Assembly drawings are fundamental in automotive engineering, serving as the blueprint for assembling complex automotive components into functional systems. These drawings enable engineers and technicians in Kenyan automotive workshops and manufacturing plants to visualize how parts fit and interact, ensuring accuracy, efficiency, and safety during assembly. Mastery of orthographic projections and sectional views in assembly drawings is essential for communicating design intent clearly and avoiding costly errors in production and maintenance.

6.1 Orthographic views of assembly drawings

Orthographic views are the backbone of technical communication in automotive engineering. They provide multiple perspectives of an assembly, allowing engineers and technicians to understand the spatial relationships and positioning of components without ambiguity. In Kenya’s automotive industry, adherence to correct orthographic projection methods ensures consistency and compliance with international standards, facilitating collaboration across design, manufacturing, and service teams.

Four orthographic views of a car (Source: 697c72e40165f702)

6.1.1 First angle projection

First angle projection is a method of orthographic projection widely used in many parts of the world, including Kenya’s automotive workshops and engineering colleges. It involves projecting views of an object onto planes that are conceptually placed between the observer and the object, resulting in a specific arrangement of views on the drawing sheet.

Principles of first angle projection

• Projection planes placement: The object is placed in the first quadrant, meaning the planes of projection lie between the observer and the object.
• View arrangement: The top view is placed below the front view, and the right side view is placed to the left of the front view.
• View orientation: Each view is a true orthographic projection, showing exact dimensions without distortion.
• Use in automotive assemblies: It is preferred in some automotive manufacturing firms for its straightforward layout, especially in component assembly instructions.
• Standard conventions: Conforms to ISO 5456-2 and BS EN ISO 5456-2 standards, which Kenyan institutions adopt for consistency.

Step-by-step procedure for constructing first angle projection views

1. Identify the principal views needed: Usually front, top, and side views showing critical assembly details.
2. Draw the front view: Position the object’s most characteristic face facing the observer and draw its outline to scale.
3. Project the top view: Project lines vertically downwards from the front view edges and replicate the outline of the top face.
4. Project the side view: Project lines horizontally leftwards from the front view edges to capture the side profile.
5. Arrange the views: Place the top view below the front view and the side view to the left, maintaining uniform spacing.
6. Add dimensioning and annotations: Include all necessary dimensions, notes, and symbols according to BS 8888 standards.

Advantages of first angle projection in automotive assembly drawings

• Clear spatial relationship: The positioning of views reflects actual spatial relationships, aiding comprehension.
• Conformance to international standards: Facilitates collaboration with global automotive suppliers.
• Simplicity in layout: Reduces confusion in interpreting the views, especially for new technicians.
• Effective for complex assemblies: Allows clear depiction of parts hidden in one view but visible in another.
• Widely taught in Kenyan technical institutions: Ensures graduates are proficient in this convention.

Common pitfalls when using first angle projection

• Misplacement of views: Placing views incorrectly can lead to misinterpretation of the assembly.
• Inconsistent scaling: Using different scales for different views can cause confusion.
• Omission of hidden lines: Failing to show hidden components reduces drawing clarity.
• Ignoring standard symbols: Non-compliance with BS or ISO symbols can lead to errors.
• Poor dimensioning: Overcrowding or missing dimensions hamper assembly accuracy.

6.1.2 Third angle projection

Third angle projection is the dominant orthographic projection method used in automotive engineering in Kenya, especially in international and local automotive firms following American and ISO standards. It places the object between the observer and the projection planes, resulting in a different arrangement of views on the drawing sheet compared to first angle projection.

Principles of third angle projection

• Projection planes placement: The object lies in the third quadrant, with the observer positioned between the object and the plane.
• View arrangement: The top view is placed above the front view, and the right side view is placed to the right of the front view.
• View orientation: Each view shows the true shape and size of the object as seen from that direction.
• Common usage in automotive: Preferred in many Kenyan automotive assembly manuals and design documents.
• Standard compliance: Adheres to ISO 5456-2 and BS EN ISO 5456-2, ensuring uniformity.

Step-by-step procedure for constructing third angle projection views

1. Select the main views: Front, top, and side views necessary to describe the assembly.
2. Draw the front view: Depict the most descriptive face of the object at the center of the workspace.
3. Project the top view: Project vertical lines upward from the front view edges to define the top face.
4. Project the side view: Project horizontal lines rightward from the front view edges to capture the side profile.
5. Arrange the views: Place the top view above the front view and the side view to the right, maintaining alignment.
6. Include dimensions and annotations: Add all relevant measurements, assembly notes, and symbols.

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

Benefits of third angle projection for automotive assemblies

• Intuitive layout: View positions align with the observer’s perspective, facilitating interpretation.
• Global acceptance: Widely used in automotive industries, supporting international collaboration.
• Facilitates complex assemblies: Clear depiction of spatial relationships and component details.
• Standardized symbols and notation: Ensures drawings meet Kenya Bureau of Standards requirements.
• Common in automotive training: Kenyan TVET institutions emphasize this method for practical relevance.

Challenges when applying third angle projection

• Misinterpretation by first angle users: Confusion arises if the projection method is not clearly indicated.
• Incorrect view placement: Leads to assembly errors if views are swapped.
• Scaling inconsistencies: Can mislead technicians about actual sizes.
• Inadequate dimensioning: Omitting critical dimensions affects assembly quality.
• Failure to show hidden components: Reduces the drawing’s usefulness in understanding internal features.

Chapter Summary

This chapter focused on producing assembly drawings, beginning with the use of orthographic views to represent complex objects accurately. It detailed the two main projection methods employed in assembly drawings: first angle projection and third angle projection, explaining their layout and application. The chapter then explored sectional views, highlighting their importance in revealing internal features of assembled components that are not visible in standard orthographic projections. Attention was given to the correct interpretation and drawing of these sections to enhance clarity. Finally, the chapter covered the preparation of parts lists, emphasizing the inclusion of serial numbers, quantities, and recommended ratios to organize components systematically. Together, these topics provide a comprehensive understanding of how to create precise and informative assembly drawings following accepted standards.