The Sellita SW200-1 defines a fixed geometric envelope.
Case design must be built around it.
Nominal dimensions are not sufficient.
Case geometry must account for:
- fit
- alignment
- tolerance
- functional interfaces
Nominal Movement Dimensions
- Diameter: 25.60 mm
- Height: 4.60 mm
- Stem height: 1.80 mm
These define:
- minimum internal case diameter
- crown tube position
- axial stack baseline
They do not define the case.
Functional Envelope
The movement occupies more than its nominal dimensions.
The envelope must include:
- movement body
- dial
- hands
- rotor clearance
Case design must allow for:
- rotation of the rotor
- clearance to internal surfaces
- variation in assembly
Failure to account for envelope leads to:
- internal contact
- functional restriction
Radial Constraints
Movement diameter does not equal case bore.
Clearance is required.
Constraints:
- insertion clearance
- tolerance allowance
- retention method
Too little clearance:
- assembly failure
Too much clearance:
- movement instability
Clearance must be defined, not assumed.
Axial Constraints
The SW200-1 height is only one component.
The full stack includes:
- movement height
- dial thickness
- hand stack height
- crystal position
- caseback interface
These define:
- internal height requirement
- sealing compression
- hand clearance
Errors in axial definition cause:
- interference
- sealing failure
- assembly issues
Stem Axis Constraint
The stem height is fixed at 1.80 mm.
This defines:
- crown tube centreline
- case flank geometry
The axis must be maintained through:
- movement positioning
- case geometry
- tube placement
Deviation results in:
- misalignment
- wear
- failure
Movement Retention Constraints
The movement must be constrained.
Constraints include:
- radial location
- axial support
- rotational stability
Retention must:
- prevent movement shift
- avoid distortion
- maintain alignment
Incorrect retention leads to:
- positional drift
- functional issues
Sealing Constraints
The movement interacts with sealing indirectly.
Constraints arise from:
- axial stack
- caseback compression
- crystal position
Sealing depends on:
- controlled geometry
- tolerance management
The movement must not be compressed as part of sealing.
Tolerance Considerations
Nominal values are insufficient.
Design must account for:
- movement manufacturing tolerance
- case machining tolerance
- assembly variation
Combined variation defines:
- fit
- alignment
- compression
If not considered:
- designs fail in production
What These Constraints Mean
The SW200-1 does not define a case.
It defines constraints that the case must satisfy.
Correct design requires:
- defined clearances
- controlled alignment
- managed tolerance stack
- manufacturable geometry
Relation to Case Design
These constraints are implemented through:
- Watch Movement Dimensions and Case Fit
- Watch Case Tolerances Explained
- Watch Crown and Stem Alignment
- Watch Caseback Design
- Watch Crystal Fit and Gasket Compression
They are not independent.
Relation to SW200-1 Case Core
This reference defines the constraints.
The SW200-1 Case Core: Movement-Fit CAD System implements them in geometry.
Use this page to understand the system.
Use the case core to apply it.