The Sellita SW200-1 is one of the most widely used automatic movements in modern watchmaking.
It is frequently treated as interchangeable with ETA 2824-2.
It is not.
Case design must be based on actual movement dimensions and constraints, not assumptions.
Movement Overview
The SW200-1 defines a fixed envelope.
Key Dimensions
- Diameter: 25.60 mm
- Height: 4.60 mm
- Stem height: 1.80 mm
These values define:
- minimum internal case diameter
- crown tube position
- axial stack baseline
The case must adapt to them.
Movement to Case Fit
Radial Clearance
The movement diameter does not equal case bore diameter.
Clearance must account for:
- machining tolerance
- insertion
- thermal variation
Too tight:
- assembly becomes inconsistent
Too loose:
- movement instability
- dial misalignment
Axial Stack
The SW200-1 height does not define case thickness.
The stack includes:
- movement height
- dial thickness
- hand clearance
- crystal position
- caseback interface
If not controlled:
- hands contact crystal
- caseback cannot close
- sealing fails
Stem and Crown Position
The stem height is fixed at 1.80 mm.
This defines:
- crown tube centreline
- case flank geometry
Misalignment cannot be corrected during assembly.
Failure results in:
- stem binding
- premature wear
- keyless works damage
Movement Retention
The SW200-1 requires controlled retention.
Common methods:
- movement clamps
- spacer rings
- integrated shoulders
Retention must:
- prevent rotation
- prevent axial movement
- avoid distortion
Incorrect retention leads to:
- positional instability
- long-term wear
Caseback and Sealing
Caseback design must account for:
- gasket compression range
- thread or press interface
- axial tolerance stack
The SW200-1 does not tolerate uncontrolled compression.
Too much:
- movement distortion
Too little:
- sealing failure
Crystal Interface
Crystal position is defined by the axial stack.
Key constraints:
- clearance to hands
- compression of gasket (if used)
- seat geometry
Failure results in:
- contact with hands
- sealing issues
- structural stress
What Goes Wrong
Most SW200-1 case issues are dimensional.
- Crown tube does not align with stem
- Movement is not properly constrained
- Caseback over-compresses the stack
- Crystal clearance is insufficient
- Tolerance stack prevents assembly
These issues are not visible in CAD unless constraints are defined correctly.
Relation to Case CAD
This movement defines the constraints.
Case CAD defines:
- how those constraints are implemented
- how interfaces are controlled
- how the case can be manufactured
See: Watch Case CAD: From Movement to Manufacturable Geometry
Access
HorologyCAD does not offer custom design services.
The focus is on building movement-led case systems that can be used directly.
SW200-1 case geometry and reference CAD will be released.
Join the list to get access when available.