LessonnotesGH

SHS3 Manufacturing Engineering · Semester 1, Week 14

Design and Drawing for Manufacture

Lesson notes

Learning Objectives

Indicator: 3.2.1.LI.2 - Explain the application of limits and fits in production drawing.

By the end of the lesson, learners can:

  1. Define the key terms related to limits and fits: tolerance, limits, deviation, upper deviation, lower deviation, and allowance, using examples from actual production drawings.
  2. Interpret the zone line and standard tolerance grades (IT01 to IT18) as shown on a production drawing and explain how they control the size of a component.
  3. Distinguish between hole basis and shaft basis systems for fits and explain when each is selected for a manufacturing task.
  4. Apply the step-by-step procedure (select fit, select shaft and hole type, select tolerance grade, evaluate standard tolerance, evaluate limits and tolerance) to calculate the limits and tolerances for a given component.
  5. Justify the selection of a particular fit (clearance, interference, or transition) for a given functional requirement, such as a bearing on a shaft or a key in a keyway.

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Curriculum details

Strand
Design and Prototyping (Strand 2)
Sub-strand
Design and Drawing for Manufacture (2.1)
Content standard
3.2.1.CS.1 - Demonstrate knowledge and understanding of the importance of the representation of materials and machine components in production drawing. 3.2.1.LO.1 Understand the representation of materials, machine components, limits, and fits in production drawings.
Indicator
3.2.1.LI.2 - Explain the application of limits and fits in production drawing.
Suggested placement
Semester 1, Week 14 (Week 14 of the year)

Our suggestion, laid out in curriculum order across three terms of twelve weeks. NaCCA does not fix the week, so follow your school's scheme of learning.

Curriculum reference
NaCCA curriculum document, p. 85

Exemplars (from the NaCCA curriculum) 

Experiential Learning: Show learners a typical production drawing in class and lead them to identify limits and fits as used in the production drawing.
Collaborative Learning: Learners in mixed-ability groups research on the application of limit systems (such as tolerance, limits, deviation, actual deviation, upper deviation, lower deviation, and allowance) as used in production drawings, and share their findings with the class.
Talk for Learning: Lead learners to discuss zone line, standard tolerances, rules for dimensioning tolerances, hole basis and shaft basis for fits, selection of fits, limit gauges, machining symbols, and an indication of roughness as used in production drawings.
Practice-Based Learning: Learners in mixed-ability groups practice the evaluation of limits and tolerances for a component according to the following steps: selection of appropriate fit based on the functional requirement, selection of the type of shaft and hole, selection of tolerance grade for shaft and hole, evaluation of standard tolerance and evaluation of limits and tolerance.
Teaching and Learning Materials:
- Sample production drawings
- Textbooks
- Library resources
- Internet access
Assessment (3.2.1.AS.2). The document marks these depth-of-knowledge levels for this indicator: Level 1 Recall; Level 2 Skills of conceptual understanding; Level 3 Strategic reasoning; Level 4 Extended critical thinking and reasoning.
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