Fundamentals of
Engineering Drawing
and CAD
Engineering Drawing - Lesson 2
Isometric View
Teaching Plan – Engineering Drawing
Lesson 1
> Principle of engineering
drawing & interpretation in
accordance with standard
> Orthographic projection
(1st angle)
> Orthographic projection
(3rd angle)
• In-class Assignment 1(i)
(60%)
Lesson 2
> Introduction to isometric
projection & isometric
drawing
> Isometric lines
> Isometric circle & arc
• In-class Assignment 1(ii)
(40%)
1
Types of Projection
Projection
Pictorial
Orthographic
1st Angle
AXONOMETRIC
OBLIQUE
3rd Angle
PERSPECTIVE
For Visualization
For Specification
Perspective Projection
THREE-POINT PERSPECTIVE
2
Oblique Projection
Cavalier Oblique
Cabinet Oblique
Axonometric Projection
> It is a projected view in which the lines of sight
perpendicular to the plane of projection.
3
Axonometric Projection
> There are three types of projection.
1) In an isometric projection, equal angles (120°) are
used between each of the primary axes.
• The scales used for each axis are also equal.
2) In a dimetric projection, two of the angles used
between the primary axes are equal.
• Two of the scales for the axes are equal.
3) In a trimetric projection, the axis intersections
produce three different angles.
• Three different scales are used for the axes.
Axonometric Projection
Isometric is the most common.
• Refers to equal measure.
Isometric
Axis lines measured at same scale
Dimetric
• Refers to two measures.
Dimetric
Axis lines measured at two different scales
Trimetric
• Refers to three measures.
Trimetric
Axis lines measured at three different scales
4
Isometric Projection Vs Isometric Drawing
> A style is used to show all three dimensions of an object in a single view
> Isometric View is the quickest and easiest pictorial presentation to draw
> Difference between isometric projection and isometric drawing
Isometric projection: Height, width and depth are displayed at 82% of their true length
Isometric drawing: 100% true length measurements on the height, width and depth axes
100% HEIGHT
•
•
82% HEIGHT
ISOMETRIC DRAWING
ISOMETRIC PROJECTION
The tilt causes the edges & planes
to become foreshortened
(Isometric Projection)
Isometric Drawing Types
>Isometric axes can be arbitrarily positioned to
create different views of a single object.
Regular Axis
Reversed Axis
View point is looking down
on the top of the object.
View point is looking up on
the bottom of the object.
5
Isometric Planes & Isometric Axis
>The three faces of the isometric cube are
isometric planes, because they are parallel to the
isometric surfaces formed by any two adjacent
isometric axes.
Isometric Planes
Isometric Axis
Isometric Lines vs. Non-isometric Plane
• Isometric lines are the lines that run parallel to any of
the isometric axes.
• Planes that are not parallel to any isometric plane are
called non-isometric planes.
Isometric lines and nonisometric plane
Nonisometric plane
6
Non-isometric Lines
> Non-isometric lines are the lines that are not parallel to
any of the iso-lines.
> They are drawn by transferring the distance of X or Y from
multi-view to iso-view, not the actual length itself.
ORTHOGONAL VIEW
L is orthogonal
not equal to L’
in isometric
ORTHOGONAL VIEW
ISOMETRIC VIEW
ISOMETRIC VIEW
(b) Non-isometric lines
(a) Isometric angles
Making an Isometric Sketch
Height
>Step 1: Defining Axis
60o
60o
30o
30o
Isometric Axis
7
Making an Isometric Sketch
>Step 2: Sketch axes on the grid paper
Correct orientation
Incorrect orientation
Note the alignment of the axes
Making an Isometric Sketch
>Step 3: Select view and isometric axis convention
Height
Width
Depth
Choose the longest dimension to
be the width (or the depth) for
optical stability
Isometric Axis Convention
8
Making an Isometric Sketch
>Step 4: Draw the box, begin with Front View
Height
Making an Isometric Sketch
>Step 5: Draw the box, add Side View
Height
9
Making an Isometric Sketch
>Step 6: Draw the box, add Top View
Top view
Making an Isometric Sketch
>Step 7: Draw the box for detail cut 1
10
Making an Isometric Sketch
>Step 8: Draw the box for detail cut 2
Making an Isometric Sketch
>Step 9: Draw the box for detail cut 3
11
Making an Isometric Sketch
>Step 10: All visible edges will be darkened as below
Isometric Circles and Arcs
> Isometric circles or iso-circle cannot be simply drawn
using compass.
> Any iso-circle may lie on either top plane, left (front) plane
or right (profile) plane.
> Iso-circle looks slightly oval and skewed.
Horizontal or
top plane
Major axis
Minor axis
Major axis
Major axis
Minor axis
Minor axis
Front plane
Profile plane
60o
30o
Correct
30o
60o
Incorrect
12
Constructing Isometric Circles
>The four-center method is more efficient than the
coordinate method.
• Plotting coordinates for a circle requires many points
to provide a good shape definition.
• Using arcs and center points on an isometric plane
simplifies the process.
Isometric Circles and Arcs
> Drawing isometric circles and arcs using four-centre
method
(a) Full Circles
(b) Half Circles
c) Quarter Circles
13
Drawing Isometric Circle
•
Step 1: Draw center lines, vertical & 30deg to
left.
•
Step 2: Draw (construction line) 20mm
“square box”. The center lines should divide
each side by half.
Step 3: Draw straight lines; 1-2 & 1-3 and 45 & 4-6
Step 4: Point is the intersection between line
1-2 & 4-5, set your compass to the distance,
draw an arc with point as center
Step 5: Do the same on the other side
Step 6: Similarly set the compass to the
distance at point 4 as center to draw an arc
with from 5 to 6.
Step 7: Do the same on the other side
•
•
•
•
•
To draw an isometric
circle on left plane, 
20mm
5
2
1
4
6
3
Alternative Method
Four-Center Method
> If the arcs do not meet properly, draw a correction
arc.
• Reset the compass to the proper radius of the small
arc.
• Draw arcs from the ends of the large arcs to locate a
new center.
• Draw the arc.
14
Disadvantages of Pictorials
> Present difficulty when dimensions are required for
manufacturing.
> The viewing angle may cause distortion in the object.
> Hidden details may be difficult to visualize.
> Complex shapes may be difficult to draw.
Block-in Technique for Non-isometric Lines
> Nonisometric lines and surfaces require additional steps.
• Draw an isometric block with the overall dimensions.
• Measure distances on each orthographic view and transfer
to points on isometric lines parallel to axis lines on the
block.
• Connect the points with nonisometric lines.
> Nonisometric lines are not true length and cannot be
measured directly with a scale.
Step 1
Step 2
Step 3
15
Block-in Technique for Nonisometric Surfaces
Drawing Isometric Arcs, Circles, and Irregular Curves
> Circles and arcs appear as ellipses in an isometric
drawing.
> The coordinate method simplifies the drawing
process for arcs.
• Points are located on curves using isometric lines as
reference lines.
• An orthographic view is commonly used to transfer
coordinate points.
16
Coordinate Method
> First, “block in” the basic object shape.
> Identify coordinate points on the curved shape in the
orthographic projection.
> Transfer coordinates from the orthographic view to
the corresponding points in the isometric view.
> Connect the points in a smooth curve with an
irregular curve or spline.
> Locate points on the closest surface first, then
background features.
Coordinate Method
17
Reference
> Cecil Jensen, Jay D. Helsel, Dennis R. Short. (2008),
Engineering drawing & design (7th ed.) McGraw-Hill
Higher Education, New York.
> David L. Goetsch (2005), Technical drawing (5th ed.),
Thomson/Delmar Learning, Clifton Park, N.Y.
> Colin H. Simmons, Dennis E. Maguire, Neil Phelps
(2009), Manual of engineering drawing (3rd ed.),
Newnes, Amsterdam ; Boston ; London.
In-class Assignment 1(ii)
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