Producing accurate plane geometry drawings is fundamental across all professional fields in Kenya, from designing layouts in hospitals to planning spaces in retail businesses. Understanding the types of lines used in technical drawings ensures clear communication of design intent, specifications, and modifications. This chapter focuses on the standard line types employed in technical drawings, their characteristics, and their proper application according to international and Kenyan standards.

2.1 Types of lines in drawings

In professional settings such as county government offices or universities, technical drawings must follow precise conventions to avoid misinterpretation. Lines are the primary means of conveying information about shapes, dimensions, and features in drawings. Different types of lines signify distinct elements such as visible edges, hidden details, or cutting planes. Mastery of these line types is essential for producing drawings that meet BS EN ISO 128 and Kenya Bureau of Standards (KEBS) requirements.

2.1.1 Boarder lines

Boarder lines, also known as border lines, define the outer edges of the drawing sheet and the drawing area, framing the entire technical document. They ensure the drawing is neatly contained and provide a clear boundary for all included details.

Purpose of boarder lines

• Define drawing limits: Boarder lines outline the maximum area where drawing content can appear, preventing overflow.
• Enhance presentation: They provide a professional, clean appearance to the drawing sheet, improving readability.
• Facilitate sheet handling: Boarders help in aligning and stacking multiple sheets in filing systems used in offices such as banks and SACCOs.
• Support title block placement: The border creates a designated space for the title block and revision notes, essential in county government office documentation.
• Standardize sheet sizes: Boarders maintain consistency across different drawings, aiding in compliance with ISO and Kenyan standards.

Characteristics of boarder lines

• Line thickness: Boarder lines are drawn using a thick continuous line, typically 0.5 mm or more, to stand out clearly.
• Continuous line type: They are unbroken and solid, ensuring no ambiguity in the drawing boundary.
• Position: Located at a fixed distance from the edge of the drawing sheet, usually 10 mm inside to prevent damage.
• Shape: Usually rectangular, matching the shape of the drawing sheet.
• Uniformity: The thickness and position remain consistent across all sheets of a project to maintain standardization.

Drawing boarder lines: step-by-step procedure

1. Select the appropriate drawing sheet size according to the project requirements.
2. Measure 10 mm from each edge of the sheet to mark the border line position.
3. Using a 0.5 mm technical drawing pen or pencil, draw a continuous rectangle connecting the four marks.
4. Check line thickness with a ruler or template to ensure uniformity.
5. Avoid any breaks or gaps in the line during drawing.
6. Allow ink to dry or fix the pencil lines to prevent smudging during handling.

2.1.2 Faint continuous lines

Faint continuous lines, sometimes called construction lines, are lightly drawn lines used as guides during drawing construction. They help in establishing shapes, angles, and proportions without dominating the final drawing.

Role of faint continuous lines

• Guide drawing layout: They assist in accurately positioning elements before finalizing.
• Maintain proportions: Aid in measuring and scaling complex geometries.
• Support shape construction: Used to build auxiliary lines, such as bisectors and tangents.
• Facilitate corrections: Easily erased or overridden without affecting the final drawing.
• Provide reference points: Mark centers, intersections, or alignments subtly.

Properties of faint continuous lines

• Line thickness: Typically 0.2 mm or less, thinner than border or visible lines.
• Appearance: Solid and unbroken but light enough to be distinguishable from main outlines.
• Erasability: Drawn lightly to allow easy removal or modification.
• Consistency: Uniform thinness throughout the drawing.
• Use of pencil: Commonly drawn with hard pencils (H or 2H) for precision and lightness.

Best practices when using faint continuous lines

1. Begin all sketches with faint lines to outline basic shapes.
2. Avoid excessive pressure to keep lines light and erasable.
3. Use a ruler or drafting tools to maintain straightness and accuracy.
4. Erase faint lines only after final lines are confirmed and darkened.
5. Maintain consistency in line thickness throughout the drawing.
6. Avoid overusing faint lines to prevent clutter and confusion.

2.1.3 Broken lines

Broken lines, also known as hidden lines, represent edges or surfaces not visible from the current viewing angle. These lines communicate concealed features in objects or layouts, such as piping behind walls in a hospital plan.

Purpose of broken lines

• Indicate hidden features: Show parts obscured by other components.
• Clarify complex assemblies: Help visualize internal structures without multiple views.
• Assist in fabrication: Provide essential information to manufacturing or construction teams.
• Support inspection: Highlight areas for quality checks or maintenance.
• Avoid ambiguity: Differentiate between visible and non-visible edges clearly.

Characteristics of broken lines

• Line type: Short, evenly spaced dashes typically 3 mm long with 2 mm gaps.
• Line thickness: Medium thickness (0.3 mm to 0.5 mm), thinner than border lines but thicker than faint lines.
• Continuity: Broken but regular pattern to maintain clarity.
• Placement: Drawn precisely where hidden edges exist in the projection.
• Standard compliance: Follow BS EN ISO 128 and KEBS guidelines for dash length and spacing.

Drawing broken lines procedure

1. Identify hidden edges or features not visible in the current view.
2. Use a technical pen or pencil with 0.3 mm thickness for broken lines.
3. Mark dashes approximately 3 mm in length separated by 2 mm gaps along the hidden edge path.
4. Maintain equal spacing and consistent dash length for neatness.
5. Avoid overlapping broken lines with visible lines.
6. Review the drawing to ensure all hidden features are correctly represented.

2.1.4 Chain lines

Chain lines are used to indicate special features such as center lines of symmetry, paths of motion, or important limits like cutting planes. They consist of alternating long and short dashes.

Functions of chain lines

• Mark cutting planes: Define where an object is sectioned for detailed views.
• Indicate symmetry: Show axes or planes of symmetry in designs.
• Highlight limits: Denote boundaries of areas under inspection or modification.
• Depict motion paths: Visualize movement or rotation axes.
• Provide reference: Assist in aligning components during assembly.

Chain line features

• Pattern: Alternating long dashes (6 mm) and short dashes (2 mm).
• Thickness: Medium, similar to broken lines (0.3 mm to 0.5 mm).
• Continuity: Continuous with no breaks in pattern.
• Annotations: Often accompanied by arrows or labels for clarity.
• Standardized: Compliant with ISO and KEBS standards for technical drawings.

Steps to draw chain lines

1. Determine the feature requiring a chain line, such as a cutting plane.
2. Use a 0.3 mm pen or pencil for line thickness.
3. Draw a long dash approximately 6 mm in length.
4. Follow with a short dash of 2 mm.
5. Repeat the alternating pattern along the required length.
6. Add arrows or labels to indicate direction or feature name where necessary.

2.1.5 Centre lines

Centre lines identify the geometric centers of circles, arcs, or symmetrical parts. They help in dimensioning and locating features accurately in technical drawings.

Importance of centre lines

• Locate features: Pinpoint centers of holes, circles, and arcs.
• Assist dimensioning: Provide reference for radial or symmetrical measurements.
• Support assembly: Ensure parts align correctly during construction.
• Highlight symmetry: Mark central axes in mechanical or architectural plans.
• Aid machining: Guide tool paths and fixture placements.

Characteristics of centre lines

• Line style: Long and short dashes alternating, similar to chain lines but thinner.
• Thickness: Thin, approximately 0.2 mm.
• Length: Extend slightly beyond the feature boundaries for clarity.
• Continuity: Continuous alternating dash pattern.
• Standard adherence: Follow ISO 128 and KEBS for dash length and spacing.

Procedure for drawing centre lines

1. Identify the center point of the circle, arc, or symmetrical feature.
2. Draw a thin line with alternating long (6 mm) and short (3 mm) dashes through the center.
3. Extend the line beyond the feature’s edges by at least 5 mm.
4. Cross two centre lines perpendicular to each other for circular features to mark centers.
5. Use a 0.2 mm technical pen for clarity.
6. Ensure lines are straight using a ruler or drafting tools.

2.1.6 Cutting lines

Cutting lines indicate where an object is sliced to reveal internal features in sectional views. They are crucial in detailed technical drawings for hospitals, retail outlets, or educational facilities to show hidden internal arrangements.

Purpose and significance of cutting lines

• Define section planes: Show exact location of the cut.
• Clarify internal details: Reveal features not visible externally.
• Guide fabrication: Provide instructions for assembly or construction.
• Improve understanding: Enhance visualization of complex structures.
• Facilitate quality assurance: Assist inspectors in verifying internal configurations.

Features of cutting lines

• Line style: Thick chain line with alternating long and short dashes.
• Thickness: Similar to border lines, approximately 0.5 mm.
• Arrows: Include arrows at ends to indicate viewing direction.
• Labels: Often marked with letters (A-A, B-B) to reference sectional views.
• Standard compliance: Must conform to BS EN ISO 128 and KEBS standards.

Drawing cutting lines step-by-step

1. Identify the plane along which the section is to be taken.
2. Draw a thick chain line along this plane using 0.5 mm thickness.
3. Mark arrows at both ends pointing in the direction of the view.
4. Label the cutting line with appropriate letters to correspond with the sectional drawing.
5. Ensure the cutting line extends beyond the object edges for visibility.
6. Verify line style and labels conform to standard drawing conventions.

Chapter Summary

This chapter covered the essential types of lines used in engineering drawings, including border lines, faint continuous lines, broken lines, chain lines, centre lines, and cutting lines, each serving specific purposes in technical representation. It detailed the procedures for constructing various angles such as acute, right, reflex, obtuse, and straight angles, emphasizing accuracy in geometric constructions. The bisection of these angles was explained step-by-step to aid precise division, followed by methods for measuring the same angles using appropriate drawing instruments. The construction of plane geometric forms was explored extensively, focusing on triangles, quadrilaterals, polygons, and circles with tangents, highlighting the importance of correct shape formation. Various scale constructions were introduced, including plane scales, diagonal scales, and reducing and enlargement scales, to support accurate representation of dimensions. The chapter reinforced these concepts through repeated emphasis on geometric forms and scale construction, ensuring mastery of fundamental drawing skills crucial for producing solid geometry drawings. Through these topics, students developed a comprehensive understanding of plane geometry drawing techniques aligned with engineering drawing standards.