Explanation Of How To Regulate A Watch

Walt, can you explain…

Posted by Jaeger on February 05, 1998 at 13:45:59:

How to properly regulate a watch? Why are some at 5 positions, while others at 3? What are the positions? If you adjust for 5 positions, and then for temperature, doesn’t it throw the first adjustment off? What’s isochronism? Are the adjustments all at the same point (i.e., a screw) or does each position have a separate adjustment?

Don’t leave me in the dark, man! I need knowledge!

Posted by Walt A. on February 06, 1998 at 1:49:51:

In Reply to: Walt, can you explain…posted by Jaeger on February 05, 1998 at 13:45:59:

There is a difference between regulation and adjustment. Regulation refers to the process of touching up the variable parameters on an escapement -either the moment of inertia of the balance wheel, (used by Rolex, PP, etc.) or varying the effective length of the hairspring via the adjustment lever, (used by most other watches)- so as to minimize the average rate error of the watch. This work is done by a watchmaker as part of an overhaul or almost any repair involving movement parts. It is also often required at times between overhauls, to compensate the changing viscosity of the aging lubricants in the pivots. For this work to be done properly, the balance wheel needs to be properly SET UP, i.e., positioned so that the hairspring’s ‘neutral point’ is located at the midpoint of the balance wheel’s swing. Most inexperienced watchmakers omit this task and generally get by with the omission. Hi-tech operations, such as Jack Freedman’s Superior Watch Service, use sophisticated equipment to make this operation perfect and totally repeatable. Incidentally, the problem above is mostly limited to watches whose rates are regulated by fixing the length of the hairspring. Watches that change the moment of inertia of the balance wheel usuall stay set up. This includes Rolexes with chronometer movement, Patek Philippe models with the Gyromax balance wheel, etc.

Adjustment is something generally done only by the manufacturer at the time the watch is fabricated. It refers to the meticulous balancing of the balance-wheel/hairspring system so that its center of mass is always located along the axis of the balance staff. If this is done properly, the balance wheel will be immune from perturbations or jolts in the plane of the dial and the beat frequency will be relatively constant in a number of positions. There are six positions, corresponding to the 6 faces of a transparent cube inside which the watch can be imagined to be located. It is difficult or impossible to achieve PERFECT adjustment in all six positions and all adjustments are a compromise of some sort. To save money and improve adjustment in the positions that count, i.e., those the watch is likely to find itself most often, some positions are omitted from adjustment. For a wristwatch, the most commonly omitted position is the 12-UP position, usually assumed by the owner holding the watch upright in front of his nose, but rarely assumed any other time. (The exception is truck drivers and other people who wear their watches on the inside of the wrist). For a pocket watch, the omitted position is the bow-down position (12-Down on an open-faced watch and 3-Down on a hunter case watch). The result in all these cases is a watch with adjustment for 5 positions, an excellent product. Adjustments for fewer positions are found in some watches. In such cases, adjustments are omitted for the least frequently assumed positions in actual use.

Another important adjustment is that for TEMPERATURE. In the days before invar, glucydur, and other alloys having an extremely small coefficient of thermal expansion, balance wheel rims were bimetallic (like the sensing element in your household thermostat) and cut at two opposing points. The free ends at the cuts would move inward or outward with temperature (very slightly, to be sure) and in this way keep the moment of inertia of the balance wheel invariant with temperature. Fine watches were adjusted for constant rate at three temperatures: hot, cold, and on-the-wrist (about 90 degrees F). COSC tests chronometer candidates at three temperatures.

Finally, there is isochronism. The aim of this adjustment is to make the watch’s rate immune to amplitude of the balance wheel’s swing. Obviously, when the mainspring is fully wound, the balance wheel swings very wide, on the order of 270 degrees end-to-end. As the tension of the mainspring ebbs, the amplitude decreases, until it is on the order of 105 degrees end-to-end near the end of its useful power reserve. Isochronism adjustment involves a variety of specialized techniques, the most effective being the Breguet overcoil on the hairspring, which makes the system act to the best degree like a simple linear oscillator, whose frequency in theory is independent of its amplitude. It should be noted that automatic watches are far less dependent on adjustment for isochronism than are manually wound watches, since automatics are assumed to be always at or near their mainsprings’ full usable power. Manually wound watches, on the other hand, can be regulated to compensate for the totally predictable isochronism curve, assuming the watch is wound at the same time every day.

Well, those are the big adjustments. I believe Walt Odets can clarify many things that are missing here, particularly the techniques used to obtain outstanding isochronism. How about it, Walt?