Orthographic drawings are fundamental in Kenya’s diverse professional fields for accurately representing three-dimensional objects on two-dimensional media, facilitating clear communication across departments and sectors. Whether in hospital equipment design, agricultural machinery maintenance, or business infrastructure layout, orthographic projections ensure all stakeholders understand component details without ambiguity. This chapter focuses on producing orthographic drawings using standard projection methods and correct dimensioning to meet Kenyan and international standards, essential skills for diploma-level TVET students.

3.1 Orthographic Drawings

Orthographic drawings translate complex components into multiple flat views, enabling precise visualization and measurement. In Kenya, professionals from healthcare to county government planning rely on these drawings to convey technical details clearly and uniformly. Understanding projection methods and their conventions is crucial for creating standardized drawings accepted in all sectors.

3.1.1 First Angle Projection

First angle projection is a method of orthographic projection commonly used internationally and recognized under ISO standards, including in Kenyan technical documentation. It involves projecting views onto planes located between the observer and the object, producing views arranged differently from third angle projection. This technique is especially prevalent in European and some African technical environments.

Principles of First Angle Projection

• Projection Plane Positioning: The object is placed in the first quadrant, meaning the projection plane lies between the observer and the object, causing images to be projected through the object onto the plane.
• View Arrangement: The top view is placed below the front view, the right side view is placed on the left side, and the left side view is placed on the right side of the front view.
• View Orientation: Each view is a direct orthogonal projection, meaning views show true dimensions without perspective distortion.
• Symbol Usage: The first angle projection symbol, standardized by BS EN ISO 5456-2, must appear in the title block for clarity.
• Application Context: Often used in sectors where ISO standards are dominant, such as county government infrastructure projects or hospital equipment design.

Step-by-Step Procedure for First Angle Projection Drawing

1. Identify the Object: Examine the component to be drawn, noting its shape, features, and dimensions.
2. Select Views: Choose principal views, front, top, and side, that best describe the object’s shape.
3. Establish the Drawing Layout: Place the front view centrally on the drawing sheet.
4. Project the Top View: Draw the top view directly below the front view, aligning edges vertically.
5. Project the Side View: Draw the right side view to the left of the front view, aligning edges horizontally.
6. Add Details and Hidden Lines: Include all necessary lines such as edges, holes, and hidden features using appropriate line types.
7. Insert the First Angle Projection Symbol: Place the standard symbol in the title block or drawing corner.
8. Review for Completeness: Verify all views align correctly and accurately represent the object.

Comparison with Third Angle Projection

• View Placement: First angle places the top view below the front; third angle places it above. Similarly, first angle puts the right side view on the left; third angle on the right.
• Standard Usage: First angle is ISO-preferred, common in Kenya’s international trade and government sectors; third angle is dominant in the USA and some private companies.
• Symbol Recognition: Each projection uses a distinct symbol, aiding in clear communication.
• Interpretation Ease: Users familiar with one method may misinterpret drawings in the other, necessitating clear labeling.
• Suitability: Selection depends on client or regulatory requirements; Kenyan SACCOs managing international equipment imports often specify projection method.

Common Mistakes in First Angle Projection

• Incorrect View Placement: Mixing positions of side and top views leads to confusion and errors.
• Omission of Projection Symbol: Without the symbol, viewers may misinterpret the projection method.
• Misalignment of Views: Views not properly aligned cause dimensional inaccuracies.
• Inconsistent Line Types: Using incorrect line weights or types reduces clarity.
• Neglecting Hidden Detail Lines: Omitting hidden lines hides important features, affecting manufacturing or maintenance.

3.1.2 Third Angle Projection

Third angle projection is widely used in Kenya’s manufacturing and construction industries, especially in firms trading with or adopting American standards. It involves projecting views onto planes behind the object relative to the observer, resulting in a different arrangement of views compared to first angle projection.

Principles of Third Angle Projection

• Projection Plane Positioning: The object lies in the third quadrant; the projection plane is behind the object from the observer’s perspective.
• View Arrangement: The top view is placed above the front view; the right side view is placed on the right side of the front view.
• View Orientation: Orthogonal views preserve true dimensions without perspective distortion.
• Use of Standard Symbol: The third angle projection symbol must be included for clarity, per BS EN ISO standards.
• Typical Industry Use: Common in Kenyan retail business product design and county government civil works drawings.

Step-by-Step Procedure for Third Angle Projection Drawing

1. Analyze the Object: Understand the component’s geometry and features.
2. Determine Principal Views: Select front, top, and side views that best reveal the object’s form.
3. Prepare Drawing Sheet: Place the front view centrally on the sheet.
4. Draw the Top View: Position the top view directly above the front view, aligning edges vertically.
5. Draw the Side View: Place the right side view to the right of the front view, aligning edges horizontally.
6. Add Details and Hidden Lines: Include all edges, holes, and internal features with appropriate line types.

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

1. Insert Third Angle Projection Symbol: Place the symbol clearly on the drawing.
2. Verify Accuracy and Completeness: Check alignment and details for correctness.

Advantages of Third Angle Projection in Kenyan Context

• Clarity for Local Manufacturing: Many Kenyan workshops and fabrication units are trained in third angle projection, easing communication.
• Compatibility with American Equipment: Kenyan hospitals and schools importing US-made equipment benefit from this method.
• Standardization: Facilitates uniformity in drawings across sectors using this projection.
• Ease of Interpretation: Logical placement of views corresponds to the object’s actual spatial orientation.
• Widely Taught: Most TVET colleges in Kenya emphasize third angle projection, supporting workforce readiness.

Challenges and Solutions in Third Angle Projection

Challenges

• Confusion with First Angle Projection: Learners often mix methods, producing incorrect views.
• Inconsistent Use of Symbols: Omitting or misplacing the projection symbol causes misinterpretation.
• Alignment Errors: Misaligned views lead to measurement and fabrication mistakes.
• Improper Line Types: Using incorrect line weights reduces drawing legibility.
• Inadequate Detailing: Failure to show hidden or sectional views limits drawing usefulness.

Solutions

• Clear Training on Differences: Emphasize distinctions between first and third angle in coursework.
• Mandatory Symbol Inclusion: Enforce symbol placement in all drawings.
• Use of Drawing Templates: Employ templates with predefined view positions to ensure alignment.
• Standardized Line Type Usage: Provide students with line type charts and enforce standards.
• Comprehensive Detailing Practices: Teach importance of hidden lines and sectional views for clarity.

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 essential for accurately representing objects in two dimensions. It then detailed the principles of dimensioning, emphasizing the correct placement and clarity of measurements to ensure precise communication in technical drawings. The use of sectional views was covered to illustrate internal features of components that are not visible from the outside, enhancing the understanding of complex parts. The chapter also introduced free hand sketches as a valuable skill for quickly conveying ideas, starting with basic geometric forms and progressing to the use of appropriate tools and equipment. Finally, it discussed sketching mechanical components, highlighting the importance of accuracy and neatness for effective technical communication. Together, these topics provide a comprehensive foundation for creating clear, standardized, and informative technical drawings.