Chapter 5-Isometric Drawing PDF

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Drawing 1 Notes

isometric drawing

Department of Civil Engineering

Page 1

Drawing 1

Isometric Drawing - Principles

by: M. Patrick ©

Remember we have just worked on the set of rules called "Orthographic Projection" which allowed us to take a three dimensional object, or a picture and draw it in a form where it had a "Front, Side and Top" view or "Elevation". We are now going to work in reverse - from the three "Orthographic Views" (Front Elevation - Side Elevation - Plan), we are now going to produce a "Three dimensional" drawing or a picture. Uses of pictorial Drawings Pictorial drawings are excellent aids in the design process, for they allow designers and engineers to view the objects at various stages in their development. Pictorial drawings are used in instruction manuals, parts catalogues, advertising literature, technical reports and presentations and as aids in the assembly and construction of products. Types of Pictorial Drawings Artists like Michelangelo and Leonardo da Vinci use a process called "Perspective Drawing" where at least two vanishing points are required - this process is very realistic and life like and equally complicated. The most common forms of pictorial drawing used in engineering drawing are "isometric" and "oblique". These two basic forms of pictorial drawing are easy to master, if you can visualize objects in orthographic projection and three dimensions. ISOMETRIC PROJECTION The word ISOMETRIC means equal (iso) measure (metric). The three principal planes and edges make equal angles with the plane of projection . Procedure Three steps are used in making the Isometric drawing from the Orthographic drawings given (Front view and plan). 1) Make an isometric rectangular box that will contain the object by drawing three lines, one vertical, and the other two each at 30° to the horizontal. Along these lines, mark off the height, length and breadth. (use construction lines at first) 2) Along the appropriate edges of the "box" mark off the dimensions given. 3) Darken-in the outline and indicate the hidden detail by means of dotted lines. (broken lines)

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Department of Civil Engineering

Page 2

Drawing 1

Isometric Drawing - Principles

by: M. Patrick ©

Procedure Three steps are used in making the Isometric Drawing from The Orthographic drawings (Front view and plan). - Repeat the same three steps producing an isometric drawing for this example.

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Exercises Adopting the three steps we have just learnt, draw an isometric view of each of the other objects below. Do not dimension them but show all hidden detail with dashed lines. Neatly Title each one "FIG ?" with it's appropriate number.

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FIG. 2

FIG. 3

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FIG. 1

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FIG. 4 Department of Civil Engineering

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FIG. 5

Page 3

Drawing 1

Isometric Drawing - Principles

by: M. Patrick ©

Circles in Isometric In an isometric drawing, a circle will appear as an ellipse. Fig 1 Shows an orthographic view of a 50mm diameter circle enclosed in a square (not to scale)

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Procedure Five steps in drawing the circle (Fig 1) in Isometric on the 3 planes, A, B, & C as seen on the cube are shown below. Ø50

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Fig.1

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The same steps are repeated for all faces, A, B & C. int po

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120° Obtuse angle

Acute angle 60°

mid-point

mid-point

dmi

Repeat the same process from the other obtuse angle.

Draw a line from the obtuse angle to the opposite mid-point

30° mid-point

Place your compass point where the lines intersect (circled) and draw the small arc as shown. Repeat where the other two lines intersect.

Now place your compass point at the apex of the obtuse angles (circled) and draw the long arcs to complete the ellipse.

B Draw a line from the obtuse angle to the opposite mid-point

Acute angle 60°

mid-point

120° Obtuse angle

mid-point

mid-point

Place your compass point where the lines intersect (circled) and draw the small arc as shown. Repeat where the other two lines intersect.

Repeat the same process from the other obtuse angle.

30° mid-point

C 30°

mi dmid-point

po int

mid-point

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dmi

int po

Now place your compass point at the apex of the obtuse angles (circled) and draw the long arcs to complete the ellipse.

Page 4

Drawing 1

Isometric Drawing - Principles

by: M. Patrick ©

Exercises Fig 2 shows two orthographic views of a cylinder resting on a square base and FIG 3 illustrates two steps in making an isometric drawing of the combination. Try it!

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Fig.3

Fig.2

Exercises Fig 4 to 6 below are other items involving isometric circles being quite a challenge to some!

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Note: The above exersises must be completed before the test.

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