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Crafting and Repairing the Balance Staff in Mechanical Watches

The balance staff, though minute, plays a pivotal role in the functionality of a mechanical watch, deman

Crafting and Repairing the Balance Staff in Mechanical Watches

The balance staff, though minute, plays a pivotal role in the functionality of a mechanical watch, demanding precise dimensions for each of its segments. Let’s delve into the intricate structure and the meticulous process of crafting a balance staff, using the SZ1 movement as our reference point.

Structure of the Balance Staff
The balance staff, essential for the movement’s accuracy, comprises several critical sections:
– **A** represents the total length from the upper to the lower pivot point.
– **B** details the lower half of the staff, including B1 for the double roller assembly, B2 for the lower shock-absorbing section, and B3 for the lower pivot.
– **C** outlines the upper half, including C1 for the hairspring collet fitting, C2 for the upper shock-absorbing section, and C3 for the upper pivot.
– **D** and **E** define the balance wheel riveting section and the balance wheel seat, respectively, with diameters precisely matched to the balance wheel components.

Crafting Steps for the Balance Staff
1. **Turn the Balance Wheel Riveting Section**: Secure a steel rod slightly thicker than the balance wheel seat diameter in the lathe. The exposed part should be longer than the new staff’s total length. Turn to create a flat for the balance wheel seat and the riveting section, ensuring a right angle between the two for a snug fit.

2. **Turn the Hairspring Collet Fitting and Groove for the Balance Wheel**: After setting aside space for riveting, cut a notch as a marker for the start of the hairspring collet fitting section. Ensure the fitting allows a slight conical taper for easier installation, testing the fit with a collet gauge or gently with tweezers.

3. **Shape the Hairspring Fitting Length and Shock-Absorbing Section**: Base the length of the hairspring fitting on the old staff’s measurements. The shock-absorbing section’s dimensions can be gauged on the old staff using a gauge pin, ensuring a dynamic fit with the shock-absorbing seat.

4. **Turn the Pivot Sections**: Use a rounded turning tool for the pivots, starting with a conical shape before transitioning to a cylindrical form. Ensure smoothness and straightness to avoid bending or breaking. Finishing involves fine filing, polishing with abrasive paper, and ensuring a spherical shape at the pivot tips.

5. **Final Adjustments and Testing**: After basic shaping of the lower half, cut off the excess and repeat the procedure for the upper half, ensuring accurate alignment to avoid off-center pivots which can add imbalance. Final fitting includes adjusting the length and ensuring the balance wheel fits perfectly without excessive force.

Importance of Precision and Finishing
Achieving the ideal balance staff involves not just meticulous turning and shaping but also a keen eye for detail and an understanding of how each section interacts within the movement. The finishing touches, including hardening, tempering, and polishing to a mirror finish, are crucial for minimizing friction and maximizing the efficiency of the balance wheel’s oscillations.

Crafting or repairing a balance staff is an exercise in precision engineering, requiring patience, skill, and a deep understanding of the movement’s mechanics. The effort ensures the heart of the watch beats accurately, reflecting the artistry and technical expertise of watchmaking.

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