Bill Stonehill
381
Of Micro rotors
Hi Peter,
Sorry I don't have a photo of it, but Buren, which is to say Hans Kocher, their brilliant design chief, came out with the world's first micro rotor, which they called a "planetary rotor" in 1957.
Suffice it to say that Kocher himself, perhaps one of the most talented movement designers that the Swiss watch industry produced, abandoned the micro rotor by the time Buren made their last movement, the Calibre 82, which was a 42,800 Bph , double barrel, constant force escapement with bi direction self winding. This movement was design to compete in accuracy with tuning fork watches and be accurate to +/- 60 seconds a month. Whew!!! However, the rotor was mounted in the center, just like all current ETA movements.
What Buren and others who have made micro rotors have soon discovered was that they had the following problems that meant they would never become the standard solution to the engineering of the automatic watches-1) Cost of manufacture 2) difficulty of design and manufacture 3) Need of extensive hand work 3) Tendency to stop because of oil problems, or because the wearer did not move his arm sufficiently.
Intrinsically, planetary rotors have a problem because, not being located in the center of the watch, they only receive a portion of the force transmitted by the wearer's motion. Only watchmaking of the highest order can sufficiently overcome these problems, which is why micro rotors tend to be restricted to a few, very high quality watches, such as Piaget and Lange.
Somewhat like the tourbillon, the micro rotor is not a solution for everyone. It is much more difficult and expensive to make than the conventional lay out of automatic watches, and consequently, much more exclusive. In of itself, any watch with a micro rotor system must be judged to be one of the very highest quality.
Buren made their micro rotors almost exclusively for Hamilton, and the very limited number of makers manufacturing automatics with micro rotors, as well as the very limited number made per year--I doubt there are even 5,000 pieces made world wide yearly--gives a good idea of the rareity and cost of this system.
Makers such as Lange and Piaget overcome the problems of this type of movement by extremely careful workmanship, using rotors as heavy as possible, often of 18K gold, and carefully hand polishing every mechanical surface to a mirror finish to minimize friction. Also, modern oils not available in 1957, have eliminated entirely oil blockage problems.
Paul Gerber's double rotors are a type of micro rotor, but as I pointed out, being located at the center of the movement, they can take full advantage of the angular momentum of the watch, which micro rotors can not.
None the less, I personally consider the micro rotor far and away the most desireable type of automatic watch (I wish I had one!) and watch making at its very finest expression.
