TWEAKING THE MARK XII: PART 2.2
BASIC PRINCIPLES OF WATCH ADJUSTING
by Walt Odets
I have already discussed the concepts of watch timing (“Tweaking the Mark XII: Part 2.1“). In this part of the series, I will discuss the principles used in actually timing a watch. Understanding these principles is predicated on a certain familiarity with the escapement, and a previous Horologium article, “The Anchor Escapement,” is recommended for those unfamiliar. While this exposition is not intended as a pragmatic manual for timing procedures, it will allow the watch owner to understand the issues involved, and to appreciate the complexity of a well-adjusted watch. Inside the watch that “keeps excellent time” one finds both beautifully adjusted watches, and those whose good time-keeping can be attributed to little more than a fortuitous combination of technical short comings and the owner’s personal habits.
THE CONDITION OF THE WATCH
In daily running, the regulation of a watch is, of course, accomplished by the balance wheel and balance spring. But there is an old and correct watchmaker’s adage that, “Good Timing Starts at the Mainspring.” The timing of a watch can be no better than the mainspring, center wheel, third wheel, fourth wheel, escape wheel, pallets and pallet lever, and all their associated pivots, pinions, teeth, and leaves. If the mainspring–through age, mishandling, or incorrect lubrication–delivers power unevenly, that will be reflected in the timing. The power delivery all the way from the mainspring to the balance impulse jewel must be adequate, smooth, and relatively flawless for a mechanical watch to provide consistent, excellent function.
HEIGHT=”136″ ALIGN=”RIGHT” BORDER=”2″ NATURALSIZEFLAG=”3″ ALT=”Timing tape, amplitude”>The best single measure of the condition of a watch is the amplitude of the balance. Amplitude is expressed as the number of degrees of swing of the balance from rest (in the centered position) to the end of its excursion in either direction. In a healthy, freshly-serviced watch, amplitude should be between 275 to 310 degrees in the horizontal (dial up or dial down) position. In a vertical position (crown down, left, up, or right), amplitude will drop about 45 degrees due to increased friction in the balance pivots. Thus, an acceptable minimum for vertical positions is about 230 degrees. Because correct amplitude–good motion in the parlance of watchmaking–depends on every component of the movement, most faults will be reflected in inadequate (or, occasionally, excessive) amplitude. Without good motion, a watch cannot be properly adjusted. No amount of fiddling with the escapement can correct for poor motion.
PARTS OF THE ESCAPEMENT INVOLVED IN ADJUSTMENT
For purposes of this discussion, it is assumed that the entire train of the watch is in good condition, and that both horizontal and vertical amplitude are within correct range. It is assumed that pallet jewels and escape wheel provide consistent and correct geometry. And, finally, it is assumed that the balance wheel, itself, is properly poised. An unintentionally out of poise balance will, obviously, create unwanted effects in the vertical positions of the WIDTH=”280″ HEIGHT=”285″ ALIGN=”LEFT” BORDER=”2″ NATURALSIZEFLAG=”3″ ALT=”Balance cock schematic”>watch. (I have discussed balance wheels and their poising in a previous Horologium article, “The Balance Wheel of a Watch.”)
Those basic and necessary requirements met, the adjustment of the watch is accomplished with adjustments to five critical regulating components. As shown in the schematic of a balance cock (in blue, at left) seen from below, these include the balance spring (1); the stud carrier (2), to which the outer end of the spring, with its stud, is anchored (at 2A); the regulator (3), with its adjustment mechanism (3A); and the collet (4), which rides on the balance wheel shaft, and to which the inner end of the balance spring is attached.
The same components, identically numbered, are also shown in profile, below right. In this view, it can be seen that the balance spring (1) surrounds the collet (4) to which it is attached. The spring spirals outwards, eventually passing between the regulator index (3B) and regulator boot (3C). The spring ends at the stud (2A), to which the spring is attached with a pin or adhesive. The stud is, in turn, fastened into the stud carrier (2) by means of a se WIDTH=”350″ HEIGHT=”194″ ALIGN=”RIGHT” BORDER=”2″ NATURALSIZEFLAG=”3″ ALT=”Schematic profile”>t screw (2B). The regulator housing on top of the balance cock (3D) carries the upper balance jewel set (hole and cap jewels) and shock absorber. In the case of the Triovis regulator on the caliber 887, the fine regulator mechanism is also part of the regulator housing. The balance wheel (5) and balance shaft (5A) are also shown in the profile view.
The ring of the regulator and Triovis ring ride below the regulator housing. All are shown below left. The regulator ring (3) lies on top of the balance cock with the regulator housing (3D) and Triovis ring (3F) on top of the regulator ring, in that order. In other words, the Triovis ring is between the regulator ring and regulator HEIGHT=”242″ ALIGN=”LEFT” BORDER=”2″ NATURALSIZEFLAG=”3″ ALT=”Regulator parts”>housing. The tab of the Triovis ring (3G) is moved by the regulator screw (3A) and the Triovis ring moves the regulator ring. It is by this means that the effective length of the balance spring is adjusted. In watches with regulators, adjusting the effective length of the balance spring is how regulation (adjustment for daily rate) is accomplished. (Watches without regulators must be regulated by means of changes to the balance wheel itself.)
THE HORIZONTAL POSITIONS
The two horizontal positions should measure very close to each other, and this is the first measurement taken in evaluating the adjustment of a watch. In good quality or better watches, rate and amplitude should be within a few seconds per day and about 10 degrees, respectively. If these two positions are significantly different, this must be corrected before any further adjustment.
When differences are found, they can usually be traced to problems with balance pivots or their lubrication, or to the adjustment of the regulator index (discussed below). Other parts of the gear train and escapement may also, occasionally, be at fault. Differences in tolerances or end shake on the pallet lever and other components can shift alignment with changes in position. Large differences in amplitude often suggest that the balance spring may be rubbing on the underside of the bridge (dial up) or on the balance itself (dial down).
THE COLLET AND “POINT OF ATTACHMENT”
ALIGN=”RIGHT” BORDER=”2″ ALT=”Collet point of attachment” WIDTH=”79″ HEIGHT=”88″ NATURALSIZEFLAG=”3″>The collet, as previously mentioned, attaches the inner end of the hairspring to the balance shaft. Unlike the attachment of the outer end of the spring (at the stud holder), the inner attachment (and collet) rotates with the balance. The collet is simply a cylinder that fits on the balance shaft, with a channel to hold the end of the spring. At right the collet is indicated in pink, the cross-section of the balance staff in yellow. It can be see that the spring attaches to the collet at the red arrow. (The green arrow indicates the slot that allows the collet to be spread and placed over the balance staff.) The four-sided (rather than round) collet of the IWC caliber 887 is shown below left, the spring attached to the collet at the red ALIGN=”LEFT” BORDER=”2″ ALT=”Caliber 887 collet” WIDTH=”136″ HEIGHT=”118″ NATURALSIZEFLAG=”3″>arrow. The balance shaft and upper balance pivot are also visible, in the center of the collet. This collet shape simply makes the collet easier to work with.
In the late nineteenth century Jules Grossman, a watchmaker from LeLocle, discovered perhaps the most critical principle of modern watch adjusting: the point of attachment. The point at which the balance spring attaches to the collet (relative to the case of the watch, and thus to the position of the crown) affects the rate differently in each of the four vertical positions. Although traditionally used to adjust watches with overcoil balance springs, the principle of point-of-attachment is also applicable to flat balance springs and is now used in all finely adjusted watches.
ALIGN=”LEFT” BORDER=”2″ ALT=”Pivot, horizontal positions” WIDTH=”210″ HEIGHT=”210″ NATURALSIZEFLAG=”3″>For purposes of adjusting a wristwatch (as opposed to pocket watch), the vertical positions in order of importance (starting with the most important) are crown down, crown left, and crown up. Crown right is not normally adjusted in a wristwatch, but for an owner who wears the watch on the inside of the right wrist, crown right is substituted for crown left. The ordering of these positions is determined simply from their frequency in average wear, and is universally accepted among watchmakers and manufacturers.
One of the most difficult problems in adjusting a watch is the faster rate of vertical positions (compared to the horizontal positions). In vertical positions, the friction of the balance pivots is much higher, which reduces amplitude. The reduced amplitude produces a faster rate (because shorter swings complete more quickly). To the extent that the innate characteristics of the balance spring provide good isochronism (causing shorter swings to complete more slowly, longer swings more quickly), the effect of vertical positions is reduced. But it is never eliminated entirely through good isochronism alone.
ALIGN=”RIGHT” BORDER=”2″ ALT=”Pivot, vertical positions” WIDTH=”280″ HEIGHT=”256″ NATURALSIZEFLAG=”3″>Each attachment point of the balance spring to the collet (at 12, 3, 6, or 9 o’clock) provides predictable corrections of rate: little error in two positions, slow rate in the third, and fast rate in the fourth. Thus, in wristwatches, the point of attachment is usually chosen to lower the rate in the crown down position, the most common vertical position for a wristwatch. Theoretically this is the position illustrated below right. This provides minimal error in the crown right and left positions, fast rate in the crown up, and slow rate in the crown down. While this is clearly a compromise, other points of attachment often provide less satisfactory adjustments.
In a watch adjusted to five (versus three) positions, this theoretically correct attachment may make the crown up position difficult to keep within acceptable parameters. Friction effects on the sides of the balance pivots (particularly with a flat balance spring, with which shifts in the spring’s center of gravity are larger than with overcoil springs) also affect adjustment. Thus, the best pragmatic compromise on point of attachment varies from caliber ALIGN=”RIGHT” BORDER=”2″ ALT=”Geomoetry of POA” WIDTH=”205″ HEIGHT=”178″ NATURALSIZEFLAG=”3″> to caliber. One generally finds Jaeger Le Coultre movements (and IWC’s, like the 887, derived from them) adjusted as illustrated below left. This point of attachment tends to provide moderate error of similar magnitude in all four vertical positions: crown down is slightly slow, crown left slightly fast, crown up slightly fast, and crown right slightly slow. In most high quality watches, correct selection of point of attachment alone should bring vertical positions to within eight to 15 seconds per day of the horizontal positions. Additional correction must be provided by the inate characteristics (mostly metallurgical) of a balance spring that improves isochronism and thus reduces rate in vertical positions, despite the reduction in BORDER=”2″ ALT=”JLC POA” WIDTH=”143″ HEIGHT=”143″ NATURALSIZEFLAG=”3″>amplitude. Obviously, any other faults in the watch that reduce amplitude in vertical positions must also be corrected to minimize the increase in rate. Occasionally, a balance wheel may intentionally be thrown out of poise to improve performance in one or two vertical positions. But this approach is likely to worsen performance in other vertical positions, and is usually considered bad technique. Clearly it is an approach most applicable to watches adjusted in three (or possibly four) positions.
CONTINUE TO PART 2 OF THE ARTICLE
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