Orthographic drawings form a fundamental part of technical drawing used across various Kenyan industries such as county government offices, hospitals, retail businesses, and agricultural cooperatives. These drawings enable professionals to represent three-dimensional objects in two dimensions, facilitating clear communication between designers, manufacturers, and clients. Mastery of orthographic projection techniques and accurate dimensioning is essential for producing precise, standardized drawings that meet Kenya Bureau of Standards (KEBS) requirements and international conventions. This chapter focuses on producing orthographic drawings of components, emphasizing projection methods and dimensioning principles applicable across multiple professional fields.

3.1 Orthographic drawings

Orthographic drawings are a cornerstone in technical communication, providing detailed views of objects without distortion. In Kenya’s diverse professional environments, from university laboratories to SACCO offices, these drawings ensure accurate interpretation of component designs for manufacturing, construction, or quality control. Understanding the two primary projection conventions, first angle and third angle projection, and their correct application is critical to avoid costly errors and miscommunication.

3.1.1 First angle projection

First angle projection is a method widely used in many countries, including Kenya, especially in educational institutions and manufacturing workshops. It involves projecting the object onto planes placed between the observer and the object itself, resulting in views arranged in a specific layout.

Meaning of first angle projection

• Definition: First angle projection places the object between the observer and the projection plane, so the views are projected onto planes behind the object.
• View arrangement: The top view is drawn below the front view, and the right-side view is drawn to the left of the front view.
• Projection planes: The object is conceptually enclosed in six planes: front, top, bottom, left, right, and rear.
• Image orientation: Views appear reversed compared to the object’s actual orientation, requiring careful interpretation.
• Symbol identification: The first angle projection symbol, standardized by ISO and BS, is used on drawings to indicate this method.

Significance in Kenyan professional settings

• Standardized communication: Ensures consistency across industries like county hospitals and agricultural equipment manufacturing.
• Compatibility with KEBS: Aligns with Kenya Bureau of Standards and ISO drawing conventions used in training and workplaces.
• Ease of interpretation: Familiarity with this method reduces errors during fabrication or assembly.
• Widely taught: Preferred in many Kenyan TVET colleges, supporting foundational learning.
• International relevance: Used in countries with similar drawing standards, aiding Kenyan exports and collaborations.

Construction procedure for first angle projection

1. Select the object to be drawn and identify the front face.
2. Draw the front view on the drawing sheet, representing the object’s front face as seen by the observer.
3. Project the top view below the front view by projecting vertical lines downward from the front view’s outline.
4. Project the right side view to the left of the front view by drawing horizontal projection lines leftwards.
5. Complete other views (left, bottom, rear) if necessary, following the same projection logic.
6. Label all views clearly and include the first angle projection symbol at the title block or near the drawing.

Common mistakes when applying first angle projection

• Incorrect view placement: Confusing the left and right side views, causing misinterpretation.
• Omitting projection symbol: Leading to ambiguity about the projection method used.
• Inconsistent scale: Using different scales for views without indication.
• Misaligned projections: Failing to align views properly along projection lines.
• Poor dimensioning: Not adapting dimensions to the view’s orientation and scale.

3.1.2 Third angle projection

Third angle projection is the preferred method in several countries and increasingly adopted in Kenyan industries such as retail business equipment design and university laboratory apparatus fabrication. It projects views onto planes placed behind the observer, providing a more intuitive layout.

Meaning of third angle projection

• Definition: The projection plane is placed between the observer and the object, so views are projected onto planes in front of the object.
• View arrangement: The top view is drawn above the front view, and the right-side view is drawn to the right of the front view.
• Projection planes: The object is conceptually surrounded by projection planes where views are mapped.
• Image orientation: Views correspond more closely to the actual orientation of the object.
• Symbol identification: The third angle projection symbol, standardized by ISO and BS, is used to mark drawings employing this method.

Importance in Kenyan professional contexts

• Clearer visualization: Used in sectors like county government offices for architectural and equipment layouts.
• International standards: Aligns with American and ISO standards, facilitating global trade and collaboration.
• Training relevance: Increasingly taught in TVET institutions to prepare students for diverse workplace demands.
• Reduced confusion: The intuitive layout helps non-technical stakeholders understand drawings better.
• Cross-sector application: Useful in hospitality industry equipment design and agricultural machinery parts.

Construction procedure for third angle projection

1. Identify the object and select the front face for the primary view.
2. Draw the front view on the drawing sheet.
3. Project the top view above the front view by projecting vertical lines upward from the front view’s outline.
4. Project the right side view to the right of the front view by projecting horizontal lines rightwards.
5. Add other views as needed using the same projection principles.
6. Insert the third angle projection symbol in the drawing title block or near the main views.

Differences between first and third angle projection

Chapter Summary

This chapter explored the production of orthographic drawings of components, beginning with the fundamental principles of orthographic projection. It detailed the differences and applications of first angle projection and third angle projection, emphasizing their correct usage in technical drawing. The chapter then covered dimensioning techniques, highlighting how accurate measurements and clear annotations are essential for conveying precise information on drawings. Sectional views were introduced as a method to reveal internal features of components that are not visible in standard views. The importance of freehand sketches was discussed, focusing on the ability to quickly represent ideas and concepts. This included practice with geometric forms, the use of basic drawing tools and equipment, and sketching mechanical components to build foundational drawing skills. Overall, the chapter provided a comprehensive guide to creating clear, accurate, and informative technical drawings through a combination of projection methods, dimensioning, sectional views, and sketching techniques.