Orthographic drawings are fundamental in technical communication across all professional fields in Kenya. They allow clear, precise representation of components and objects, essential for manufacturing, construction, healthcare equipment design, and many other sectors. This chapter equips students with skills to produce accurate orthographic projections and apply correct dimensioning techniques, ensuring that drawings serve as reliable guides in diverse workplace settings such as county hospitals, universities, banks, and agricultural cooperatives.

3.1 Orthographic drawings

Orthographic drawings provide a method to represent three-dimensional objects in two dimensions, showing multiple views to convey complete shape and size information. Mastery of orthographic projection techniques is critical across Kenyan industries, from designing medical devices in hospitals to planning retail store layouts. This section covers the two primary projection methods used in Kenya and internationally: first angle and third angle projection.

3.1.1 First angle projection

First angle projection is a standardized method of orthographic drawing widely used in many countries including Kenya. It is especially favored in architectural and manufacturing sectors within county government offices and construction firms.

Meaning of first angle projection

1. Definition: First angle projection places the object between the observer and the plane of projection, meaning views are projected onto planes behind the object.
2. View arrangement: The top view is placed below the front view, and the left side view is placed on the right side of the front view.
3. Projection planes: Three mutually perpendicular planes are used: frontal, horizontal, and profile planes.
4. Image formation: Each view is a true shape projection onto its respective plane.
5. Symbol identification: The first angle projection symbol consists of a truncated cone with the small end facing left.

Steps to construct first angle projection

1. Identify the object’s front view: Determine the most characteristic face of the object to serve as the front.
2. Project the top view: Draw the horizontal plane below the front view and project points vertically downward.
3. Project the side view: Draw the profile plane to the right of the front view and project points horizontally to the right.
4. Use orthogonal projection lines: Ensure projection lines are perpendicular to the viewing planes.
5. Complete hidden lines: Represent hidden edges using dashed lines according to BS EN ISO 128 standards.
6. Label views and add the first angle symbol: Place the symbol near the title block for clear identification.

Importance of first angle projection in Kenyan workplaces

1. Standardized communication: Ensures consistent interpretation of drawings across teams in hospitals and manufacturing.
2. Ease of visualization: Provides a clear spatial relationship between views, aiding fabrication in county government workshops.
3. Regulatory compliance: Aligns with international standards adopted by Kenyan TVET institutions.
4. Cost efficiency: Reduces errors in production by clarifying component geometry.
5. Training relevance: Prepares students for local industries that use first angle projection as a norm.

Differences between first angle and third angle projection

1. View placement: In first angle, the top view is below the front; in third angle, it is above.
2. Object location: First angle places the object in the first quadrant; third angle places it in the third quadrant.
3. Symbol difference: Each method has a distinct symbol for easy identification.
4. Regional preference: First angle is prevalent in Europe and parts of Africa; third angle is dominant in the USA.
5. Interpretation: Misreading the projection method can cause fabrication errors in sectors like agriculture machinery manufacturing.

3.1.2 Third angle projection

Third angle projection is another principal orthographic projection technique, widely used in Kenya’s educational institutions and some industrial sectors such as banking equipment design and ICT hardware layout.

Definition and principles of third angle projection

1. Object placement: The projection planes are between the observer and the object.
2. View arrangement: The top view is placed above the front view, and the right side view is placed on the right side of the front view.
3. Projection planes: Similar three perpendicular planes are used as in first angle but arranged differently.
4. View alignment: Views are arranged in a way that resembles unfolding the object’s surfaces outward.
5. Symbol: The third angle symbol is a truncated cone with the small end facing right.

Procedure for constructing third angle projection

1. Determine the front view: Select the most descriptive face of the object.
2. Project the top view: Draw the horizontal plane above the front view and project points vertically upward.
3. Project the right side view: Draw the profile plane to the right of the front view and project points horizontally to the right.
4. Draw projection lines: Use orthogonal lines perpendicular to each plane.
5. Show hidden features: Use dashed lines for hidden edges per ISO standards.
6. Include the third angle symbol: Place it prominently in the drawing title block area.

Advantages of third angle projection in Kenyan industries

1. Global compatibility: Useful for Kenyan businesses exporting products or collaborating internationally.
2. Intuitive layout: Aligns with natural viewing perspectives, easing interpretation by non-technical staff.
3. Educational use: Preferred in many Kenyan TVET colleges for teaching technical drawing basics.
4. Versatility: Applies well to varied sectors such as hotel kitchen equipment design.
5. Error reduction: Clear view arrangement reduces miscommunication in component fabrication.

Comparison of first and third angle projections in practice

Chapter Summary

This chapter focused on producing orthographic drawings of components, starting with a detailed explanation of orthographic projections, including both first angle and third angle projection methods. It emphasized the importance of selecting the appropriate projection technique based on industry standards to accurately represent three-dimensional objects in two dimensions. Dimensioning principles were covered to ensure precise communication of size and location on drawings, following standard conventions. The chapter also explored sectional views as a critical tool for revealing internal features of components that are not visible in standard orthographic projections. Free hand sketching techniques were introduced, highlighting the ability to quickly convey ideas through geometric forms and the use of essential drawing tools and equipment. Attention was given to sketching mechanical components with clarity and accuracy as a foundation for more detailed technical drawings. Overall, the chapter integrated theory with practical drawing procedures to build competence in producing clear, standardized orthographic drawings.