# Lesson Notes By Weeks and Term - Senior Secondary 1

Dimensioning

TERM – 3RD TERM

WEEK SIX

Class: Senior Secondary School 1

Age: 15 years

Duration: 40 minutes of 5 periods each

Date:

Subject: Technical Drawing

Topic: DIMENSIONING

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

I.) Define dimensioning

II.) Describe the types of dimensioning

III.) Discuss the dimensioning rules.

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures,

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

 PRESENTATION TEACHER’S ACTIVITY STUDENT’S ACTIVITY STEP 1 INTRODUCTION The teacher explains the meaning of dimensioning and identify the types of dimensioning in Technical drawing. Students listens attentively to the teacher STEP 2 EXPLANATION Teacher discusses the rules for dimensioning. Students exhibit attentiveness and active engagement STEP 3 NOTE TAKING The teacher writes a summarized note on the board The students copy the note in their books

NOTE

DIMENSIONING

Dimensioning refers to the process of adding measurements, notes, and annotations to a drawing to specify the size, location, and other details of objects or features depicted in the drawing.

Methods of dimensioning

The following are the methods of dimensioning for various shapes( Circles, arcs, chamfers, horizontal, vertical and angular shapes)

1. Circles and Arcs: Diameter dimensioning is commonly used for circles, while arcs are dimensioned with their radius or diameter. Arcs can also be dimensioned by specifying their center point, start point, and end point.

2. Chamfers: Chamfers are typically dimensioned by indicating the distance from the corner to the start of the chamfer and the angle of the chamfer.

3. Horizontal and Vertical Shapes: For horizontal and vertical shapes, dimensions are straightforward, indicating lengths, widths, or heights. Horizontal dimensions are aligned parallel to the horizontal axis, and vertical dimensions are aligned parallel to the vertical axis.

4. Angular Shapes: Angular dimensions specify the angle formed by lines or edges. These dimensions are usually indicated with a symbol (like a degree symbol) and the measurement of the angle.

Dimensioning Rules

1. Extension lines place at the ends of a dimension lines do not touch the body of the object it is dimensioning.
2. Extension lines do not also cross each other where dimensioning requires that the cross one another. Hence, one of the extension lines has to be broken to allow the other to pass.
3. When dimensioning a slant or inclined side or line on an object, the back of the arrow head is slightly adjusted to be parallel with the extension lines placed at the ends of the dimension line.
4. When dimensioning a circle, the tip of the arrow head is made to point to the center of the circle and not any other direction. Or, the dimension line used must through the center of the circle.
5. All measurements in technical drawing are in millimeters unless otherwise stated.
6. The symbol ∅ and M when placed behind a number represent the same thing-diameter of a hole or a thread. ∅24 means common or ordinary hole of diameter 24mm. But M24 represents the Metricdiameter of a screw thread of value 24mm.

EVALUATION: 1. What is dimensioning

1. Identify and discuss the types of dimensioning
2. Mention 5 rules of dimensioning.

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively