In the late 70ies, the swiss Ronda AG launched their caliber line 4x3y, to which belonged the Ronda 4135 shown here. It's a manual wind movement of the smallest diameter (8 3/4 lignes) of this series. All the other movements of this family, upto the 12 ligne selfwindig movement 4439R base on that movement and mostly differ by the size of the main plate and by additional features.
The Ronda 4135 is an econimically built, true pallet lever movement.
It's a contemporarily modern construction with directly driven center second and an indirectly driven cannon pinion on the dial side. The beating frequency is 21600 A/h and its nickel ring balance is beared in two KIF Protechoc bearings.
You can see the efficient construction of this movement on the way, the bearing and cap jewels, 17 of them, are installed: In the plates, there are quadrangular(!) recesses, which the jewels are pressed into. In which way this method is superior than using traditional round holes for pressing in the jewels, is unknown to me.
Unlike most other Ronda movements, which a watch maker sees on his deck, this one is a "RAX" marked movement, which means, that it uses a swiss pallet lever. Nevertheless, some attributes of a Roskopf movement can still be found here, especially the driving of the cannon pinion by the mainspring barrel.
On the dial side, you can also see the economical construction: The mainspring barrel is completely open to that side, and the setting lever angle is just a rather large punched sheet. At "12:00", there's the bearing of the intermediate wheel for the date quickset mechanism, and at "11:30" the long bearing, in which the quickset wheel either advances the date ring, or disconnects it when turned the other way round.
The date mechanism is very interesting: By turning back the time, the correction wheel engages at "11:30" with the date ring and pushes it forward. By advancing the time it slips through, and discouples the mechanism.
To avoid damaging the quickset mechanism, the clutch is moveable and doges when it is turned backward.
The date indication mechanism is clearly the highlight of this movement since it is really unusual and rare, but it is very efficient and due to the U-spring, it's a challenge for a watchmaker.
In the lab
The specimen shown here is a NOS movement, which was probably stored for twenty years, before it got into the lab. It was not serviced at all.
On the timegrapher
On the timegrapher, this unadjusted movement performed well, especially, when you take into account, that it was stored for many years before.
The difference between the vertical and horizontal positions could be the effect of a light gumming of the movement.
Nevertheless, for a rather low end pallet lever movement, the results are absolutely OK, and maybe, if the movement ran for some weeks or a full service were made, it had performed even better.
Thank you very much to the Ermano Uhrwerke Gmbh for the donation of this movement and further technical papers.