Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Apply SANS drawing conventions for dimensioning and tolerance.
• Interpret and answer questions from past EGD exam papers.
• Apply first-angle and third-angle orthographic projection.
• Draw and interpret surface development for geometric shapes.
• Interpret and draw cams and gears to specification.

Lesson summary

This week marks a critical point in our Grade 12 EGD journey: focused revision and preparation for upcoming assessments, especially the end-of-year examinations. EGD isn't just about drawing lines; it's about visually communicating ideas, a skill crucial in various South African industries, from architecture and engineering to manufacturing and design. Understanding EGD principles allows you to interpret plans for building infrastructure, design sustainable housing solutions, or even contribute to the creation of innovative products that address local needs.

Lesson notes

This week's revision will cover key concepts within the Grade 12 EGD syllabus, focusing on common areas of difficulty. We will address these concepts through the lens of past papers and real-world examples. 2.

1. SANS Drawing Conventions (Dimensioning and Tolerances)

Concept: South African National Standards (SANS) dictate the rules for creating clear and unambiguous engineering drawings. SANS 10111 is particularly important and should be referred to throughout the year. Accurate dimensioning is vital for manufacturing and construction, ensuring parts fit together correctly. Tolerances specify the allowable variation in size, which is essential for mass production and interchangeable parts. These standards are incredibly relevant when thinking about manufacturing anything locally. A poorly dimensioned drawing can easily lead to costly errors and delays, affecting the efficiency and affordability of South African manufacturing projects.

Dimensioning: Dimensions indicate the size and location of features. Use continuous, chain, or parallel dimensioning techniques depending on the drawing. Remember extension lines, dimension lines, arrowheads, and dimension values. Ensure all dimensions are clear, concise, and placed outside the object whenever possible.

Tolerances: Tolerances specify the acceptable variation in dimensions. General tolerances apply to undimensioned features, while specific tolerances apply to dimensioned features. Common tolerance notations include unilateral (e.g., +0.1/-0), bilateral (e.g., ±0.05), and limit dimensions (e.g., 25.00/25.10). Consider the function of the part when specifying tolerances. Parts that need to fit together precisely will have tighter tolerances.