PDT176 COMPUTER-AIDED DRAFTING CHAPTER 5 ISOMETRIC DRAWING

CONTENT Axonometric Drawings Isometric Projections Isometric Sketching

5.1 Axonometric Drawings 1) Introduction Axonometric projection is a parallel projection technique used to create a pictorial drawing of an object by rotating the object on an axis relative to a projection.

5.1 Axonometric Drawings Introduction (cont.)

None of angles are equal. 5.1 Axonometric Drawings 2) Axonometric Drawing Classification (a) Trimetric (b) Dimetric (c) Isometric None of angles are equal. Two angles are equal. All angles are equal.

5.2 Isometric Projections Rotate 45 about vertical axis Tilt forward (35o16’) 1) Theory of Isometric Projection The object is rotated 45 degrees about one axis and 35 degrees 16 minutes on another axis.

Isometric Projection: 5.2 Isometric Projections 2) Isometric Projection vs. Isometric Drawing Isometric Projection: A view produced using a scale of 0.8. Isometric Drawing: A view produced using full scale.

Reverse Axis Isometric from the right (or left) 5.2 Isometric Projections 3) Isometric Drawings An isometric drawing is an axonometric pictorial drawing for which the angle between each axis equals 120 degrees and the scale used is full scale. Isometric axes can be arbitrarily positioned to create different views of a single object. Regular Isometric Reverse Axis Isometric Long Axis Isometric View point is looking down on the top of the object. View point is looking up on the bottom of the object. View point is looking from the right (or left) of the object.

5.2 Isometric Projections Isometric Drawings (cont.) True-length distances are shown along isometric lines. Isometric line is the line that run parallel to any of the isometric axes. Nonisometric lines is the inclined and oblique lines and cannot be measured directly. Isometric lines Nonisometric lines Isometric axes

5.2 Isometric Projections Isometric Drawings (cont.) Center lines Hidden lines Hidden Lines: Are omitted unless they are absolutely necessary to completely describe the object. Center Lines: Are drawn only for showing symmetry or for dimensioning.

5.3 Isometric Sketching 1) Boxing-In Method (Normal Surfaces) Step 1 Draw the isometric axes. Step 2 Create the front isometric plane using W and H dimensions. Multiview Projection

5.3 Isometric Sketching Boxing-In Method (Normal Surfaces) (cont.) Step 3 Create the top isometric plane using W and D dimensions. Step 4 Create the right side isometric plane using D and H dimensions. Step 5 Transfer some distances for the various features from the multiview drawing to the isometric rectangle.

5.3 Isometric Sketching Boxing-In Method (Normal Surfaces) (cont.) Step 6 Transfer the remaining features from the multiview drawing to the isometric drawing. Step 7 Darken all visible lines, and erase or lighten the construction lines.

Example 5.1 The following figure shows the top, front and right-side views of a part in Third Angle Projection. Draw an isometric view of the part in full scale. You must decide the most suitable view as the frontal plane of the isometric drawing. All dimensions are shown in millimeters (mm).

Example 5.1

5.3 Isometric Sketching 2) Nonisometric Lines Step 1 Draw the isometric axes. Step 2 Create the front isometric plane using W and H dimensions.

5.3 Isometric Sketching Nonisometric Lines (cont.) Step 3 Create the top isometric plane using W and D dimensions. Step 4 Create the right side isometric plane using D and H dimensions. Step 5 Transfer the distances for C and A to the top and right side isometric rectangles. Draw line 1 – 2. A C

5.3 Isometric Sketching Nonisometric Lines (cont.) Step 6 Mark off the distance B, and locating points 4 and 3. Connect point 4 – 3. Step 7 Connect points 1 – 4 and 2 – 3 to draw the nonisometric lines.

Example 5.2 The following figure shows the top, front and right-side views of a part in Third Angle Projection. Draw an isometric view of the part in full scale. You must decide the most suitable view as the frontal plane of the isometric drawing. All dimensions are shown in millimeters (mm).

Example 5.2

5.3 Isometric Sketching 3) Oblique Planes Step 1 Draw the isometric axes. Step 2 Create the front isometric plane.

5.3 Isometric Sketching Oblique Planes (cont.) Step 3 Create the top isometric plane. Step 4 Create the right side isometric plane. Step 5 Locate the slot across the top plane.

5.3 Isometric Sketching Oblique Planes (cont.) Step 6 Step 7 Step 8 Locate the endpoints of the oblique plane in the top plane by locating distances A, B, C and D. Locate distance H in the front plane and distance I in the profile plane. Connect all respected lines. Step 7 Draw a line from point 4 parallel to line 7 – 8. Draw a line from point 1 parallel to line 5 – 6. Step 8 Darken all lines.

5.3 Isometric Sketching 4) Angles Step 1 Draw the isometric axes. Create the front, top and right isometric plane. Multiview Projection

5.3 Isometric Sketching Angles (cont.) Step 3 Determine dimensions X and Y. Project both dimensions to create point Z (intersection point). Step 4 Draw lines from point Z to the upper corners in the front plane. Repeat the same step for the back plane to complete the drawing.

5.3 Isometric Sketching 5) Ellipses In isometric drawing, a circle appears as an ellipse. The minor diameter of the ellipses always coincides with the axis of the cylinder, and the major diameter of the ellipse is always at right angles to the minor diameter. There are three methods to draw isometric ellipses; True ellipse construction. Approximate four-center ellipse construction. Isometric ellipse templates.

5.3 Isometric Sketching 5b) Approximate Four-Center Ellipse Construction Step 1 Construct an isometric equilateral parallelogram (sides equal) to the diameter of the circle. Step 2 Find the midpoint of each side of the parallelogram. From that, draw a line to the closest endpoint of the opposite side. Multiview Projection

5.3 Isometric Sketching Approximate Four-Center Ellipse Construction (cont.) Step 3 Draw two small arcs with radius r (centers: A and B). Then, draw two large arcs with radius R (centers: C and D). Step 4 Draw isometric box. Project arc center points A’, B’ and C’. Step 5 Construct the isometric ellipse on the rear face. Add tangent lines.

5.3 Isometric Sketching 6) Arcs Step 1 Step 2 Step 3 Multiview Drawing Construct isometric box. Draw the parallelogram with the sides equal to the diameter of the arc. Step 2 Construct the bisector. Then, construct the isometric half-circle. Step 3 Project center points 1 and 2 to a distance equal to the thickness (T) of the object. Multiview Drawing

Example 5.3 The following figure shows the top, front and right-side views of a part in Third Angle Projection. Draw an isometric view of the part in full scale. You must decide the most suitable view as the frontal plane of the isometric drawing. All dimensions are shown in millimeters (mm).

Example 5.3