Orthographic drawings are fundamental in automotive engineering technology as they provide precise and clear representations of automotive components. These drawings enable engineers, technicians, and fabricators to visualize parts accurately for manufacturing, inspection, and maintenance. In Kenya’s automotive industry, adherence to international drawing standards ensures compatibility and quality across local workshops and global supply chains. This chapter focuses on producing orthographic drawings using first and third angle projections and mastering dimensioning techniques essential in automotive component detailing.

3.1 Orthographic Drawings

Orthographic drawings are the backbone of technical communication in automotive engineering. They translate three-dimensional automotive components into multiple two-dimensional views, enabling detailed analysis and fabrication. Kenyan automotive workshops and manufacturers depend on these drawings to ensure consistency and precision in vehicle part production and repair. This section covers the two principal projection methods used in orthographic drawings and their application in automotive contexts.

3.1.1 First Angle Projection

First angle projection is a method of orthographic drawing widely used in many countries including Kenya’s automotive sector for certain engineering documentation. It involves positioning the object between the observer and the plane of projection, which influences the layout of views on the drawing sheet.

Concept of First Angle Projection

• Object Positioning: In first angle projection, the object is placed in the first quadrant, meaning it lies between the observer and the plane of projection.
• View Arrangement: The views are arranged such that the top view appears below the front view, and the right side view appears on the left side of the front view.
• Projection Planes: Three primary planes are used: the horizontal plane, the vertical plane, and the profile plane, each capturing different views of the object.

A 3D isometric view and corresponding orthographic projections (front (Source: 697c72e40165f702)

• Image Formation: Each view is a true orthographic projection, showing the object’s features without distortion.
• Usage in Automotive Engineering: This method is useful when detailing components that require a specific orientation for assembly or inspection in workshops.

Step-by-Step Procedure for Drawing First Angle Projection

1. Identify the Views Required: Determine front, top, and side views essential for the component.
2. Draw the Front View: Sketch the front view to scale using standard line types as per BS 8888 or ISO 128.
3. Project the Top View Below the Front View: Using construction lines, project points from the front view vertically downward to locate the top view.
4. Project the Right Side View to the Left of the Front View: Project horizontal lines from the front view to the left to position the right side view.
5. Complete Details in Each View: Add all visible edges, hidden lines (dashed), and center lines using correct line conventions.
6. Check Alignment and Scale: Ensure that all views are correctly aligned and drawn to the same scale to maintain dimensional accuracy.

An isometric view and its corresponding orthographic projections (fron (Source: PLUMB 5 LEARNING GUIDE-1 (1))

Standards and Conventions for First Angle Projection

• Line Types: Solid thick lines for visible edges, dashed lines for hidden edges, and thin lines for dimensioning.
• Scale: Common scales include 1:1, 1:2, 1:5 depending on component size.

Wooden architect's scale ruler with measurement markings (Source: Wikipedia (Scale ruler))

• Title Block: Must include component name-scale, drawing number, and projection symbol (a truncated cone symbol indicating first angle).
• Projection Symbol Placement: Positioned in the title block or near the drawing border for clarity.
• Paper Size: Use standard sizes such as A3 or A4 as per ISO 5457 depending on component complexity.

Application Examples in Automotive Engineering

• Engine Component Drawings: First angle projection is used to detail cylinder head components, enabling clear visualization of ports and bolt patterns.
• Brake System Parts: Orthographic views help illustrate caliper shapes and piston arrangements for maintenance manuals.
• Transmission Gears: Gear profiles and shaft interfaces are clearly represented for manufacturing.

planetary transmission gear mechanism (Source: Wikimedia Commons)

• Chassis Components: Suspension arm drawings utilize first angle to show mounting points and cross-sections.
• Electrical Connectors: Housing and pin layouts are depicted to assist in assembly.

circular electrical connector with multiple pins (Source: Wikimedia Commons)

3.1.2 Third Angle Projection

Third angle projection is the preferred orthographic method in many automotive engineering environments in Kenya, especially in manufacturing and export-oriented workshops. It places the plane of projection between the observer and the object, affecting the layout of views.

Concept of Third Angle Projection

• Object Positioning: The object is located in the third quadrant, with the plane of projection between the observer and the object.
• View Arrangement: The top view is placed above the front view, and the right side view appears on the right side of the front view.
• Projection Planes: Similar to first angle but with different spatial relationships yielding a distinct layout.
• Image Formation: Maintains true scale and shape representation without distortion.
• Automotive Relevance: Common in Kenyan automotive manufacturing plants due to global alignment with ISO and BS standards.

Step-by-Step Procedure for Drawing Third Angle Projection

1. Determine Necessary Views: Identify front, top, and side views based on component complexity.
2. Draw the Front View: Begin by sketching the front view accurately to scale.
3. Project the Top View Above the Front View: Project vertical construction lines upwards to locate the top view.
4. Project the Right Side View to the Right of the Front View: Extend horizontal construction lines to the right side for the side view.
5. Detail Each View: Include visible edges, hidden lines, and center lines using appropriate line styles.
6. Verify Alignment and Scale Consistency: Confirm all views are aligned and uniformly scaled.

Standards and Conventions for Third Angle Projection

• Line Types: Use thick continuous lines for visible edges, dashed lines for hidden details, and thin continuous lines for dimensions.
• Scale: Select scale based on component size and drawing sheet; typical scales are 1:1, 1:2, 1:10.
• Title Block Requirements: Must include drawing title-scale, date, and the third angle projection symbol (a truncated cone symbol with the larger end on the left).
• Projection Symbol Placement: Clearly shown in the title block or drawing border.
• Paper Size and Orientation: Follow ISO 5457 recommendations for A3 or A4 sheets with landscape or portrait orientation as appropriate.

Application Examples in Automotive Engineering

• Fuel Injection Components: Detailed views of nozzles and valves for manufacturing precision.
• Exhaust System Parts: Multiple views illustrate bends and flange details.
• Steering Mechanism Components: Orthographic projections show shaft profiles and mounting brackets.
• Cooling System Parts: Radiator and pump housing drawings aid assembly and repair.
• Electrical System Housings: Battery terminal covers and fuse boxes detailed for production.

Chapter Summary

This chapter focused on producing orthographic drawings of components, beginning with an exploration of orthographic projection methods, specifically first angle and third angle projections, which are fundamental for representing three-dimensional objects in two dimensions. It emphasized the importance of accurate dimensioning to convey the exact size and specifications of components clearly. The chapter also covered sectional views, which reveal internal features by cutting through objects to improve understanding of complex parts. Additionally-free hand sketches were discussed as an essential skill for quick and effective communication of ideas, with attention given to geometric forms and the proper use of drawing tools and equipment. The final section highlighted sketching mechanical components free hand, ensuring clarity and precision even in informal settings. Overall, the chapter integrated theory with practical drawing techniques to build a strong foundation in technical drawing for component production.