Technical drawing is an essential skill for Automotive Engineering Technology professionals in Kenya. Accurate plane geometry drawings form the foundation for designing, assembling, and repairing vehicle components. Understanding the correct use of line types ensures clarity and precision in communication between engineers, technicians, and manufacturers. This chapter focuses on the types of lines used in technical drawings and their specific applications in automotive engineering.

2.1 Types of Lines in Drawings

In automotive technical drawings, various line types convey different meanings and instructions. Using the correct line type according to British Standards (BS 8888) and ISO conventions ensures universal understanding and reduces errors in manufacturing and maintenance. This section covers the primary line types used in automotive engineering drawings, highlighting their characteristics and specific uses.

2.1.1 Boarder Lines

Boarder lines define the outer edges of the drawing sheet and separate the drawing area from title blocks and notes, ensuring neatness and organization.

Purpose of Boarder Lines

• Frame the drawing sheet: Boarder lines create a clear boundary around the drawing space to confine all graphic content.
• Separate drawing from annotations: They distinguish the drawing area from margin notes and title blocks.
• Provide uniformity: Boarder lines standardize the layout of technical drawings across automotive workshops.
• Facilitate scaling: The defined space aids in the correct application of drawing scales.
• Assist in reproduction: Clear borders prevent cutting off important details during photocopying or scanning.

Characteristics of Boarder Lines

• Continuous thick line: Boarder lines are drawn with a thick, continuous stroke to stand out.
• Consistent width: Typically 0.5 mm or as specified by BS 8888 for clarity.
• Straight and closed: They form a rectangular frame enclosing the drawing area.
• Located at sheet edges: Positioned close to the paper edges but leaving space for binding or handling.
• Uniform spacing: The border maintains equal distance from the sheet edges on all sides.

Drawing Procedure for Boarder Lines

1. Select the drawing sheet and mark the outermost edges.
2. Measure and mark the boarder margin, usually 10-20 mm from each edge.
3. Use a ruler and a 0.5 mm technical pen or pencil to draw straight continuous lines connecting the margin marks.
4. Ensure the lines form a closed rectangle without gaps.
5. Double-check measurements for uniformity on all sides.
6. Label the title block and notes outside the boarder lines.

Application in Automotive Drawings

• Used in all vehicle component layout sheets for clear demarcation.
• Essential in assembly drawings to separate detailed parts from notes.
• Helps technicians focus on the drawing area without distraction.
• Enhances presentation quality for client submissions.
• Ensures compatibility with digital scanning and printing standards.

2.1.2 Faint Continuous Lines

Faint continuous lines, also called construction or guide lines, provide reference without overpowering the main drawing features.

Meaning and Purpose

• Aid in construction: They guide the placement of primary lines and shapes.
• Temporary references: Used during initial drawing stages and removed or faded in final versions.
• Help in alignment: Assist in maintaining symmetry and proportion.
• Do not represent physical features: They are not part of the actual object.
• Support dimensioning: Provide baseline for placing dimensions and annotations.

Characteristics and Standards

• Thin continuous line: Typically 0.13 mm line width.
• Light pressure or faint ink: To ensure they are distinguishable but not dominant.
• Straight or curved: Depending on the geometry being constructed.
• Non-permanent: Often drawn in pencil or light ink.
• Follow BS 8888 guidelines: For consistency in technical documentation.

Drawing Faint Continuous Lines in Automotive Context

1. Identify the main shape or feature to be constructed.
2. Lightly mark construction points or intersections.
3. Draw faint continuous lines connecting these points with a 0.13 mm line.
4. Check alignment and adjust as necessary.
5. Use these lines to position circles, arcs, or other geometric features.
6. Erase or reduce visibility after completing the main drawing lines.

Importance in Vehicle Part Design

• Ensures precision in forming complex curves like camshaft lobes.
• Guides layout of symmetrical parts such as brake discs.
• Facilitates dimensioning of engine block features.
• Assists in marking drilling points on chassis components.
• Enables clear layering of drawing elements for clarity.

2.1.3 Broken Lines

Broken lines represent hidden edges or features not visible in the current view of the object.

Definition and Use

• Indicate hidden details: Show internal or obscured parts.
• Assist in understanding complex shapes: Reveal holes, slots, or recesses.
• Clarify assembly relationships: Highlight parts behind others.

• Used in orthographic projections: Common in front, top, and side views.

• Avoid confusion with other line types: Must be distinct and standardized.

Characteristics and Standards

• Short dashes with equal spacing: Typically 3 mm dash, 1.5 mm gap.
• Medium thickness: Around 0.35 mm line width.
• Consistent pattern: To maintain recognition.
• Follow BS 8888 and ISO 128: For uniformity.
• Never used for visible edges: Only for concealed features.

Drawing Broken Lines in Automotive Drawings

1. Identify hidden features such as bolt holes behind a flange.
2. Use a 0.35 mm pen or pencil.
3. Draw short dashes 3 mm long separated by 1.5 mm gaps.
4. Maintain straight or curved lines depending on the hidden feature shape.
5. Ensure lines do not intersect with visible edges.
6. Label hidden features if necessary for clarity.

Significance in Automotive Assembly and Repair

• Helps technicians locate internal engine parts without disassembly drawings.
• Indicates hidden weld lines on chassis frames.
• Reveals internal fluid channels in brake calipers.
• Assists in visualizing gear teeth not visible in external views.
• Supports quality control by showing concealed inspection points.

2.1.4 Chain Lines

Chain lines indicate special features such as centre of gravity, paths of motion, or cutting planes in sectional views.

Purpose of Chain Lines

• Mark cutting planes: Show where a component is sectioned.
• Indicate movement paths: For rotating or sliding parts.
• Highlight symmetry axes: Apart from centre lines.
• Identify limits of tolerance zones: In precision parts.
• Distinguish special features: From visible and hidden edges.

Characteristics and Standards

• Alternating long and short dashes: Commonly 6 mm long dash, 2 mm short dash.
• Medium thickness: Around 0.5 mm line width.
• Clear and distinguishable: To avoid confusion.
• Conform to BS 8888 and ISO 128.
• Accompanied by labels: Such as ‘Section A-A’.

Drawing Chain Lines in Automotive Drawings

1. Determine the feature to be marked (e.g., section plane).
2. Use a 0.5 mm pen or pencil.
3. Draw alternating long (6 mm) and short (2 mm) dashes.
4. Connect dashes smoothly along the required path.
5. Add arrows at ends to indicate direction.
6. Label the line according to drawing conventions (e.g., ‘Cutting Plane A-A’).

Application in Automotive Engineering

• Defines sectional views of engine blocks or transmissions.
• Shows pivot paths for suspension components.
• Marks tolerance zones for brake disc thickness.
• Highlights axes of rotating shafts.
• Indicates limits for welding or machining operations.

2.1.5 Centre Lines

Centre lines locate the geometric centre of circles, arcs, and symmetrical parts in automotive drawings.

Meaning and Purpose

• Identify symmetry axes: For parts like wheels and brake discs.
• Locate centres of holes and cylinders: Essential for drilling and machining.
• Aid in dimensioning: Provide reference points.
• Guide assembly alignment: Ensure correct part positioning.
• Support inspection and quality control: By defining exact centres.

Characteristics and Standards

• Alternating long and short dashes: Typically 6 mm dash and 3 mm gap.
• Thin line: Around 0.18 mm thickness.
• Extend beyond the feature: To indicate centre clearly.
• Conform to BS 8888 and ISO 128.
• No arrows or labels usually: Simple and universally recognized.

Drawing Centre Lines in Automotive Technical Drawings

1. Identify the feature requiring a centre line (e.g., wheel hub).
2. Use a 0.18 mm pen or pencil.
3. Draw alternating long and short dashes along the axis.
4. Extend the line beyond the feature’s edges.
5. Ensure line is straight and continuous.
6. Cross centre lines if needed for intersecting features.

Importance in Vehicle Component Fabrication

• Ensures precise drilling of bolt holes on engine flanges.
• Aligns parts during gearbox assembly.
• Helps in balancing rotating components like crankshafts.
• Assists in verifying symmetry of brake rotors.
• Supports CAD modelling and CNC programming.

2.1.6 Cutting Lines

Cutting lines indicate the location where a sectional view is taken, showing internal details of automotive components.

Purpose and Importance

• Define sectional views: Reveal hidden interior structure.
• Clarify complex assemblies: Show internal features like oil channels.
• Assist in manufacturing: Provide machining details.
• Support maintenance manuals: Help technicians understand part internals.
• Improve drawing readability: By separating external and internal views.

Characteristics and Standards

• Thick chain line with arrows: Typically 0.5 mm thickness.
• Arrows indicate viewing direction: Point to the sectioned area.
• Labeled with letters or numbers: For reference in sectional views.
• Conform to BS 8888 and ISO 128.
• Continuous along the cut path: Without breaks.

Drawing Cutting Lines in Automotive Engineering

1. Identify the part to section (e.g., cylinder head).
2. Select the cutting plane location.
3. Draw a thick chain line along the cutting path.
4. Add arrows at both ends pointing toward the section view.
5. Label the cutting line with a letter or number (e.g., A-A).
6. Ensure the line is clear and does not overlap other lines.

Usage in Automotive Repair and Design

• Sectional views of pistons to show ring grooves.
• Internal views of fuel injectors for maintenance.
• Cross-section of brake calipers for pad replacement.
• Engine block internal coolant passages.
• Transmission gear assemblies to show tooth profiles.

Chapter Summary

This chapter covered the essential types of lines used in technical drawings, including border lines, faint continuous lines, broken lines, chain lines, centre lines, and cutting lines, each serving a distinct purpose in conveying design intent. It detailed the step-by-step construction of various angles such as acute, right, reflex, obtuse, and straight angles, providing foundational skills for accurate geometric representation. The bisection of these angles was also explained, enabling precise division of angles into equal parts for complex constructions. Measurement techniques for all angle types were described to ensure correct reading and replication in drawings. The chapter then focused on constructing plane geometric forms including triangles, quadrilaterals, polygons, as well as circles and their tangents, emphasizing accuracy and adherence to standards. Finally, it introduced the construction of different scales used in technical drawing, covering plane scales, diagonal scales, and methods for reducing and enlarging scales, which are crucial for representing objects proportionally on paper. Together, these topics build a comprehensive foundation for producing clear, precise, and standard-compliant plane geometry drawings.