Watches Advanced

All watches from the railroad era used a balance wheel as a means of achieving accuracy, and when paired with the escapement, let down the mainspring at a controlled rate. The earliest balance wheels were solid metal, while later models had expansion cuts to adapt for temperature changes and carried many pairs of weights around the rim of the wheel that added mass. Its steady beat was controlled by an oscillating hairspring, and most brands had some kind of regulator for fine adjustments that slightly increased or reduced the working length of the hairspring to adjust the rate.

These paired screws were used to make bulk timing changes by turning them in or out slightly. They were usually found near the balance wheel arms and were made with a special interference thread to prevent them from turning without force.  Any company that failed to install them on their watches invited a century of hacks to molest the other weights to make timing changes.

When a watch inevitably slowed from thickening oils and had no mean-time screws to make adjustments, the lazy choice was to simply grind off the balance weights to gain time. At some later point the watch was cleaned properly, which then ran too fast because of the missing weight, so washers had to be added to increase mass - all of which ruined the positional accuracy. 

Any anchor or lever escapement requires a roller jewel, which is mounted in the roller table. On every cycle of the balance wheel this jewel gives an impulse to the pallet fork via the cup at the end of the pallet arm. A guide pin behind the cup prevented the pallet fork from drifting too early by meshing with a crescent-shaped cutout milled in the edge of the roller table.

Overbanking occurs when the roller jewel becomes misaligned with the pallet, which was possible with the single roller design. The double roller was developed to address this, using a smaller lower table with an indent to mesh with a horizontal guard pin. This allowed the pallet arm to swing only when the roller jewel was in the cup, virtually eliminating overbanking.

The stopworks, or Maltese Cross, originated in Switzerland in the 1700s as a means of limiting mainspring travel in watches. A single-tooth drive cam was mounted on the barrel arbor, which mated with a driven wheel that had several open spokes and a single closed one. After a given number of rotations the closed spoke would lock the drive cam and prevent the mainspring from turning.

Most stopworks have been tossed by lazy hacks as unnecessary.

The intent of stopworks was isochronism, the ability of a watch to run at the same rate despite any changes in its power source. The red line in this graph shows the drive torque of a mainspring, and the stopworks allowed the movement to run only in the middle two-thirds of its linear force, where its power was most consistent. While the accuracy may have been slightly improved, stopworks also reduced the run time on a 40-hour spring from roughly 35 hours in real time down to 24 hours.

Open face was by far the most common, with the winding stem at the 12:00 position, and was available in every size that American watch companies had to offer. This configuration eventually became one of the primary railroad criteria.

There are four styles for open-face cases:  threaded covers, snap-on covers, internal swing-ring, and hinged clamshell.

Hunter (hunting) placed the stem at the 3:00 position, and was not railroad approved. The cases have a front lid to protect the dial and glass crystal, which opens by depressing the crown.

There is no such thing as a double hunter or a half hunter.

A case is either hunter or it's not, though demi-hunters have numerals on the front lid and a small crystal to view the hands.

Sidewinders are hunter movements in open-face cases. Seldom purchased this way historically, this arrangement means the original gold-filled hunting case has likely been melted down.

Most collectors believe this configuration to be incorrect.

Conversion dials allowed hunter movements to be used in an open-face case by moving the seconds bit to the 3:00 position, returning the winding stem to 12:00. These began showing up after WWI, were usually made of metal or enamel, and could be railroad acceptable.

Reversible cases had a center ring that rotated within the frame, displaying the movement in either hunting or open-face style. This does not convert the movement, since its winding pinion doesn't change positions. For example, an open-face movement used as a hunter profile will simply be aligned as a sidewinder.

These were also called a Muckle case, after inventor E A Muckle.

The verge dates to the 1200s and used a pair of steel paddles mounted 90 degrees apart on the balance staff to alternately lock and release the crown wheel. It was bulky and the mating surfaces wore quickly, although they could be made very small. Combining the verge with a fusee made small watches possible.

Verge fusees inevitably speed up over time because of the wear of the mating surfaces. The soft brass teeth of the crown wheel become worn out against the steel paddles on the balance staff, reducing the travel of the balance wheel. This decreases the amount of time between impulses, causing the watch to gain.

The fusee was a very simple yet effective method of equalizing drive torque as the mainspring unspooled and lost power. The design dates back to the 1400s, with the earliest versions using gut or wire. When the watch is fully wound, the chain is coiled entirely around the fusee cone, and the mainspring is applying the largest force with the smallest amount of leverage. As the mainspring unwinds, the chain begins to wrap around the mainspring barrel, and its weakening pull is applied to the expanding spiral radius toward the bottom of the fusee cone.