some watch paper, so it will keep it together, but still press out the beryllium cap as shown below.

Step 2: Dismantling

Next, carefully turn it over and remove the beryllium cap. I cannot stress how small these ruby ball bearings are. Be careful.

Then the steel driving disk. Note that the flat side of the bearing centre (Roamer called this the coupling cylinder) faces upwards. The other end is dimpled inwards.

Here are all the components dismantled. The bottom driving disk is made of beryllium. Do not dismantle any further than this. The bearings are being held to the coupling cylinder by oil adhesion.

Step 3: Clean

Now you can immersion wash it to your hearts content, but make sure the wire basket is no coarser than 0.4mm (60 mesh) and that there are no gaps.

Step 4: Assemble

Now, assemble and lubricate in this order. Slightly lubricate the bearing side of the beryllium driving disk with Moebius 9010 and fit it into the clutch. Place the coupling cylinder and fit the 5 ruby ball bearings, one in each recess in the case of the clutch. You may need to gently massage or jiggle them into place. Do not lubricate the square section of the pinion.

Next slightly lubricate the upper (not the bearing side) of the steel driving disk and fit it.

Cap fitted and ready for pressing. Make sure you don’t shatter the bearings – they need to be correctly in place, before you press in the cover.

Lubricate the pinion bearings with 9010 in the beryllium cover and clutch body. Do not do this before assembly. Now, test the function and axial play. They should turn easily and freely in the anti-clockwise direction and lock immediately when turned clockwise.

Congratulations. We’ve just done a factory equivalent service on the coupling clutches, and they’re fit for decades more use.

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