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Lecture 3Monday, 15 December 2014 1
ENGINEERING GRAPHICS1E9
Lecture 3: Isometric Projections
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Lecture 3Monday, 15 December 2014 2
What is ISOMETRIC?
• It is a method of producing pictorial view of an object showing all three faces of the
object simultaneously.
• It is a type of parallel projection
• It is a type of axonometric projection
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Lecture 3Monday, 15 December 2014 3
Axonometric Projections
• Observer at infinity
• Projectors parallel to each other and perpendicular to projection plane
• Object is inclined with respect to projection plane
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Lecture 3Monday, 15 December 2014 4
Types of Axonometric Projections
Isometric Projection
Dimetric Projection
Trimetric Projection
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Lecture 3Monday, 15 December 2014 5
Isometric Projections
• All angles between axonometric axes are equal
• The three coordinate axes of the object
appear equally foreshortened (about 3/4th
of true length)
• The angles between any two of the three coordinate axes is 120°
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Lecture 3Monday, 15 December 2014 6
Isometric Terminology
• The three coordinate axes are called isometric axes
• Any line parallel to isometric axes is called isometric line
• A non-isometric line is a line not
parallel to any one of the three isometric axis
• In isometric projection of cube, the faces of the cube and any plane parallel to them is
called isometric planes
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Lecture 3Monday, 15 December 2014 7
Isometric Scale
• True lengths of the edges of the object are equally foreshortened
• Correct isometric projection can be drawn using an isometric scale (always smaller
than ordinary scale)
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Lecture 3Monday, 15 December 2014 8
Isometric Drawing
Isometric Projection: Drawing prepared
with isometric scale on
isometric axes
Isometric Drawing:
Drawing prepared with ordinary scale
on isometric axes
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Lecture 3Monday, 15 December 2014 9
Steps:
Step 1
Isometric sketches begin with defining
isometric axes, three lines, one vertical and two drawn at 30° from the horizontal.
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Lecture 3Monday, 15 December 2014 10
Steps:
Step 2
Three lines of the isometric axes represent
the three primary dimensions of the object: width, height, and depth
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Lecture 3Monday, 15 December 2014 11
Steps:
Step 3
Draw the font face of the isometric block.
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Lecture 3Monday, 15 December 2014 12
Steps:
Step 4
Draw the rest of the isometric block.
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Lecture 3Monday, 15 December 2014 13
Steps:
Step 5
Add details to the block starting from the
front face. Then add details to the other faces.
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Lecture 3Monday, 15 December 2014 14
Steps:
Step 6
Darken all visible lines to complete the
isometric sketch. (make sure that construction lines are light)
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Lecture 3Monday, 15 December 2014 15
• Axonometric projection shows all 3 dimensions, length, width and height.
• The isometric lines are only drawn to scale. Objects composed entirely of isometric lines can be drawn by taking all measurements parallel to main edges of the enclosing box.
• Non-isometric lines are drawn by transferring the ordinates (which are on isometric lines) of the end of the lines
• Inclined and oblique surfaces are drawn using end coordinates. Box construction and offset measurements are common methods
• In an isometric drawing, an angle never appears in its true size. Angles, irregular curves require special techniques
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Lecture 3Monday, 15 December 2014 16
Objects with Normal Surfaces
Make an Isometric Drawing with corner A at the bottom
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Lecture 3Monday, 15 December 2014 17
Objects with Normal Surfaces
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Lecture 3Monday, 15 December 2014 18
Objects with Oblique Surfaces
• Make an Isometric Drawing with corner A at the bottom
NON-ISOMETRIC LINE
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Lecture 3Monday, 15 December 2014 19
Objects with Oblique Surfaces
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Lecture 3Monday, 15 December 2014 20
Objects with Non-isometric Lines
• Make an Isometric Drawing with apex A facing front
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Lecture 3Monday, 15 December 2014 21
Objects with Non-isometric Lines
Non-isometric lines are drawn with box construction and offset measurements
Non-isometric lines are not drawn in true length in isometric drawing (BA is shorter than CA in this drawing)
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Lecture 3Monday, 15 December 2014 22
Irregular Objects
• Make an Isometric Drawing of the following irregular object (pyramid)
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Lecture 3Monday, 15 December 2014 23
Irregular Objects
• OA and OB offsets help to locate apex O
• Complete box construction may not be needed in each case
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Lecture 3Monday, 15 December 2014 24
Objects with Circular Geometry
A circle in a orthographic projection will appear as an ellipse in an isometric drawing.
Instead of actual ellipses often approximate ellipses are drawn for isometric drawing.
Four-centre ellipses are used to approximate ellipses on isometric planes.
How to draw four-centre ellipse???
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Lecture 3Monday, 15 December 2014 25
Approximate Ellipse
•Draw the isometric centre lines of the circle.Using the centre lines, draw an isometric square with sidesequal to the diameter of the circle.•From the near corners of the box, draw two large arcs withradius R, using the two red points as centres.•Draw the two smaller arcs with radius r, using two green pointsas centres.
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Lecture 3Monday, 15 December 2014 26
Cylinder
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Lecture 3Monday, 15 December 2014 27
Objects with Circular Geometry
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Lecture 3Monday, 15 December 2014 28
Objects with Non-Circular Curved Surfaces
• Make an Isometric Drawing of the following curved object
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Lecture 3Monday, 15 December 2014 29
Objects with Non-Circular Curved Surfaces
•A line that appears as a noncircular curve in a normal orthographic view of an object appears as a non-isometric line in an isometric drawing.
•Curves may be drawn using a series of points by measuring along the normal lines in the orthographic view (offset measurements) and transferring these points on isometric drawing. Accuracy increases with number of points.