Single-Body vs Multi-Body Design

SINGLE-BODY DESIGN:
  One model body. All features build on it.

  Pros:
    - Simpler structure.
    - Faster CAD performance.
    - Easier to manage for small parts.

  Use when:
    - A bracket. A knob. A simple cap.
    - Anything that prints in one orientation.
    - Parts that don't mate with other CAD parts.

MULTI-BODY DESIGN:
  Multiple independent bodies in the same CAD file.
  Bodies can be separate or combined.

  Pros:
    - Design parts in context of how they fit together.
    - Test virtual assembly.
    - Maintain relationships between parts.

  Use when:
    - An enclosure (top + bottom + lid).
    - An assembly (multiple parts that mate).
    - A multi-material part (different bodies → different materials).

ASSEMBLIES (formal CAD concept):
  A separate file/document that contains multiple part files + their joints.

  Use when:
    - Many parts (10+).
    - Need to simulate motion (joints).
    - Sharing with team for parallel work.

  Fusion 360, OnShape, FreeCAD all support assemblies.

WHEN TO PROMOTE TO MULTI-BODY:

Trigger: you're sketching new geometry that depends on existing geometry.
  Example: a lid that must fit a specific box opening.

Approach:
  Single-body: build the lid with reference dimensions (manually).
  Multi-body: build the box, then build the lid IN CONTEXT of the box.

  Multi-body wins when the relationship is precise (lid must fit box).

WORKFLOW EXAMPLE:

ENCLOSURE WITH LID:

Single-body approach:
  - Design box.
  - Note inside dimensions.
  - Start NEW file. Design lid using those dimensions.
  - If box changes: manually update lid.

Multi-body approach:
  - Same CAD file.
  - Design box (Body 1).
  - Use 'Project' or 'Convert' to bring box's outer edges into a new sketch on top.
  - Design lid (Body 2) using projected edges as reference.
  - If box changes: lid updates automatically.

THIS IS THE POWER OF MULTI-BODY: PARAMETRIC RELATIONSHIPS BETWEEN PARTS.

BODY ORGANIZATION:

In Fusion 360: bodies are listed in the browser tree.
In OnShape: 'Parts' panel.
In FreeCAD: each body is a 'Body' object.

Naming bodies clearly: 'enclosure_bottom', 'enclosure_top', 'lid_screw_boss'.

VISIBILITY:

You can hide individual bodies.
Useful for: designing one part while others are hidden.

MERGING BODIES:

When two bodies combine into one final body:
  - Modify > Combine (Fusion).
  - Boolean Union (OnShape).
  - Boolean operation (FreeCAD).

PARTING LINES:

In multi-body: the line where bodies separate.
For printing: parting lines are where parts split.

Plan parting lines:
  - Where geometry is naturally divided (e.g., box vs lid).
  - Hidden in the assembled product.
  - Easy to assemble.