Assembly drawings are vital in multiple Kenyan professional fields as they provide clear visual instructions for assembling components into a complete product or system. Whether in a hospital setting assembling medical equipment, a retail business managing product packaging, or a county government office coordinating infrastructure components, accurate assembly drawings ensure efficiency and reduce errors. This chapter focuses on the standardized methods used to represent assemblies through orthographic views and sectional views, which facilitate clear communication among designers, manufacturers, and technicians.

6.1 Orthographic views of assembly drawings

Orthographic projection is the cornerstone of technical drawing in Kenya’s diverse industries such as education, agriculture, and financial services, where clear communication of spatial relationships is essential. Orthographic views in assembly drawings allow professionals to visualize each component’s position and how parts fit together without ambiguity. Understanding the two main projection methods, first angle and third angle projection, is crucial for creating and interpreting accurate assembly drawings compliant with international and Kenyan standards.

6.1.1 First angle projection

First angle projection is a widely recognized method in technical drawing used to represent three-dimensional assemblies on two-dimensional planes. It is commonly applied in Kenyan manufacturing and county government projects, where conformity to British Standards (BS EN ISO 128) is often required.

• Definition: In first angle projection, the object is conceptually placed in the first quadrant, meaning the object lies between the observer and the projection planes. The views are projected onto planes behind the object.
• View arrangement: The top view is placed below the front view, the right side view is placed on the left of the front view, and the left side view is placed on the right. This arrangement is opposite to third angle projection.
• Line conventions: Visible edges use continuous thick lines, hidden features use dashed lines, and centerlines use alternating long and short dashes according to BS EN ISO 128.
• Applications: First angle projection is preferred in many Kenyan educational institutions and agricultural equipment design projects due to its clarity in representing internal features.
• Identification symbol: The first angle projection symbol is a truncated cone, used in title blocks to indicate projection type on drawings.

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

1. Start with the front view: Draw the most descriptive face of the assembly, showing overall height and width.
2. Project the top view below the front view: From the front view, project vertical construction lines downwards to position the top view.
3. Project the side views horizontally: Project horizontal lines from the front view to the left and right to place the right and left side views respectively.
4. Draw hidden detail lines: Use dashed lines to illustrate features not visible in the current view.
5. Add centerlines: Use alternating long-short dashes to indicate symmetry axes or holes.
6. Include dimensioning and annotations: Provide all necessary measurements and notes for assembly.

6.1.2 Third angle projection

Third angle projection is the dominant projection method in Kenya’s commercial design sectors such as banking hardware layout and hospital equipment assembly, following American and ISO standards. It offers a different spatial relationship compared to first angle projection, which affects the placement of views.

• Definition: In third angle projection, the object is conceptually placed in the third quadrant, meaning the projection plane lies between the observer and the object.
• View arrangement: The top view is placed above the front view, the right side view is placed on the right of the front view, and the left side view on the left. This layout aligns intuitively with how the object is viewed.
• Line type standards: Same as first angle projection, adhering to BS EN ISO 128 for line thickness and style.
• Applications: Third angle projection is favored in Kenyan ICT hardware assembly drawings and retail packaging design, facilitating straightforward interpretation.
• Identification symbol: The third angle projection symbol is also a truncated cone, but oriented differently from the first angle symbol and displayed in the drawing’s title block.

Step-by-step construction procedure for a third angle projection assembly drawing

1. Begin with the front view: Sketch the main face of the assembly showing height and width.
2. Project the top view above the front view: Project vertical construction lines upwards from the front view to place the top view.
3. Project side views horizontally: Project horizontal lines to the right and left for the right and left side views respectively.
4. Draw hidden detail lines: Use dashed lines for concealed features in each view.
5. Mark centerlines: Use alternating long and short dashes to highlight axes of symmetry or cylindrical features.
6. Add dimensions and notes: Clearly dimension all relevant features and provide assembly instructions.

Chapter Summary

This chapter focused on producing assembly drawings, beginning with the use of orthographic views to represent different components clearly. It explained the two main projection methods: first angle projection and third angle projection, detailing their layout conventions and applications. The chapter then covered sectional views, emphasizing their importance in revealing hidden internal features of assembled parts for better understanding and accuracy. Additionally, the creation and interpretation of parts lists were discussed, highlighting how to organize components by serial number, quantity, and recommended ratios to ensure clarity in assembly instructions. The integration of these elements ensures that assembly drawings communicate comprehensive and precise information necessary for manufacturing and construction. Mastery of these techniques supports the effective visualization and documentation of complex assemblies in technical drawing.