ENGINEERING GRAPHICS 1E9

Lecture 3 Monday, 15 December 2014 1 ENGINEERING GRAPHICS 1E9 Lecture 3: Isometric Projections

Lecture 3 Monday, 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

Lecture 3 Monday, 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

Lecture 3 Monday, 15 December 2014 4 Types of Axonometric Projections Isometric Projection Dimetric Projection Trimetric Projection

Lecture 3 Monday, 15 December 2014 5 Isometric Projections All angles between axonometric axes are equal The three coordinate axes of the object appear equally foreshortened (about 3/4 th of true length) The angles between any two of the three coordinate axes is 120

Lecture 3 Monday, 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

Lecture 3 Monday, 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)

Lecture 3 Monday, 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

Lecture 3 Monday, 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.

Lecture 3 Monday, 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

Lecture 3 Monday, 15 December 2014 11 Steps: Step 3 Draw the font face of the isometric block.

Lecture 3 Monday, 15 December 2014 12 Steps: Step 4 Draw the rest of the isometric block.

Lecture 3 Monday, 15 December 2014 13 Step 5 Steps: Add details to the block starting from the front face. Then add details to the other faces.

Lecture 3 Monday, 15 December 2014 14 Step 6 Steps: Darken all visible lines to complete the isometric sketch. (make sure that construction lines are light)

Lecture 3 Monday, 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

Lecture 3 Monday, 15 December 2014 16 Objects with Normal Surfaces Make an Isometric Drawing with corner A at the bottom

Lecture 3 Monday, 15 December 2014 17 Objects with Normal Surfaces

Lecture 3 Monday, 15 December 2014 18 Objects with Oblique Surfaces Make an Isometric Drawing with corner A at the bottom NON-ISOMETRIC LINE

Lecture 3 Monday, 15 December 2014 19 Objects with Oblique Surfaces

Lecture 3 Monday, 15 December 2014 20 Objects with Non-isometric Lines Make an Isometric Drawing with apex A facing front

Lecture 3 Monday, 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)

Lecture 3 Monday, 15 December 2014 22 Irregular Objects Make an Isometric Drawing of the following irregular object (pyramid)

Lecture 3 Monday, 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

Lecture 3 Monday, 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???

Lecture 3 Monday, 15 December 2014 25 Approximate Ellipse Draw the isometric centre lines of the circle. Using the centre lines, draw an isometric square with sides equal to the diameter of the circle. From the near corners of the box, draw two large arcs with radius R, using the two red points as centres. Draw the two smaller arcs with radius r, using two green points as centres.

Lecture 3 Monday, 15 December 2014 26 Cylinder

Lecture 3 Monday, 15 December 2014 27 Objects with Circular Geometry

Lecture 3 Monday, 15 December 2014 28 Objects with Non-Circular Curved Surfaces Make an Isometric Drawing of the following curved object

Lecture 3 Monday, 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.