Definition
Within HorologyCAD, movement height and case thickness are distinct but directly related parameters.
Movement height defines the minimum internal vertical space required.
Case thickness defines the total external height of the watch case.
The difference between them is determined by:
- Internal component stack
- Required clearances
- Case structure
- Sealing systems
Case thickness is derived, not chosen.
Why This Relationship Matters
Incorrect handling of vertical dimensions results in:
- Internal interference
- Rotor contact with caseback
- Hands contacting the crystal
- Incorrect gasket compression
- Excessive or unrealistic case thickness
Case thickness must be derived from internal requirements, not defined externally.
Movement Height
Movement height is the total vertical dimension of the movement.
It defines:
- Minimum internal case height
- Base reference for vertical stacking
- Constraints for caseback and crystal positioning
Movement height must be treated as:
- A fixed minimum value
- Not a flexible design parameter
Case Thickness
Case thickness is the external vertical dimension of the case.
It is influenced by:
- Movement height
- Dial thickness
- Hand stack height
- Crystal thickness and clearance
- Caseback structure
- Gasket compression
Case thickness is always greater than movement height.
Vertical Stack Components
The internal vertical stack includes:
- Movement height
- Dial thickness
- Hand stack height
- Clearance above hands
- Clearance below movement (if required)
- Rotor height (automatic movements)
All components must be included in the total calculation.
Axial Clearance Integration
All vertical spacing must include controlled clearance between components.
This ensures:
- No internal contact
- Reliable operation under variation
- Functional assembly
This behaviour is defined in axial clearance (vertical spacing).
Hand Stack Influence
The hand stack defines the upper boundary of internal geometry.
It determines:
- Minimum dial-to-crystal distance
- Required vertical clearance above the movement
This is defined in [LINK]hand stack height and clearance requirements[/LINK].
Rotor Clearance (Automatic Movements)
Automatic movements introduce additional vertical constraints.
The rotor defines:
- Maximum movement envelope
- Required clearance to caseback
Insufficient clearance results in:
- Rotor scraping
- Increased wear
- Reduced winding efficiency
Rotor clearance must include tolerance and dynamic movement.
Crystal and Caseback Contribution
Structural components contribute directly to case thickness.
Crystal:
- Defines upper boundary of internal space
- Requires clearance above the hand stack
Caseback:
- Defines lower boundary
- Includes structural thickness and sealing interface
Both must be integrated into total thickness.
Gasket Compression and Sealing
Sealing systems require controlled compression.
This affects:
- Caseback positioning
- Crystal seating
- Overall case thickness
Incorrect compression results in:
- Water ingress
- Seal failure
Sealing behaviour must be included in vertical design.
Tolerance Considerations
Vertical dimensions are affected by:
- Movement height variation
- Component thickness variation
- Machining tolerance
- Assembly variation
Tolerance stack-up reduces available clearance.
This behaviour is defined in Watch case tolerances (engineering guide).
Failure to account for variation results in:
- Internal interference
- Inconsistent assembly
- Functional unreliability
Relationship Structure
Case thickness can be expressed as:
Case Thickness = Internal Stack Height + Crystal Thickness + Caseback Thickness + Structural Allowances
Each component must include tolerance and clearance.
External Design Implications
Attempting to control case thickness externally leads to:
- Compromised internal geometry
- Reduced clearances
- Mechanical interference
Correct approach:
- Define internal stack first
- Allow external thickness to result from it
Common Design Errors
Typical mistakes include:
- Designing case thickness equal to movement height
- Ignoring hand stack and crystal clearance
- Underestimating rotor clearance
- Ignoring gasket compression
- Not accounting for tolerance stack-up
Each results in predictable failure.
Practical Application
Correct vertical dimensioning enables:
- Accurate internal spacing
- Functional component interaction
- Reliable sealing
- Predictable manufacturing
This is a critical relationship in watch case design.
Interaction with Internal Geometry
Case thickness is derived from internal geometry.
Internal structure defines:
- Vertical stack arrangement
- Interface positioning
- Clearance requirements
This relationship is defined in internal case geometry.
System Context
This page connects directly to:
- Axial clearance (vertical spacing)
- Hand stack height and clearance requirements
- Watch case tolerances (engineering guide)
Each defines a key aspect of vertical design.
Final Statement
Movement height defines the minimum internal space.
Case thickness is the result of resolving all vertical components, clearances, and structural constraints around it.
A case cannot be thinner than its internal requirements.