Assembly drawings are essential in various Kenyan professional fields where multiple components must be joined accurately to form a complete product. Whether in manufacturing equipment for a county referral hospital, assembling furniture for a university, or putting together machines used in agricultural cooperatives, clear assembly drawings ensure efficient construction and maintenance. This chapter focuses on producing assembly drawings with an emphasis on orthographic views and sectional views, which are crucial for illustrating how parts fit together.

6.1 Orthographic views of assembly drawings

Orthographic projection is the foundation of technical drawing used to represent three-dimensional objects in two dimensions. In the context of assembly drawings, orthographic views show different sides of a complete assembly to provide a clear understanding of how components are arranged and connected. Kenyan industries such as retail businesses assembling display units or banks organizing security systems rely on these views for accurate assembly and quality control.

6.1.1 First angle projection

First angle projection is one of the two main orthographic projection methods used globally and recognized by the British Standards (BS EN ISO 5456-2). It is the preferred method in many countries and sectors for assembly drawings because it shows the object as if placed in the first quadrant, behind the viewing planes.

Principles of first angle projection

• Object position: The object is imagined to be placed in the first quadrant between the observer and the plane of projection, meaning views are projected onto planes behind 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 shows the object from a direction perpendicular to the corresponding projection plane.
• Standard conventions: Line types follow BS EN ISO standards, with continuous thick lines for visible edges and dashed lines for hidden edges.
• Scale application: Common scales for assembly drawings are 1:1, 1:2, or 1:5, depending on the size of the assembly and drawing sheet.

Step-by-step procedure for first angle projection assembly drawing

1. Identify the object and its components: Understand the assembly and list all parts.
2. Select the main views: Usually the front, top, and one side view.
3. Draw the front view: Project the object’s front face with all visible details.
4. Project the top view below the front: Use perpendicular projectors from the front view to locate the top view.
5. Project the right side view to the left: Similarly, use projectors perpendicular to the front view.
6. Add hidden lines: Indicate internal features not visible in the views using dashed lines.
7. Dimension the views: Include all necessary dimensions for parts and assembly fit.
8. Add title block and notes: Include drawing title-scale, projection method symbol, and other relevant information.

Advantages of first angle projection in Kenyan professional fields

• Clear spatial relationship: The method provides a visual layout that is easy to interpret for assembly teams in hospitals assembling medical carts.
• Standardized practice: Many Kenyan TVET colleges teach this method, ensuring uniformity in technical communication.
• Ease of interpretation: Suitable for assemblies with complex internal parts, such as in agricultural machinery assembled by cooperatives.
• Compatibility: Aligns with British standards used in many Kenyan industries.
• Cost-effective: Simplifies production drawings reducing errors and rework in sectors like hotel furniture manufacturing.

6.1.2 Third angle projection

Third angle projection is widely used in the United States and increasingly in Kenya’s ICT and manufacturing sectors. It is recognized by BS EN ISO 5456-2 and involves placing the object in the third quadrant, with projections made onto planes in front of the object.

Characteristics of third angle projection

• Object position: The object is imagined in the third quadrant, behind the projection planes.
• View placement: 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: Views correspond to the observer’s perspective facing the object’s surfaces.
• Line conventions: Visible edges use thick continuous lines, hidden edges use dashed lines, consistent with ISO standards.
• Projection symbol: The third angle symbol is placed on the drawing to indicate the method used.

Procedure for creating third angle projection assembly drawings

1. Analyze the assembly: List all components and understand how they fit.
2. Determine the main views: Front, top, and right side.
3. Draw the front view: Show the assembly’s main face clearly.
4. Project the top view above the front: Use vertical projectors to position the top view.
5. Project the right side view to the right: Use horizontal projectors from the front view.
6. Include hidden details: Use dashed lines for features not visible externally.
7. Add dimensions: Provide measurements critical for assembly and verification.
8. Insert projection symbol and title block: Clearly indicate third angle projection and drawing details.

Benefits of third angle projection in Kenyan contexts

• Intuitive layout: Aligns with how many Kenyan workers visualize objects, useful in retail shelving assembly.
• Global acceptance: Facilitates partnerships with international suppliers and clients, such as in county government office equipment.
• Detailed representation: Captures complex assemblies with clarity, aiding maintenance of hospital equipment.
• Standard compliance: Meets ISO standards adopted by Kenyan manufacturing firms.
• Facilitates training: Easy for TVET students to learn and apply across multiple disciplines.

6.1.3 Comparison between first and third angle projection

6.1.4 Application of orthographic views in assembly drawings

Orthographic views are vital for clear communication in assembly tasks across Kenyan sectors. For example, a county referral hospital assembling a modular bed frame requires precise views to ensure correct fitting of parts. Similarly, a SACCO office installing a security barrier system depends on orthographic drawings to coordinate component assembly and installation. These views reduce errors, improve efficiency, and provide a permanent reference for maintenance.

Chapter Summary

This chapter focused on producing assembly drawings by emphasizing the importance of accurate orthographic views. It detailed the two primary projection methods used in assembly drawings: first angle projection and third angle projection, explaining their distinct placements and conventions. The chapter then explored sectional views, highlighting how they reveal internal features of components that are not visible in standard views. Additionally, it covered the preparation of parts lists, stressing the need for clear documentation of serial numbers, quantities, and recommended ratios to ensure proper assembly and inventory control. Understanding these elements is essential for creating comprehensive and precise assembly drawings that facilitate effective communication between designers, manufacturers, and technicians. The chapter combined theory with practical standards to equip learners with the skills necessary to produce technically sound and standardized assembly drawings.