The Sellita SW300-1 Case Core is a movement-fit CAD foundation for designing a watch case around the Sellita SW300-1 automatic movement.
It is not a complete exterior case design.
It is not a styling concept.
It is not a generic watch case CAD file.
The Case Core defines the internal movement-led architecture that a functional SW300-1 watch case must resolve before exterior styling, lugs, bezel shape, or final proportions are developed.
For the technical basis, start with Sellita SW300-1 Dimensions & Technical Data for Watch Case Design.
For the applied design guide, read Sellita SW300-1 Case Design Guide.
For the engineering constraints, read Sellita SW300-1 Case Design Constraints.
For the full site structure, return to the HorologyCAD homepage.
What the Sellita SW300-1 Case Core Defines
The Sellita SW300-1 Case Core defines the internal geometry required to build a case around the movement.
It focuses on:
movement location
movement cavity geometry
radial clearance
axial clearance
rotor clearance
movement seating
movement securing
caseback depth
stem axis position
crown tube relationship
dial-side stack control
date relationship where applicable
caseback interface
sealing allowance
tolerance planning
assembly logic
The purpose is to establish a reliable internal case foundation before external case design begins.
A watch case should not start as a shell.
It should start as a movement-fit system.
Supporting pages:
→ Movement to Case Fit
→ Internal Case Geometry & Movement Cavity Sizing
→ Watch Case Design System
Why the SW300-1 Needs a Movement-Fit Core
The SW300-1 is a slim 25.60 mm automatic movement.
Its case architecture must resolve automatic rotor clearance, thin-case axial planning, caseback depth, movement retention, crown and stem alignment, dial-side stack control, sealing geometry, and manufacturing tolerance.
A case designed around this movement must control:
movement fit
internal case geometry
radial clearance
axial clearance
rotor clearance
caseback depth
crown and stem alignment
dial-side stack relationship
date display relationship where applicable
movement retention
gasket compression
thin-case rigidity
wall thickness
manufacturing tolerance
A generic CAD case will not usually solve these relationships.
The Case Core exists to define the engineering foundation first, so the external case design can be developed around a controlled internal structure.
Supporting pages:
→ Movement-Led Watch Case Design
→ Watch Case Design Fundamentals
→ Movement Selection
Movement Diameter and Case Envelope
The SW300-1 has a 25.60 mm case-fitting diameter.
The Case Core does not simply copy this value into the case cavity.
It uses the movement diameter as the starting point for defining:
movement cavity diameter
movement holder allowance
radial clearance
movement seating surface
anti-rotation control
case wall relationship
tool access
assembly direction
The goal is controlled location.
The movement should fit without stress, but it should not float.
The internal case envelope must allow practical assembly while still controlling the movement position accurately.
Supporting pages:
→ Radial Clearance
→ Clearance vs Interference Fits
→ Watch Case Tolerances
Slim Movement Height and Axial Stack Control
The SW300-1 is commonly listed at approximately 3.60 mm high.
The Case Core does not treat movement height as final case thickness.
It defines the axial stack relationship between:
caseback
rotor clearance
movement height
movement seating
dial position
hand stack
crystal clearance
gasket compression
retaining geometry
The aim is to protect the movement while preserving the thin-case opportunity.
If axial stack control is ignored, the case may become too thick, too shallow, mechanically unsafe, structurally weak, or impossible to assemble correctly.
Supporting pages:
→ Axial Clearance
→ Movement Height vs Case Thickness
→ Axial Retention & Movement Stack Control
Rotor Clearance and Caseback Interface
The SW300-1 is an automatic movement, so the rotor envelope is a critical part of the Case Core.
The caseback cannot be designed only from external appearance.
It must protect rotor movement and allow for real mechanical variation.
The Case Core must account for:
rotor travel
rotor endshake
caseback internal depth
caseback machining tolerance
caseback gasket compression
assembly variation
shock behaviour
finishing allowance
Rotor interference can damage the movement, reduce winding efficiency, create noise, or leave visible wear.
For this reason, rotor clearance and caseback geometry are treated as core internal constraints, not late-stage adjustments.
Supporting pages:
→ Rotor Clearance Requirements for Automatic Movements
→ Watch Caseback Design and Fit
→ Water Resistance Engineering in Watch Cases
Crown and Stem Axis Control
The SW300-1 Case Core must define the crown and stem relationship from the movement datum.
The crown tube position should not be chosen by visual styling first.
The stem axis controls:
crown tube bore position
case wall opening
crown seat location
stem length behaviour
keyless works loading
crown sealing relationship
external crown placement
user winding and setting feel
Incorrect alignment can create rough winding, poor setting action, stem bending, crown tube misalignment, sealing problems, movement shift, or keyless works damage.
Because the SW300-1 is often used in slimmer cases, stem-height and crown-tube errors can become more difficult to absorb.
The Case Core therefore treats crown and stem alignment as an internal engineering constraint before external crown styling is considered.
Supporting pages:
→ Crown and Stem Alignment in Watch Cases
→ Crown Tube Positioning & Geometry
→ Crown Tube Installation & Tolerances
Dial-Side Stack Control
The SW300-1 dial-side stack must be defined before exterior case proportions are finalised.
The Case Core should account for:
dial thickness
dial seat height
dial support
date alignment where applicable
main hand stack height
hand-to-crystal clearance
rehaut height
crystal internal clearance
crystal retention geometry
bezel relationship
The movement may be slim, but the watch can still fail if the display stack is wrong.
If the dial-side stack is uncontrolled, the case may look correct externally but fail during assembly or use.
Supporting pages:
→ Dial to Crystal Clearance
→ Hand Stack Height and Clearance Requirements
→ Dial Seat Geometry
Date Configuration and Dial Relationship
The SW300-1 may be used in date or no-date configurations depending on the exact movement version and watch design.
Where a date display is used, the Case Core must account for the relationship between the movement, dial, date window, rehaut, and case opening.
It should define:
movement position
dial seating height
dial support
date window alignment
date wheel visibility
rotational control
rehaut relationship
crystal clearance
hand stack height
The date display is not only a dial-design detail.
It depends on movement location, dial seating, and case architecture.
If a no-date version or hidden-date construction is used, the Case Core should still reflect the exact movement selected.
Supporting pages:
→ Dial Seat Geometry
→ Watch Movement Dimensions Explained
→ Movement Selection
Movement Securing and Retention
The SW300-1 must be retained securely inside the case.
The Case Core must define how the movement is:
located radially
supported axially
prevented from rotating
protected from caseback pressure
kept aligned with the stem
kept aligned with the dial system
held during assembly
made serviceable
Movement securing may involve a holder, spacer, clamps, screws, retaining ledges, caseback control, or a combined strategy.
The important point is that retention is designed deliberately.
The movement should not be held by accidental compression or loose spacer geometry.
Supporting pages:
→ Movement Securing Methods
→ Axial Retention & Movement Stack Control
→ Internal Case Geometry & Movement Cavity Sizing
Caseback Interface and Movement Protection
The SW300-1 Case Core must define the caseback relationship for:
rotor clearance
movement protection
axial clearance
movement retention support
caseback gasket compression
caseback stiffness
service access
surface finish control
caseback seating accuracy
overall case thickness
The caseback cannot be reduced to a flat closing plate without considering rotor clearance, sealing behaviour, and movement protection.
It remains part of the internal engineering system.
Supporting pages:
→ Watch Caseback Design and Fit
→ Water Resistance Engineering in Watch Cases
→ Axial Retention & Movement Stack Control
Sealing and Gasket Planning
A Case Core must leave room for sealing systems.
The SW300-1 movement itself does not define water resistance.
The case architecture must provide:
caseback gasket geometry
crystal gasket geometry
crown sealing relationship
crown tube support
gasket compression allowance
surface finish control
seating accuracy
thread or press-fit support
assembly repeatability
Because the SW300-1 is commonly used for slim automatic case architecture, sealing space must be protected early.
Sealing cannot be added after the movement-fit architecture is already crowded.
Supporting pages:
→ Water Resistance Engineering in Watch Cases
→ Crystal Sealing System
→ Watch Caseback Design and Fit
Manufacturing and Tolerance Strategy
The SW300-1 Case Core must be manufacturable.
It is not enough for the CAD model to look correct on screen.
The geometry must account for:
CNC tool access
movement cavity accuracy
minimum wall thickness
crown tube bore alignment
flatness
concentricity
surface finishing allowance
gasket groove accuracy
caseback seating tolerance
crystal seat tolerance
movement holder tolerance
thread engagement
inspection requirements
A slim automatic case can be sensitive to tolerance errors.
Small dimensional errors can affect radial clearance, axial clearance, rotor clearance, crown alignment, dial height, hand clearance, gasket compression, and final assembly.
The Case Core should therefore define a tolerance-aware foundation that can survive machining, finishing, assembly, and use.
Supporting pages:
→ CNC Machining Constraints in Watch Cases
→ Watch Case Tolerances
→ Clearance vs Interference Fits
SW300-1 and ETA 2892-A2 Case Core Relationship
The SW300-1 and ETA 2892-A2 belong to the same slim 25.60 mm automatic movement category.
From a case-core perspective, they share similar design concerns:
movement cavity planning
radial clearance
axial clearance
rotor clearance
caseback depth
crown and stem alignment
movement securing
dial-side stack control
thin-case rigidity
tolerance strategy
However, the two movements should not be assumed identical in every practical detail.
A Case Core should always be validated against the actual movement used.
The SW300-1 is useful as a modern Sellita reference because it helps explain the slim automatic architecture also associated with ETA 2892-A2-style case design.
Supporting pages:
→ ETA 2892-A2 Case Core: Movement-Fit CAD System
→ ETA 2892-A2 Dimensions & Technical Data for Watch Case Design
→ ETA 2892-A2 Case Design Guide
SW300-1 and SW200-1 Case Core Relationship
The SW300-1 and SW200-1 are both Sellita automatic movements, but they create different case-core problems.
The SW200-1 belongs to the thicker standard automatic movement class.
The SW300-1 belongs to the slim automatic movement class.
This affects:
case thickness potential
caseback depth
rotor clearance planning
dial-side stack freedom
crown alignment sensitivity
thin-case rigidity
sealing geometry
manufacturing tolerance
A SW300-1 Case Core should not be treated as a SW200-1 Case Core with vertical height removed.
It should be developed as a slim automatic movement-fit foundation.
Supporting pages:
→ SW200-1 Case Core: Movement-Fit CAD System
→ SW200-1 Dimensions & Technical Data
→ SW200-1 Case Design Guide
What the Sellita SW300-1 Case Core Is Not
The Sellita SW300-1 Case Core is not:
a finished watch design
a complete exterior case shape
a lug design
a bezel styling package
a decorative concept
a generic case model
a production guarantee
a shortcut around engineering checks
It is the internal movement-fit foundation.
Exterior design can be developed around it, but the Case Core itself exists to solve the movement-led engineering problem first.
Why Generic CAD Cases Are Not Enough
Generic watch case CAD files often begin with an exterior shape.
They may show a case body, bezel, lugs, crown, or caseback, but they often do not fully resolve the movement-led constraints that determine whether the design will actually function.
Common missing elements include:
real movement cavity control
radial clearance planning
axial stack control
rotor clearance
stem height relationship
caseback depth
dial-side stack control
date alignment where applicable
gasket compression allowance
movement retention strategy
thin-case rigidity
tolerance behaviour
assembly order
For the SW300-1, these missing details matter because it is a slim automatic movement with rotor, caseback, crown, dial-side, and sealing constraints.
A generic case can look correct and still fail internally.
The Case Core solves the internal system first.
Supporting pages:
→ Why Most Watch Case Designs Fail
→ Failure Cascade Analysis
→ Design Validation Checklist
How the Case Core Supports Exterior Case Design
Once the SW300-1 Case Core is defined, the external design can be developed with better control.
The Case Core gives the designer a reliable foundation for:
case diameter decisions
case thickness decisions
lug architecture
bezel height
caseback shape
crown placement
crystal position
dial opening
rehaut geometry
water resistance planning
manufacturing review
This does not remove design freedom.
It protects it.
A designer can still develop different exterior styles, but those styles are built around a movement-fit foundation rather than guessed internal space.
Case Core Validation
Before a SW300-1 Case Core is treated as usable, it should be checked for:
movement fit
radial clearance
axial clearance
rotor clearance
caseback depth
crown and stem alignment
dial-side stack height
date display relationship where applicable
hand-to-crystal clearance
movement securing
thin-case rigidity
gasket compression allowance
caseback sealing geometry
crystal sealing geometry
crown sealing relationship
CNC manufacturability
wall thickness
tolerance stack behaviour
assembly order
service access
A Case Core that has not passed these checks is not ready to support exterior design or prototyping.
Supporting pages:
→ Design Validation Checklist
→ Watch Case Design Fundamentals
→ Movement-Led Watch Case Design
HorologyCAD Design Position
Within HorologyCAD, the Sellita SW300-1 Case Core represents the movement-led foundation for slim automatic case architecture.
It shows how a movement’s published dimensions must be translated into usable internal geometry before a complete case can be designed.
The case core is not the whole watch case.
It is the engineering foundation that helps the case become possible.
The SW300-1 creates the opportunity for slim modern automatic design, but the Case Core determines whether that opportunity becomes controlled, manufacturable, and assembly-ready.
For the broader framework, return to the HorologyCAD homepage.