From the beginning, ease of servicing and durability were in the foreground for the design of our new calibre A35. For this reason, we decided at a very early stage already to place the complete winding mechanism on lubricant-free four-point micro ball bearings. The result of this is that frictional losses are reduced to a minimum.
Also for the design of our rotor fabrication for various calibres, it was our objective to make the rotor bearing lubricant-free, quiet and shock-proof, but also to keep the tilt angle as small as possible.
However, as the tilt on a normal micro ball bearing is too large due to the geometry of its raceway, these were unsuitable for our purposes.
The so-called 4-point micro ball bearings already in use in the watch industry, which have a divided inner race and where the bearing clearance is adjusted by connecting or pressing on the 2nd taper ring, were also taken into account.
However, the attempts to adjust the radial play or tilt in a defined way turned out to be difficult due to pressing of the taper ring on a divided four-point bearing on the inner race at an outer diameter of <2.7mm.
A bearing with a precisely defined play had to be developed, as our crown wheels only run on a one-sided bearing in the inner race of the bearing and “tilting away” under stress had to be limited to a negligible minimum. We found the solution in a new raceway geometry for our micro ball bearings. Based on this geometry, the necessary 4-point contact was also achieved. The advantage is that the bearing consists of a single-piece inner and outer ring. In production, these can be machined with closest work tolerances, and afterwards the bearings are assembled using ceramic balls with a precisely defined size or dimension. This way, for example, radial plays of 5.10 or 15µm can be adjusted without any problems.
In addition, the resulting very small realisable radial play only permits a so-called tilt in the µ range, which is of major importance for rotor bearings.
Also to be mentioned is that our new bearings are manufactured from non-corroding special steel and are fully hardened, as it is quite common in the watch industry that the pressed-on taper ring on the inner race on multipart four-point bearings is made of toxic copper beryllium bronze.
As the ceramic balls can be manufactured with a superfine surface structure and neither microbonding nor frictional corrosion occurs, a lubricant can be omitted completely. And since no lubricants can age in this way, an unlimited lifetime is the result.