Technical Drawing
Complete Notes — Easy English

Drawing Definition

Technical drawing is a precise way to show objects using lines, symbols, and dimensions.

Types of Technical Drawings

• Freehand Sketches: Quick ideas without instruments
• Mechanical Drawings: Precise with scales and instruments
• CAD Drawings: Created using computer software

Drawing Tools

• Pencils (HB, H, 2H for different line weights)
• Compass (circles and arcs)
• Ruler and scale (measurements)
• Set square (angles)
• Protractor (angle measurement)

Standards and Scales

• ISO Standards: International drawing standards
• Common Scales: 1:1 (full size), 1:2, 1:10, 2:1

Paper Sizes

Line Types and Uses

Line Conventions

• Horizontal: Drawn left to right
• Vertical: Drawn top to bottom
• Slanting: 45° angle
• Curved: Arc or smooth curves

Technical Lettering

• Height: 3.5mm for titles, 2.5mm for notes
• Style: Vertical or italic
• Spacing: Even gaps between letters

Lettering Practice

Practice capital and lowercase letters to develop consistent style.

Projection Concept

Orthographic projection shows 3D object in 2D using multiple views (front, top, side).

First Angle vs Third Angle

• First Angle: View opposite to quadrant (Europe)
• Third Angle: View in same quadrant (USA)

Standard Views

Hidden Lines

Dashed lines show features not visible in that view.

Projection Techniques

• Project vertically between front and top
• Project horizontally between front and side
• Use 45° line for profile

Dimensioning Rules

• Dimensions placed outside views
• Use thin lines for dimension lines
• Place dimension at midpoint of line
• Keep dimensions aligned
• Include units (mm, cm, inch)

Dimension Types

• Linear: Length, width, height
• Angular: Angles in degrees
• Radial: Radius or diameter

Dimensioning Standards

Best Practices

• Avoid dimension duplication
• Dimension related features together
• Use chain or baseline dimensioning

Common Symbols

• Ø: Diameter
• R: Radius
• □: Square
• ∠: Angle
• ∟: Perpendicular

Surface Finish Symbols

• Rough: Coarse surface
• Smooth: Fine surface finish
• Ra values: Surface roughness in micrometers

Welding Symbols

• Butt weld
• Fillet weld
• Lap weld
• Groove weld

Tolerance Symbols

CAD Software

• AutoCAD: Industry standard
• SolidWorks: 3D modeling
• CATIA: Advanced design
• LibreCAD: Free alternative

CAD Advantages

• Precision and accuracy
• Easy modifications
• Rapid prototyping
• 2D and 3D capabilities
• Database management

Basic CAD Tools

• Line tool: Draw straight lines
• Circle tool: Draw circles
• Rectangle tool: Draw rectangles
• Trim tool: Remove excess lines
• Offset tool: Parallel lines

Workflow

• Set up drawing (scale, units)
• Draw geometry
• Add dimensions
• Apply symbols
• Export/Print

Why Section Views?

Show interior features not visible in normal orthographic views.

Types of Sections

• Full Section: Complete cutting plane
• Half Section: Cut half the object
• Offset Section: Non-aligned cutting plane
• Broken Section: Remove portion

Section Lines (Hatching)

• 45° diagonal lines
• Thin, evenly spaced
• Different patterns for different materials

Section Plane Indication

• Show cutting line in view
• Label with A-A, B-B
• Arrow shows viewing direction

Material Representation

Detail Drawing Components

• Multiple orthographic views
• All necessary dimensions
• Surface finish symbols
• Tolerance information
• Assembly notes

Title Block Information

• Drawing number
• Title
• Scale
• Date
• Designer name
• Approver

Assembly Drawing

• Shows how parts fit together
• Part numbers and quantities
• Bill of Materials (BOM)
• Assembly sequence notes

Drawing Checklist

• All views clear and correct
• Dimensions complete and accurate
• Symbols properly applied
• Title block filled
• Notes and instructions clear
• Checked by qualified person

Documentation Standards

Follow ISO 128, BS 308 or relevant national standards.