Definition
The NH35 / NH36 case design guide defines the constraints required to integrate the movement into a functional watch case.
It converts fixed movement parameters into case geometry, clearance, and interface requirements, forming a practical application of HorologyCAD — Movement-Led Watch Case Engineering.
Movement Constraint Profile
Case design is defined only by parameters that affect integration:
- movement diameter: 27.4 mm
- movement height: ~5.3 mm
- stem height: ~2.25 mm
- automatic rotor system requiring dynamic clearance
These parameters establish the limits for:
- internal case diameter
- vertical stack height
- crown tube position
- case thickness
The movement defines all boundary conditions.
Constraint Structure
NH35 / NH36 integration is governed by four primary constraint domains:
Radial Constraint (Movement Diameter)
Movement diameter defines the minimum internal case diameter.
Radial behaviour is governed by Radial Clearance (Movement to Case Fit).
The case must provide:
- sufficient insertion clearance
- controlled lateral positioning
- compatibility with movement holder systems
NH35 systems commonly use holders rather than direct mounting.
Failure to control radial fit results in:
- lateral movement
- positional instability
- variation between assembled units
Axial Constraint (Movement Height)
Movement height defines the minimum internal depth of the case.
Vertical positioning is controlled by Axial Clearance (Vertical Spacing).
The axial stack includes:
- movement
- dial
- hand stack
- crystal underside
NH35 introduces a larger vertical envelope.
This reduces available design margin and increases sensitivity to variation.
Failure results in:
- hand-to-crystal contact
- excessive internal spacing
- unstable visual alignment
Stem Height Constraint (Crown Geometry)
Stem height fixes the vertical position of the crown interface.
The case must align the crown tube to this axis.
Deviation results in:
- off-axis loading
- increased friction in keyless works
- accelerated wear
Stem height cannot be modified.
All case geometry must adapt to it.
Rotor Clearance Constraint
The automatic rotor introduces a dynamic clearance requirement.
The case must provide:
- vertical clearance above the movement
- unobstructed rotational envelope
Failure results in:
- rotor contact with caseback
- reduced winding efficiency
- long-term mechanical damage
Rotor clearance must be validated under tolerance variation.
Internal Case Geometry
Internal geometry must support positioning, retention, and assembly.
Geometry is defined by Internal Case Geometry & Movement Cavity Sizing.
Requirements:
- cylindrical cavity sized to movement + clearance
- defined seating surface for movement holder
- clearance for dial feet and clamps
- uninterrupted insertion path
NH35 cases typically integrate holder-based positioning systems.
Geometry must support both static positioning and assembly motion.
Tolerance Behaviour
All dimensions vary under manufacturing conditions.
Tolerance interaction is defined by Full Tolerance Stack Example (Movement → Case → Crystal).
Critical relationships:
- movement height vs internal depth
- hand stack vs crystal clearance
- caseback position vs gasket compression
NH35 systems amplify variation due to larger dimensions.
Failure occurs when:
- clearance collapses under maximum condition
- compression exceeds limits under minimum condition
- alignment is lost across interfaces
Assembly Constraints
Assembly must remain physically executable.
Assembly behaviour is defined by Assembly Order & Constraints in Watch Case Design.
NH35-specific requirements:
- movement and holder inserted as a single unit
- crown and stem alignment during insertion
- access to securing features after placement
Failure results in:
- blocked assembly sequence
- forced insertion
- damage during installation
Assembly feasibility must be resolved during design.
Sealing System Interaction
Sealing depends on controlled compression and stable geometry.
Sealing behaviour is governed by Caseback Sealing System (Axial Compression Control).
NH35 introduces:
- increased stack variation
- larger compression sensitivity
- dependency on stable caseback positioning
Failure results in:
- under-compression → leakage
- over-compression → gasket deformation
Sealing must remain consistent across tolerance conditions.
Structural Requirements
Case structure must maintain dimensional stability under load.
Structural behaviour is defined by Case Rigidity vs Thinness Trade-Offs.
Requirements:
- sufficient wall thickness
- resistance to deformation
- stability of internal geometry
NH35 cases are typically thicker, but thickness alone does not guarantee rigidity.
Poor structural design results in:
- deformation under pressure
- loss of sealing compression
- misalignment of internal interfaces
Common Failure Points
Typical NH35 case failures include:
- crown misalignment due to incorrect stem positioning
- rotor contact with caseback under tolerance variation
- excessive internal clearance from poor holder control
- hand interference with crystal due to axial miscalculation
- sealing inconsistency due to uncontrolled compression
All originate from unresolved constraint interaction.
Design Strategy
Effective NH35 case design requires:
- defining radial clearance and holder integration
- controlling axial stack height
- aligning crown system from stem height
- validating tolerance stack under worst-case conditions
- ensuring assembly feasibility
- matching design to manufacturing capability
Design must resolve all constraints before final geometry is fixed.
Final Statement
The NH35 / NH36 defines a fixed set of dimensional and functional constraints.
A valid case design:
- maintains controlled clearance in all directions
- preserves alignment across all interfaces
- accommodates tolerance variation
- assembles without force
- performs under real operating conditions
The movement defines the system.
The case must be engineered to match it.