The Sellita SW200-1 is widely used.
Most cases built around it do not fail visibly.
They fail dimensionally.
The failure appears during:
- assembly
- sealing
- long-term use
The cause is not complexity.
It is incorrect geometry.
Failure Starts With Assumptions
Most case designs begin with:
- external shape
- approximate movement dimensions
- visual alignment
This approach ignores:
- tolerance
- stack variation
- interface constraints
The result is geometry that only works nominally.
Movement Fit Is Not Defined
Common issue:
- case bore matches nominal movement diameter
This ignores:
- machining tolerance
- movement variation
Result:
- some movements do not fit
- others move inside the case
Both are failures.
Stem Alignment Is Incorrect
The stem defines a fixed axis.
Many designs:
- position crown visually
- ignore axis definition
Result:
- misalignment
- binding
- wear
This failure is not correctable after machining.
Axial Stack Is Not Controlled
Designs often:
- sum nominal heights
- ignore variation
Result:
- hands contact crystal
- caseback cannot close
- gasket compression is incorrect
The system fails under tolerance extremes.
Sealing Is Not Engineered
Sealing is often treated as:
- adding a gasket
- assuming compression
Without defined geometry:
- compression is inconsistent
- sealing varies between units
This results in:
- leakage
- unreliable performance
Crown Tube Integration Fails
The tube is often:
- added late
- poorly aligned
- incorrectly sized
Result:
- crown does not engage correctly
- sealing fails
- tube loosens over time
Tolerances Are Not Defined
Nominal geometry is not sufficient.
Without tolerance:
- assembly becomes inconsistent
- function varies across units
Designs that work once fail in production.
Machining Constraints Are Ignored
Geometry is often:
- not machinable
- not accessible
- too complex
Result:
- features cannot be produced
- tolerances cannot be held
The design fails before assembly.
Failure Appears Late
These problems are not visible in CAD.
They appear:
- during machining
- during assembly
- during testing
At this stage:
- cost increases
- redesign is required
Why This Happens
Because the design is:
- nominal
- surface-driven
- not constraint-based
It does not account for:
- real movement geometry
- tolerance
- manufacturing
What Prevents Failure
A correct system defines:
- movement fit
- stem axis
- axial stack
- sealing interfaces
- tolerance strategy
Before external design begins.
What the SW200-1 Case Core Does
The SW200-1 Case Core removes these failure points.
It provides:
- defined movement integration
- fixed stem axis
- controlled axial stack
- tolerance-aware geometry
- manufacturable structure
It replaces assumption with constraint.
What This Means in Practice
Instead of:
- testing multiple iterations
- correcting alignment issues
- adjusting geometry after failure
You start with:
- a valid internal system
- correct interfaces
- manufacturable geometry
Relation to the System
These failures originate from ignoring:
- Watch Movement Dimensions and Case Fit
- Watch Case Tolerances Explained
- Watch Crown and Stem Alignment
- Watch Caseback Design
- Watch Crystal Fit and Gasket Compression
The case core implements them.