Technical drawing is an essential skill across all professional sectors in Kenya, enabling clear communication of ideas, designs, and plans. Whether in healthcare facilities, county government offices, or retail businesses, accurate drawings ensure that concepts are understood and executed correctly. This chapter focuses on producing plane geometry drawings by mastering the types of lines used, which form the foundation of technical communication in any workplace.

2.1 Types of lines in drawings

In technical drawings, lines are fundamental elements that convey specific information about shapes, boundaries, and features. Understanding the standardized types of lines and their correct application is crucial for producing clear, precise, and professional drawings. Kenyan workplaces such as universities, SACCOs, and hospitals rely on these conventions to avoid misinterpretation and ensure consistency.

2.1.1 Boarder lines

Boarder lines define the limits of the drawing sheet and separate the drawing area from the title block and notes. They provide a neat, professional frame that helps organize the drawing and ensures it fits standard sizes used in Kenyan institutions such as county referral hospitals and TVET colleges.

Purpose of boarder lines

• Define Drawing Boundaries: Boarder lines clearly mark the edges of the drawing sheet, ensuring that all drawing elements fit within a standardized space.
• Enhance Presentation: They provide a clean frame that improves the visual appeal and readability of the drawing.
• Separate Title Block: Boarder lines demarcate the main drawing area from the title block, facilitating easy identification of drawing information.
• Standardization Compliance: Using boarder lines ensures adherence to Kenya Bureau of Standards (KEBS) and ISO drawing sheet size requirements.
• Protection of Drawing Content: They prevent important drawing details from being cut off during printing or copying.

Characteristics of boarder lines

• Thickness: Boarder lines are drawn thick and continuous, usually 0.7 mm or more, to stand out clearly.
• Positioning: They run parallel to the edges of the paper, leaving a uniform margin (typically 10 mm) inside the sheet edges.
• Continuity: The lines are unbroken to provide a solid rectangular frame.
• Standard Dimensions: Boarder lines conform to standard paper sizes such as A4, A3, or A2 as per KEBS and ISO 128.
• Contrast: The thickness and darkness of boarder lines distinguish them from other thinner construction lines.

Drawing boarder lines: step-by-step procedure

1. Select the appropriate paper size according to the drawing requirements, for example, A3 for county government office plans.
2. Measure 10 mm from each edge of the paper to create a uniform margin.
3. Mark four points at the 10 mm distance on all sides, ensuring they form a rectangle.
4. Using a ruler and pencil, draw a continuous line connecting the marked points, forming the boarder.
5. Trace over the pencil line with a 0.7 mm technical pen or darker pencil to enhance visibility.
6. Verify the boarder dimensions to confirm uniformity and adherence to standards.

Importance of boarder lines in professional drawings

• Ensures Consistency: Helps maintain uniformity across drawings produced in organizations like banks and retail businesses.
• Facilitates Filing and Storage: Standardized boarders allow easy filing and referencing in offices such as county government departments.
• Improves Legibility: Clear boundaries make it easier for viewers to focus on the drawing content without distraction.
• Supports Reproduction: Boarders prevent loss of drawing content during photocopying or scanning in institutions like universities.
• Legal Compliance: Many regulatory bodies require drawings with proper boarders for approval, such as NEMA for environmental plans.

2.1.2 Faint continuous lines

Faint continuous lines are light, thin lines used mainly for construction, guidelines, and dimensioning in technical drawings. Kenyan professionals in sectors such as agriculture and cooperatives use these lines to draft initial sketches and add measurement details without overpowering the main drawing features.

Purpose of faint continuous lines

• Guide Construction: They serve as reference lines to construct shapes and angles accurately.
• Indicate Dimensions: Used to draw extension and dimension lines that show measurements.

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

• Assist in Layout: Help in positioning elements on the drawing sheet before finalizing the design.
• Separate Details: Provide a visual distinction between temporary guidelines and permanent outlines.
• Enable Modifications: Make it easier to erase or adjust parts of the drawing during the design process.

Characteristics of faint continuous lines

• Thickness: Thin lines typically between 0.18 mm and 0.25 mm.
• Lightness: Drawn lightly to avoid confusion with main outlines.
• Continuity: Lines are unbroken but subtle.
• Smoothness: Should be straight and steady to aid accuracy.
• Usage with Tools: Often drawn using a hard pencil (e.g., 2H) or fine technical pen.

Drawing faint continuous lines: procedure

1. Select a hard pencil (2H) or a fine technical pen for light line work.
2. Using a ruler or set square, lightly sketch the required guideline or dimension line.
3. Ensure the line is straight and continuous without breaks.
4. Draw extension lines from the object edges outward, leaving space for dimension figures.
5. Add dimension lines parallel to the extension lines, placing arrowheads or ticks at ends.
6. Write dimension figures clearly above or beside the dimension lines, ensuring legibility.

Importance of faint continuous lines in technical drawings

• Clarity in Measurements: They keep dimensions separate from object outlines, preventing confusion.
• Facilitate Accurate Drafting: Provide necessary guides for constructing precise drawings in schools and TVET colleges.
• Allow Easy Corrections: Lightness enables erasing without damaging the main drawing.
• Enhance Professionalism: Clean, faint lines contribute to neat, well-organized drawings.
• Support Communication: Help stakeholders like hotel managers understand sizes and placements without clutter.

2.1.3 Broken lines

Broken lines are dashed lines used to represent hidden edges and features not visible in the current view of a drawing. Organizations like retail businesses and banks use broken lines to communicate details such as concealed structural elements or internal components.

Purpose of broken lines

• Indicate Hidden Features: Show edges or details obscured behind visible surfaces.
• Represent Internal Structures: Illustrate components inside objects, such as wiring in a hotel electrical plan.
• Clarify Overlapping Parts: Help distinguish between visible and invisible parts in complex assemblies.
• Assist in Planning: Provide information needed for maintenance or installation without extra drawings.
• Standardize Communication: Maintain uniformity in representing hidden details across various sectors.

Characteristics of broken lines

• Pattern: Consist of short dashes, usually around 3 mm long, separated by equal spaces.
• Thickness: Medium thickness, typically 0.35 mm to 0.5 mm.
• Continuity: Dashed but evenly spaced.
• Visibility: Dark enough to be clear but not overpower main outlines.
• Placement: Drawn where hidden edges exist behind visible surfaces.

Drawing broken lines: procedure

1. Identify hidden edges or features in the object or plan.
2. Select a medium thickness technical pen or pencil for drawing.
3. Using a ruler, mark the start and end points of the hidden feature line.
4. Draw short dashes approximately 3 mm long, leaving equal gaps between each dash.
5. Maintain consistent dash length and spacing throughout the line.
6. Ensure the broken line aligns with the hidden edge’s position relative to visible features.

Importance of broken lines in professional drawings

• Reveal Concealed Details: Enable engineers and architects in county government offices to understand full structural layouts.
• Avoid Drawing Clutter: Show hidden features without adding separate sectional views.
• Assist Maintenance Teams: Provide information for repair work in hospitals or retail outlets.
• Standardize Drawings: Ensure consistent interpretation across multidisciplinary teams.
• Improve Accuracy: Help avoid construction errors by clearly indicating unseen components.

2.1.4 Chain lines

Chain lines consist of alternating long and short dashes and are used to indicate centre lines, cutting planes, or special features in drawings. Kenyan professionals in sectors such as NEMA and cooperative societies rely on chain lines to differentiate critical elements like section cuts or boundaries.

Purpose of chain lines

• Mark Centre Lines: Identify axes of symmetry or rotation.
• Indicate Cutting Planes: Show where an object is cut for sectional views.
• Highlight Special Features: Denote important boundaries or limits.
• Distinguish from Other Lines: Separate chain lines from continuous or broken lines to avoid confusion.
• Support Detailed Analysis: Assist in understanding complex drawings in environmental reports or cooperative audits.

Characteristics of chain lines

• Pattern: Alternating long (about 6 mm) and short dashes (about 3 mm).
• Thickness: Medium thickness, similar to broken lines (0.35 mm to 0.5 mm).
• Continuity: Continuous alternating pattern without breaks.
• Visibility: Dark enough to stand out but not dominate the drawing.
• Placement: Positioned precisely according to the feature being marked.

Drawing chain lines: procedure

1. Determine the feature to be marked (centre line, cutting plane, etc.).
2. Select appropriate drawing tools such as a 0.5 mm technical pen.
3. Using a ruler, draw a long dash approximately 6 mm.
4. Follow with a short dash about 3 mm.
5. Repeat the alternating pattern continuously along the required length.
6. Ensure the line is straight and accurately positioned relative to the drawing elements.

Importance of chain lines in technical drawings

• Clarify Drawing Intent: Clearly shows where sections or symmetry exist in designs for banks or hotels.
• Aid in Interpretation: Helps users distinguish cutting planes from other line types.
• Enhance Accuracy: Ensures correct placement of sectional views in environmental impact drawings by NEMA.
• Improve Visual Hierarchy: Differentiates special features without cluttering the drawing.
• Facilitate Collaboration: Enables multidisciplinary teams to understand complex drawings easily.

2.1.5 Centre lines

Centre lines are thin lines made up of alternating long and short dashes, used to indicate the geometric centre of circles, arcs, or symmetrical objects. They are vital in organizations such as universities and SACCOs when producing accurate technical drawings of equipment or facilities.

Purpose of centre lines

• Identify Geometric Centres: Mark the centre point or axis of circles and arcs.
• Define Symmetry: Show symmetry axes in parts or assemblies.
• Aid in Measurement: Provide reference points for dimensioning and construction.
• Support Assembly Instructions: Help in locating holes, shafts, or features during manufacturing.
• Standardize Drawing Language: Ensure uniform understanding of centre positions across professional sectors.

Characteristics of centre lines

• Pattern: Alternating long and short dashes; long dashes about 6 mm, short about 3 mm.
• Thickness: Thin lines, usually 0.18 mm to 0.25 mm.
• Continuity: Continuous alternating pattern without breaks.
• Length: Lines extend beyond the feature edges to provide clear reference.
• Contrast: Light enough not to overpower object outlines but visible for reference.

Drawing centre lines: procedure

1. Identify the centre of the circle or symmetrical object using compasses or measurement.
2. Place the ruler or straight edge through the centre point for straight centre lines.
3. Draw a long dash approximately 6 mm through the centre.
4. Follow with a short dash about 3 mm.
5. Continue the alternating pattern extending beyond the object edges.
6. Repeat perpendicular centre lines if necessary to indicate multiple axes of symmetry.

Importance of centre lines in technical drawings

• Ensure Precision: Crucial for locating holes or features in equipment drawings for TVET college workshops.
• Facilitate Layout: Assist in planning symmetrical structures in county government office layouts.
• Enhance Clarity: Help avoid ambiguity in complex shapes by marking centres clearly.
• Support Manufacturing: Guide machining and assembly processes in cooperative business equipment.
• Maintain Standardization: Compliance with ISO and KEBS drawing conventions ensures drawings are understood universally.

2.1.6 Cutting lines

Cutting lines indicate the location where an object is cut to produce a sectional view. These lines are essential in revealing internal features and details, commonly used in environmental impact plans or facility layouts for organizations such as NEMA and county referral hospitals.

Purpose of cutting lines

• Mark Section Locations: Show exactly where the object is sliced for sectional drawings.
• Reveal Internal Details: Allow visualization of hidden features within complex objects.
• Assist in Design Understanding: Provide clearer insight into construction or assembly.
• Support Quality Control: Enable inspection of internal parts in hospital equipment maintenance.
• Standardize Documentation: Ensure consistent presentation of sectional views across sectors.

Characteristics of cutting lines

• Pattern: Thick chain lines with alternating long and short dashes, often with arrowheads indicating the viewing direction.
• Thickness: Heavier than centre lines, typically 0.5 mm to 0.7 mm.
• Arrowheads: Placed at ends pointing towards the section view.
• Labeling: Cutting lines are often labeled with letters (e.g., A-A) to identify the section.
• Positioning: Drawn precisely where the cut occurs, aligned with the object features.

Drawing cutting lines: procedure

1. Determine the section plane location on the object or plan.
2. Use a technical pen of thickness 0.5 mm or more for drawing.
3. Draw a continuous chain line with long and short dashes along the section plane.
4. Add arrowheads at both ends, pointing in the direction of the view.
5. Label the cutting line with capital letters to identify the section.
6. Ensure the cutting line is clearly distinguishable from other lines on the drawing.

Importance of cutting lines in technical drawings

• Facilitate Detailed Visualization: Help engineers and planners in county referral hospitals understand internal layouts.
• Improve Communication: Provide clear instructions for construction or assembly teams.
• Enhance Accuracy: Reduce errors by clearly indicating where to view internal sections.
• Support Documentation: Essential for compliance with KEBS and ISO standards in technical reports.
• Aid in Training: Assist TVET students and trainees in comprehending complex designs.

Chapter Summary

This chapter focused on the essential elements of producing plane geometry drawings, beginning with the identification and purpose of different types of lines such as border lines, faint continuous lines, broken lines, chain lines, centre lines, and cutting lines. It then covered the step-by-step construction of various angles, including acute, right, reflex, obtuse, and straight angles, providing the foundation for accurate geometric shapes. The process of bisecting these angles was explored in detail to ensure precise division and symmetry. Measurement techniques for each angle type were also discussed to enable accurate verification during drawing. The chapter further addressed the construction of fundamental plane geometric forms such as triangles, quadrilaterals, polygons, and circles with tangents, emphasizing correct procedures and standards. Finally, it explained how to construct different types of scales including plane scales, diagonal scales, and scales for reducing or enlarging drawings, which are critical for maintaining proportional accuracy in technical drawings. Together, these topics equip learners with comprehensive skills to produce clear, precise, and standardized plane geometry drawings.