Technical drawing is a fundamental skill across many Kenyan professional fields, from healthcare facility management to agricultural cooperative planning and retail business layout design. Accurate plane geometry drawings communicate ideas clearly and ensure precision in projects. This chapter focuses on essential drawing components: the types of lines used to convey different information and the freehand printing of letters to ensure legibility and professionalism in technical documents.

2.1 Types of Lines in Drawings

2.1.1 Classification of Lines According to Standards

Technical drawing lines follow conventions specified in BS 8888 and ISO 128 standards, which Kenyan TVET students must master for professional competence. The main line types include continuous, dashed, chain, and phantom lines.

• Continuous Thick Line: Used for visible edges and outlines of objects. This line is bold to emphasize the object's shape.
• Continuous Thin Line: Represents dimension lines, projection lines, hatching, and short leader lines. It is lighter to avoid overpowering the main outline.
• Dashed Line: Indicates hidden edges or features not visible in the current view. It helps visualize internal details without sectioning.
• Chain Line (Long dash followed by a short dash): Used to indicate center lines, lines of symmetry, or paths of motion.
• Phantom Line (Long dash followed by two short dashes): Represents alternate positions of parts or adjacent components.

These line types must be used consistently in drawings produced for county referral hospitals, retail store layouts, or SACCO office plans to maintain clarity.

2.1.2 Line Thickness and Scale Considerations

Line thickness varies to prioritize information in drawings. Kenyan professionals designing plans for hotels or NEMA environmental impact diagrams must select appropriate line weights.

• Thick Lines: Typically 0.7 mm to 1.0 mm, used for visible outlines and cutting planes.
• Medium Lines: Around 0.5 mm, for dimension lines and hatching.
• Thin Lines: Between 0.25 mm and 0.35 mm, for projection lines and short leader lines.

Line thickness should scale proportionally with the drawing scale to ensure visibility without cluttering. For example, a site plan at 1:500 may use thicker lines than a detailed component drawing at 1:20.

2.1.3 Line Types and Their Application in Drawings

Different drawings require specific line types to communicate effectively. For instance, in agricultural cooperative layouts or bank branch floor plans:

• Visible Edges: Drawn with thick continuous lines to define the object's shape.
• Hidden Details: Dashed lines reveal internal features such as plumbing or wiring behind walls.
• Center Lines: Chain lines mark axes of symmetry or rotation in machinery layouts or structural drawings.
• Dimension Lines: Thin continuous lines with arrowheads indicate measurements clearly.

Engineering drawing with dimension lines shown (Source: Wikimedia Commons)

• Cutting Planes: Thick chain lines highlight where a section has been taken.

Selecting the correct line type ensures that technicians, architects, or facility managers understand the drawing without ambiguity.

2.1.4 Compliance with Kenyan and International Standards

Kenyan professionals must align drawing practices with BS 8888 and ISO 128 to meet industry expectations and regulatory requirements. County government offices and university technical departments often audit drawings for standard compliance.

• Line Types: Must follow prescribed patterns and thickness.
• Scale Indication: Drawings should clearly state the scale used.
• Title Blocks: Include essential information such as drafter name, date-scale, and drawing number.
• Symbols and Notations: Use standard symbols for features like doors, windows, or electrical outlets.
• Paper Size and Orientation: Drawings should conform to ISO A-series sizes with appropriate orientation for the content.

Adhering to these standards ensures drawings are professional, universally understandable, and legally acceptable.

Chapter Summary

This chapter provided a comprehensive overview of producing plane geometry drawings, beginning with the identification and application of various types of lines used in technical drawings. It emphasized the importance of mastering freehand printing of letters to ensure clarity and professionalism in annotations. The role of borderlines and title blocks was explained as essential elements for standardizing drawing presentation. Detailed procedures for constructing and measuring different angles were covered, alongside techniques for bisecting angles and lines accurately. The chapter then explored the construction of fundamental geometric figures such as circles, triangles, rectangles, parallelograms, polygons, pyramids, conic sections, and prisms, highlighting their individual drawing methods. Pattern development was introduced as a key step in translating three-dimensional objects into flat layouts. The discussion on tangents distinguished between exterior and interior tangents to circles, illustrating their construction principles. Finally, the chapter concluded with the standard drawing conventions that govern line types, scales, symbols, and title block formats to ensure consistency and adherence to recognized technical standards.