Preparing and interpreting technical drawing

WEB SCRIPT Electrical and Electronics
Sector: Electronics Products Assembly and Servicing NC II
Qualification: Prepare and Interpret Technical Drawing
Unit of Competency:
Module Title: Preparing and Interpreting Technical Drawing
Learning Outcomes: LO2: Interpret technical drawings
Developer/s: Anna Marie D. Gime

TITLE Interpreting technical drawings
OBJECTIVES In this lesson the learners will be able to Interpreting technical drawings,
and the different types of lines and its mean.
INTRODUCTION
Alphabet of Lines (all the information is based to LinkedIn Corporation
Topic 2 © 2020)
Lesson 1
 Lines are the critical component of sketching.
 Lines have different types, thickness and shape has its own

meaning
 Alphabet of Lines are also known as b“Line symbols”

Ways to interpret Technical Works
Alphabet of line

Source: LinkedIn Corporation © 2020

Examples of Lines

Source: LinkedIn Corporation © 2020

LinkedIn Corporation © 2020

Application using of alphabet lines in drawing

1.1 Types of Alphabet Symbols

Source: LinkedIn Corporation © 2020

OBJECT OR VISIBLE LINE
Thick, dark line used to show the outline of the object. Define features you can see in a particular
view.

Source: LinkedIn Corporation © 2020

CONSTRUCTION LINE
Lines that are very light and very thin are used to construct layout work.

Source: LinkedIn Corporation © 2020

DIMENSION LINE
Thin and dark lines are used to show the size (span) of an object with a numeric value. Usually
terminates with arrowheads or tick markings.

Source: LinkedIn Corporation © 2020

HIDDEN LINE
Short dash lines are used to show non visible surfaces that are not visible in orthographic view.
Usually shows as medium thickness.

Source: LinkedIn Corporation © 2020

CENTRE LINE
Long and short dash lines. Usually indicates the centre of holes, circles and arcs. Line is thin and dark.

Source: LinkedIn Corporation © 2020

EXTENSION LINE
A light line that extends from the edge or end of a main object line on a drawing, used in conjunction with
dimension lines to help determine the dimension of a particular feature.

Source: LinkedIn Corporation © 2020

CUTTING PLANE LINE
Extra thick lines are used to show cutaway views or planes of projection where a section view is
taken. Arrow indicates direction of view.

Source: LinkedIn Corporation © 2020

LEADER LINE
A thin line used to connect a dimension line with a particular area or point on the drawing. It is also
used to show notes or labels.

Source: LinkedIn Corporation © 2020

PHANTOM LINE
Long line followed by two short dashes used to show alternate positions of a moving part.

Source: LinkedIn Corporation © 2020

Example of short-break and long-break line

SHORT-BREAK LINE

Thick wavy line that is used to break the edge of a surface of a part for clarity on a hidden surface.

LONG-BREAK LINE
Long, thin lines that are used to show that the middle section of an object has been removed so it
can be drawn on a smaller piece of paper.

Quiz 3: IDENTIFICATION TYPE

Direction: Read and Identify the following question and answer it on the space provided.
_______________________1. Lines are the critical component of sketching.
_______________________2. Extra thick lines are used to show cutaway views or planes of
projection where a section view is taken. Arrow indicates direction of view.
_______________________3. Long, thin lines that are used to show that the middle section of an
object has been removed so it can be drawn on a smaller piece of paper.
_______________________4. Long line followed by two short dashes used to show alternate
positions of a moving part.
_______________________5. A light line that extends from the edge or end of a main object line
on a drawing, used in conjunction with dimension lines to help determine the dimension of a
particular feature.
_______________________6.Long and short dash lines. Usually indicates the centre of holes,
circles and arcs. Line is thin and dark.
_______________________7.Thin and dark lines are used to show the size (span) of an object
with a numeric value. Usually terminates with arrowheads or tick markings.
_______________________8. A thin line used to connect a dimension line with a particular area or

point on the drawing. It is also used to show notes or labels.
_______________________9.Short dash lines are used to show non visible surfaces that are not
visible in orthographic view. Usually shows as medium thickness.

_______________________10.Thick, dark line used to show the outline of the object. Define
features you can see in a particular view.

Answer Key of IDENTIFICATION TYPE

1. Alphabet of lines
2. Cutting Plane lines
3. Long break lines
4. Phantom lines
5. Extension Lines
6. Centre Lines
7. Dimension lines
8. Leader Lines
9. Hidden Lines

10. Objector or Visible Line

Lesson 2 Orthographic Projection

Orthographic Projections

Orthographic Projections are a collection of 2-D drawings that work together to give an accurate
overall representation of an object.

Defining the Six Principal Views or Orthographic Views
General Guidelines

• Pick a Front View that is most descriptive of object
• Normally the longest dimension is chosen as the width (or depth)
• Most common combination of views is to use:

– Front, Top, and Side View









Glass Box Approach

 Place the object in a glass box

 Freeze the view from each direction (each of the six sides of the box) and unfold the
box

2.1 Dimensioning
Lines on an engineering drawing signify more than just the geometry of the object and it is
important that the appropriate line type is used.

 Line Thickness
For most engineering drawings you will require two thickness', a thick and thin line. The general
recommendation are that thick lines are twice as thick as thin lines.

A thick continuous line is used for visible edges and outlines.

A thin line is used for hatching, leader lines, short centre lines, dimensions and projections.

 Line Styles
Other line styles used to clarify important features on drawings are:

Thin chain lines are a common feature on engineering drawings used to indicate centre lines.
Centre lines are used to identify the centre of a circle, cylindrical features, or a line of symmetry.

Dashed lines are used to show important hidden detail for example wall thickness and holes.

 Precedence of Lines
0.6mm

 Visible lines takes precedence over all other lines
0.3mm

 Hidden lines and cutting plane lines take precedence over centerlines
0.6mm

 Center lines have lowest precedence

 Dimensioning
A dimensioned drawing should provide all the information necessary for a finished product or part
to be manufactured. An example dimension is shown below.

Dimensions are always drawn using continuous thin lines. Two projection lines indicate where the
dimension starts and finishes. Projection lines do not touch the object and are drawn perpendicular
to the element you are dimensioning. All dimensions less than 1 should have a leading zero. i.e. .35
should be written as 0.35
Types of dimensioning

 Parallel Dimensioning - Parallel dimensioning consists of several dimensions originating
from one projection line.

 Superimposed Running Dimensions - Superimposed running dimensioning simplifies
parallel dimensions in order to reduce the space used on a drawing. The common origin for the
dimension lines is indicated by a small circle at the intersection of the first dimension and the
projection line.

 Chain Dimensioning - when each single dimension is placed directly adjacent to the next
dimension without any gap between dimensions line. This method should only be used if tolerance
accumulation is not going to affect the function of part.

 Combined Dimensions -A combined dimension uses both chain and parallel dimensioning.

Dimensioning of circles

(a) shows two common methods of dimensioning a circle. One method dimensions the circle
between two lines projected from two diametrically opposite points. The second method
dimensions the circle internally.
(b) is used when the circle is too small for the dimension to be easily read if it was placed
inside the circle.
Dimensioning Radii - All radial dimensions are preceded by the capital R.

(a) shows a radius dimensioned with the centre of the radius located on the drawing.
(b) shows how to dimension radii which do not need their centres locating.
Tolerancing
It is not possible in practice to manufacture products to the exact figures displayed on an
engineering drawing. The accuracy depends largely on the manufacturing process.
A tolerance value shows the manufacturing department the maximum permissible variation from

the dimension. Each dimension on a drawing must include a tolerance value. This can appear
either as: a general tolerance value applicable to several dimensions. i.e. a note specifying that the
General Tolerance +/- 0.5 mm. or a tolerance specific to that dimension

Drawing layout
All engineering drawings should feature a title block.

The title block should include:
Title:- title of the drawing
Name:- name of the person who produced the drawing
Checked:- before manufacture, drawings are usually checked
Version:- many drawings are amended, each revision must be noted
Date:- the date the drawing was produced or last amended
Notes:- any note relevant to the drawing
Scale:- the scale of the drawing

Company name:- name of the company
Projection:- the projection system used to create the drawing

Source: All the information here is base to https://www.slideshare.net/nyioq/orthographic-
projection)
Quiz 4: TRUE OR FALSE :
Direction: Read and Understand the following statement. Write TRUE if the statement is correct
and FALSE if the statement is incorrect regarding Orthographic Projection. Write your answer on
the space provided.
________1. A tolerance value shows the manufacturing department the maximum permissible
variation from the dimension
________2. When each single dimension is placed directly adjacent to the next dimension without
any gap between dimensions line. This method should only be used if tolerance accumulation is not
going to affect the function of part this is called chain dimensioning.
________3. Orthographic Projections are a collection of 3-D drawings that work together to give an
accurate overall representation of an object.
________4. For most engineering drawings you will require no thickness', a thick and thin line. The
general recommendation is that thick lines are twice as thick as thin lines.
________5. A combined dimension uses both chain and parallel dimensioning.
Answer key:

1. True
2. True
3. False
4. False

5. True

ACTIVITY SHEET 1

ALPHABET OF LINES

Learning Outcome: Alphabet of Lines
Activity: Drawing the alphabet of lines
Learning Objective: at the end of this activity the will be able to draw the alphabet of lines neat and
correct.
Time Allotted: 2.5 hrs
Materials and tools needed:
 T-square • Steel rule • Triangles (right angle and isosceles) • Eraser shield • Masking tape

(drafting dots) • Drafting board • drawing pencil • A4 size drawing paper

STEPS:
1. Gather the materials tools listed above.
2. Using the T-square and masking tape/drafting dots, align title-blocked paper to your drafting
board and securely tape down.
3. Make a boarder of 1” all sides. Following the note below create a title block out below the
paper
Note: The title block should include:

 Title:- title of the drawing

 Name:- name of the person who produced the drawing

 Learning Facilitator Name:- the name of the facilitator must be complete

 Course: the qualification where you are enrolled

 Date:- the date the drawing was produced or last amended

1 Inch
boarder

Name Course Learning
Facilitator
Date
Name

Title

4. Copy and draw the alphabet of lines below

.

5. Take a picture and send it to your learning facilitator.

PERFORMANCE CRITERIA CHECKLIST
ACTIVITY SHEET 1

Learner’s Name: ___________________________________ Date: _______________

Did the Learner perform the following… YES NO
1. Gather the materials and tools needed
2. Created the correct title box following the given guide
3. Draw the alphabet of lines neatly and correctly

Learner’s Signature:
Comment/Feedback:

Prepared by:

Anna Marie D. Gime
EPAS – Trainer, BPTI

OUTPUT: LO2: Interpret technical drawings