Vacheron Constantin Service 6405 – Cal. 1001/2 Free Sprung Balance

Such watches cannot be "repaired." They are studied, respectfully dismantled, and reassembled with absolute discipline according to the principles of haute horlogerie.
This particular Vacheron Constantin ref. 6405, equipped with the legendary cal. 1001/2 free-sprung balance, is one of the most refined examples of ultra-thin mechanics from the 1950s and 1960s and one of the most demanding projects that a modern workshop can undertake.

A landmark mechanism: cal. 1001/2

The cal. 1001 is one of the most delicate manual winding mechanisms ever made by Vacheron Constantin. The 1001/2 version is distinguished by its free-sprung balance, without a regulator, adjusted by means of inertia screws on the balance wheel.
This means that accuracy depends solely on geometry, balance, and correct mass distribution, not on rough interventions. It is a superior solution, but also a challenge for the watchmaker.

Initial assessment & disassembly

During the initial examination, the mechanism showed expected signs of age:

• dried lubricants

• micro-damage on friction surfaces

• need to check tolerances in the escape system

The dismantling was carried out thoroughly, with particular attention paid to the extremely delicate bridges and very small rubies. Photographing and documenting each stage is essential in such work—not only for quality reasons, but also for historical accuracy.

Cleaning & inspection of components

All components were cleaned in multiple stages, using procedures adapted to vintage high-precision watch mechanisms.
Particular emphasis was placed on:

• on the wheel axles

• on the surfaces of bridges with perlage

• in escape and anchorage

The free-sprung balance wheel was examined separately: concentricity check, hairspring alignment, and symmetry of development — critical elements that do not tolerate errors.

Assembly & lubrication

The assembly was carried out in strict compliance with the specifications of the mechanism's era.
Lubrication was carried out using minimal and strictly controlled lubricants, as any excess creates resistance in ultra-thin calibers. The result must be functional, not artificially "polished."

Adjustment without regulator

The final adjustment of a free-sprung balance is perhaps the most demanding stage.
There is no regulator for "quick fixes." Precision is achieved exclusively through micro-adjustments to the balance screws and repeated checks on positions. This is pure watchmaking, as taught in the great workshops of Geneva.

Case, dial & historical integrity

The 18K gold case was preserved without invasive polishing, respecting its geometry and hallmarks.
The dial, with its characteristic patina of decades, was gently cleaned and not "improved" aesthetically, because authenticity is superior to superficial perfection.

The result

The Vacheron Constantin 6405 has been restored to full working order, with consistent performance and character worthy of its pedigree.
This is a watch that reminds us that fine watchmaking is not measured in complications, but in proportions, discipline, and silent perfection.

At The Watchmaker workshop, such projects are treated not as simple service jobs, but as maintenance of the cultural heritage of watchmaking.