---
title: "CAD software modules: part, assembly, drafting"
subject: "Computer Aided Design"
chapter: 1
key: "semester_4/computer_aided_design:cad-software-modules"
source: https://www.bctengineer.com/q/semester_4/computer_aided_design/cad-software-modules
site: BCT Engineering
---

# CAD software modules: part, assembly, drafting

Computer Aided Design · Chapter 1: Introduction

- Asked in: year not given, 5 marks
- Video: [CAD Assembly modeling module overview (Computer Aided Design)](https://www.youtube.com/watch?v=iGl7jLqA8vc) — Newtonian World
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/computer_aided_design/cad-software-modules
- Whole chapter: https://www.bctengineer.com/md/semester_4/computer_aided_design/chapter-1

## Question

Explain the main modules of a typical 3D CAD software package: part module, assembly module and drafting module. How are the three modules related?

## Short answer

Part module builds a single parametric solid from sketches and features. Assembly module positions parts with mating constraints, checks interference and creates BOM. Drafting module generates 2D drawings. They are associative through a common database, so changes in any module update the assembly and drawing automatically.

## Answer

A modern CAD package is organised into modules that work on one common database.

#### Part module
Used to create a single component. The designer draws a 2D sketch, adds dimensions and constraints, and turns it into a 3D solid with features such as extrude, revolve, sweep, loft, hole, fillet and chamfer. The result is a parametric model: changing a dimension rebuilds the part. Material and mass properties are attached here.

#### Assembly module
Brings several parts or sub-assemblies together and positions them using **mating constraints** (coincident, concentric, parallel, distance, angle). It supports interference checking, exploded views, motion study and a bill of materials (BOM). Assemblies can be built bottom-up (existing parts) or top-down (new parts designed in place).

#### Drafting module
Generates 2D engineering drawings from the 3D model or assembly: orthographic, sectional, auxiliary and detail views, dimensions, tolerances, notes, title block, balloons and BOM table.

#### Relationship
```text
   PART  ---->  ASSEMBLY  ---->  DRAWING
    ^              |                |
    +-- changes flow both ways ----+
```
The modules are **associative**: if a dimension in the part module is changed, the assembly and the drawing update automatically. This avoids inconsistency between the model and the drawings. Other modules (sheet metal, surfacing, simulation, CAM) use the same model.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which feature is characteristic of the part module?
   A. Mating constraints between components
   B. Balloons and title block
   C. Sketch, dimensions and features such as extrude and revolve to form a parametric solid
   D. Interference checking between parts
   Answer: C. The part module turns a dimensioned 2D sketch into a 3D parametric solid using features. (Key point: Part module)

2. What are mating constraints used for?
   A. Defining fillet radii
   B. Creating section views
   C. Setting the material of a part
   D. Positioning parts relative to each other in an assembly
   Answer: D. Mates such as concentric, coincident and distance locate parts relative to each other. (Key point: Assembly module)

3. A dimension is changed in the part module. What happens in an associative CAD package?
   A. Assembly and drawing update automatically
   B. Nothing; the drawing must be redrawn by hand
   C. Only the assembly updates
   D. Only the part is saved with the new value
   Answer: A. The modules share one database and are associative, so changes flow to assembly and drawing, keeping them consistent. (Key point: Associativity)

## Related in Computer Aided Design

- [Assembly constraints and tolerance fit calculation](https://www.bctengineer.com/question.md?key=semester_4%2Fcomputer_aided_design%3Aassembly-constraints-tolerance-fit) — Computer Aided Design, chapter 5

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