Producing accurate plane geometry drawings is fundamental for Building Technology professionals in Kenya. These drawings form the basis for designing, planning, and executing construction projects, ensuring all stakeholders have a clear understanding of spatial relationships and dimensions. Mastery of line types and conventions according to recognized standards allows for effective communication and compliance with regulatory requirements, reducing errors and enhancing project quality.

2.1 Types of lines used in drawings

In Building Technology, different types of lines convey specific information on technical drawings. Understanding these line types is essential for clear representation of objects, boundaries, and features in plans, sections, and elevations. Kenyan professionals rely on British Standards (BS 8888) and ISO conventions adapted locally to ensure drawings are universally interpretable and meet industry standards.

2.1.1 Purpose of different line types in plane geometry drawings

Different line types serve distinct purposes that help differentiate elements on a drawing. Their correct use avoids ambiguity and improves readability, which is critical on construction sites and in project documentation.

• Object Lines represent visible edges of objects. They are thick continuous lines that outline the shape and form of building components.
• Hidden Lines indicate edges not visible in the current view. These are medium thickness dashed lines that help visualize internal or obscured features.
• Centre Lines mark axes of symmetry or the center of circles and arcs. They are thin lines alternating long and short dashes, helping to locate geometric centers.
• Dimension Lines show distances and measurements. These thin continuous lines have arrowheads at ends and are placed between extension lines.

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

• Extension Lines extend from the object to dimension lines, indicating the exact points being measured. They are thin and do not touch the object lines.

A technical drawing illustrating the use of extension lines and dimens (Source: 59d646f026634d9a)

• Cutting Plane Lines indicate where a section is taken. These are thick dashed lines with arrows showing the direction of the section view.

2.1.2 Characteristics and standards for line types in building drawings

Kenyan Building Technology professionals adhere to BS 8888 and ISO 128 standards for line types, ensuring consistency and clarity.

• Line Weight varies according to line function. Object lines are thick (0.7 to 1.0 mm), hidden lines medium (0.35 to 0.5 mm), and center lines thin (0.18 to 0.35 mm).
• Line Style includes continuous, dashed, chain, and dotted patterns. Each pattern corresponds to specific features such as visible edges or hidden details.
• Colour in manual drawings is rarely used; however, CAD drawings may employ colours for clarity, but final prints must conform to monochrome standards.
• Scale Considerations affect line thickness; smaller scales require finer lines to avoid clutter, while larger scales permit bolder lines.
• Title Block and Legend must clearly define line types used in the drawing to assist readers unfamiliar with the specific conventions.

2.1.3 Drawing tools and equipment for producing line types

• Use mechanical pencils for drafting fine lines, adjusting lead hardness for line weight.
• Technical pens are preferred for final drawings, ensuring uniform line thickness.
• Rulers and French curves facilitate precise straight and curved lines, essential for clean geometry.
• The eraser shield protects adjacent lines when making corrections, preserving line integrity.

2.1.4 Procedure for drawing standard line types in plane geometry

1. Select appropriate drawing tool based on line type and desired thickness.
2. Use ruler or template to guide straight or curved lines ensuring accuracy.
3. Draw object lines first as thick continuous lines outlining visible edges.
4. Add hidden lines using dashed patterns to show obscured features.
5. Insert centre lines as alternating long and short dashes at symmetry axes or circle centers.
6. Draw dimension and extension lines thinly, placing arrowheads and measurement figures clearly.
7. Review line weights and styles against BS 8888 to confirm conformity.
8. Label line types in the drawing legend or title block for clarity.
9. Use eraser shield to correct any mistakes without damaging adjacent lines.
10. Final inspection to ensure all lines are clear, continuous where required, and correctly spaced.

Chapter Summary

This chapter covered the essential types of lines used in technical drawings, highlighting their specific roles and standards. It then detailed the step-by-step construction of various geometric forms including circles, triangles, rectangles, parallelograms, polygons, pyramids, conic sections, prisms, and loci, emphasizing precision and adherence to drawing conventions. The chapter also explained the construction of different types of angles, providing clear methods to accurately measure and bisect these angles in drawings. Attention was given to the practical skills of freehand sketching geometric forms, supported by the proper use of drawing tools and equipment. Throughout, the importance of following established standards to ensure clarity and accuracy in plane geometry drawings was reinforced. This foundation enables students to confidently produce and interpret technical drawings essential for various engineering and design applications.