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Understanding “Overbanking” in Watches: How to Address and Prevent

When the balance wheel and the pallet fork are removed from a watch, winding it causes t

Understanding “Overbanking” in Watches: How to Address and Prevent

When the balance wheel and the pallet fork are removed from a watch, winding it causes the gear train to spin uncontrollably, a phenomenon known as “overbanking”. This situation, characterized by the gears operating as drivers with the pivots acting passively, results in extremely high rotation speeds at the escapement wheel, especially when the mainspring is nearly fully wound. This can not only produce a distinctive “squeaking” sound but also lead to rapid wear of the gear pivots over time.

Purpose of Overbanking in Assembly and Repair
Overbanking serves a crucial role in checking the assembly and repair process of watches. It allows for the quick observation of whether the wheel pivots reliably enter their jewels, the gear alignment and meshing, lubrication of the jewel holes, endshake of the gears, clearance of the wheel axles, concentricity of the wheel tips, and the sensitivity of gear transmission. Similarly, for the dial-side gear train, including complications like calendars, overbanking can swiftly verify their operational reliability. It should be performed with minimal mainspring tension and after all lubrication has been applied.

Interpreting Overbanking Results
A common belief is that if the escapement wheel or the seconds wheel rebounds slightly after overbanking ends, it indicates good gear transmission. However, the presence or absence of this rebound varies with the movement’s design, often occurring in movements with off-center drives and larger mainsprings. This rebound is due to inertia from the mainspring continuing to push forward, causing a slight counter-torque.

The essential aspect to note is that with minimal mainspring tension, the gear train should begin rotating, maintaining motion for at least a full turn of the center wheel. Even if overbanking seems normal, it doesn’t guarantee the movement’s operational condition post-assembly as mainspring tension changes all radial clearances, especially near the power source.

Two Overbanking Scenarios
Overbanking can occur with the movement alone or once the movement is cased. The latter is critical as many issues arise only after the movement is cased, often due to misalignment between the movement’s stem hole and the case’s crown tube or pressure on the movement affecting the plates and thus the gear clearance.

Observations from Overbanking
Particular attention should be paid to periodic resistance, variations in rotation speed, and any signs of stuttering or stopping. These can indicate potential problem areas based on gear ratios or rotational periods, highlighting the purpose of overbanking.

Dial and Hand Assembly Checks
Overbanking also allows for the inspection of hand assembly issues, such as clearance between hands, hands and dial markers, and the seconds hand and the crystal. For example, if a seconds hand consistently stops at a certain position on the dial, it may indicate that the hand is touching the crystal, necessitating adjustment.

The positioning of hands on their pinions and the perpendicularity and radial clearance reflected by the tip height of the hands can amplify issues, especially in older watches where wear is more likely. Overbanking, therefore, serves as a magnifier for potential wear and alignment issues, underlining the adage “the devil is in the details” in watch maintenance and repair.

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