How Engineering Drawings Differ from CAD

Engineering drawings and CAD (Computer-Aided Design) are both used to design and manufacture products, but they differ significantly in format, creation, and application. This guide explains the key differences to help you understand which is best for your project.

What are These Things?

Engineering drawings are 2D technical illustrations on paper or digital formats, using lines, symbols, and dimensions to specify a part’s size and shape.

CAD is a computer-based design tool that creates 3D models or 2D drawings of parts, allowing users to visualize and manipulate designs from any angle.

Big Differences Table

1. They Look Different

Engineering drawings are 2D, showing multiple views (top, side, front) with:

• Solid lines for visible edges
• Dashed lines for hidden edges
• Dot-dash lines for centerlines

CAD creates 3D models that can be:

• Rotated to view from any angle
• Sliced to see internal features
• Measured with precision

Precision CNC machining often relies on CAD models for accurate production.

2. Making Changes

Engineering drawings are labor-intensive to revise:

• Require manual erasing or redrawing
• Time-consuming, increasing error risk
• Difficult to distribute updated versions

CAD allows quick edits:

• Modify designs with clicks
• Automatically saves revision history
• Shares updates instantly via digital platforms

This is why 5-axis machining shops prefer CAD files for efficiency.

3. How Exact They Are

Engineering drawings are prone to:

• Human errors in measurements
• Physical damage (smudges, tears)
• Difficulty depicting tiny details

CAD ensures high precision:

• Computer-calculated measurements
• Zoomable to microscopic levels
• Accurate representation of complex geometries

4. Real Stories

Story 1: Fixing a Plane

Boeing’s 787 Dreamliner used CAD, reducing:

• Assembly errors by 40%
• Production time by 30%
• Ensuring parts fit perfectly on the first try

Story 2: Fixing Old Church

Restoring Notre-Dame after its fire relied on old engineering drawings, leading to:

• 6-month delays due to inaccuracies
• Errors in measurements requiring rework
• Extensive remeasuring of components

5. Who Uses What

Engineering drawings dominate in:

• Construction (45% of projects)
• Plumbing systems (30%)
• Legacy manufacturing (25%)

CAD is prevalent in:

• Automotive (70% of designs)
• Aerospace (80%)
• Motorsports (90%)

CNC turning shops increasingly rely on CAD for precision.

6. Working With Others

Engineering drawings hinder collaboration:

• Limited to single paper copies
• Require physical mailing or faxing
• Susceptible to loss or damage

CAD enables seamless collaboration:

• Multiple users can access simultaneously
• Files shared via email or cloud
• Secure and durable digital format

7. Cost Differences

Engineering drawings have low startup costs:

• Basic tools (pencils, rulers): $200-$500
• No need for advanced hardware
• Higher labor costs due to time

CAD has higher startup costs:

• Software licenses: $1,500-$5,000
• Requires powerful computers
• Saves time and labor in the long run

8. Time to Make

Engineering drawings take 8-10 hours for a simple part due to manual drafting.
CAD reduces this to 2-4 hours with automation, saving:

• 60-70% on revisions
• 25% on long-term costs

9. Making Real Parts

Engineering drawings require:

• Manual interpretation by machinists
• Setup of machines based on readings
• Risk of misinterpretation

CAD integrates with manufacturing:

• Direct communication with CNC machines
• Eliminates human reading errors
• Ensures consistent part production

CNC prototype machining benefits greatly from CAD integration.

10. How They Help Design

Engineering drawings slow design:

• Require redrawing for each change
• Difficult to verify part fitment
• Limited simulation capabilities

CAD accelerates design:

• Instant updates to test ideas
• Virtual assembly to check fit
• Simulations for performance testing

11. Standards They Follow

Engineering drawings adhere to:

• ASME Y14.5 (U.S. standard)
• ISO 128 (international standard)
• Strict rules for lines, symbols, and annotations

CAD enforces standards automatically:

• Flags design errors
• Auto-corrects minor issues
• Ensures compliance with manufacturing tolerances

12. What’s Better When

Engineering drawings are ideal for:

• Regulatory submissions requiring paper
• Remote areas without computers
• Quick, rough sketches

CAD excels for:

• Complex geometries
• Frequent design iterations
• Global team collaboration

13. Mixing Both Ways

Modern workflows combine both:

• Create CAD models for design and testing
• Generate engineering drawings from CAD for documentation
• Use both to meet diverse project needs

This approach is common in precision CNC machining shops.

14. What’s Coming Next

Emerging technologies are shaping both:

• AI: Automates design optimization
• Model-Based Definition (MBD): Embeds all data in 3D models, reducing reliance on drawings
• VR/AR: Visualizes designs in real-world contexts

15. Questions People Ask

Sum Up

Engineering drawings are best for:

• Simple projects
• Regulatory compliance
• Low-tech environments

CAD is superior for:

• Complex designs
• Rapid iterations
• Collaborative workflows

Today, most industries favor CAD for its efficiency, but engineering drawings remain relevant for specific applications.