11/12/2015 CHAPTER 7. Axonometric Drawings (cont.) Axonometric Drawings (cont.) Isometric Projections (cont.) 1) Axonometric Drawings

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1 CHAPTER 7 1) Axonometric Drawings 1) Introduction Isometric & Oblique Projection 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. Introduction (cont.) Axonometric Drawings (cont.) Axonometric Drawings (cont.) 2) Axonometric Drawing Classification (a) Trimetric (b) Dimetric (c) Isometric None of angles are equal. Two angles are equal. All angles are equal. 2) Isometric Projections Isometric Projections (cont.) 1) Theory of Isometric Projection The object is rotated 45 degrees about one axis and 35 degrees 16 minutes on another axis. Rotate 45 about vertical axis Tilt forward (35 o 16 ) 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. 1

2 3) Isometric Drawings Isometric Projections (cont.) Isometric Drawings (cont.) Isometric Projections (cont.) 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 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 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. Isometric Drawings (cont.) Isometric Projections (cont.) 3) Isometric Sketching 1) Boxing-In Method (Normal Surfaces) Hidden lines Center lines Draw the isometric axes. Create the front isometric plane using W and H dimensions. 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. Multiview Projection Boxing-In Method (Normal Surfaces) (cont.) Boxing-In Method (Normal Surfaces) (cont.) Create the top isometric plane using W and D dimensions. Create the right side isometric plane using D and H dimensions. Transfer some distances for the various features from the multiview drawing to the isometric rectangle. 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. 2

3 Example 1 Example 1 (Answer) 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). 2) Nonisometric Lines Nonisometric Lines (cont.) Draw the isometric axes. Create the front isometric plane using W and H dimensions. Create the top isometric plane using W and D dimensions. Create the right side isometric plane using D and H dimensions. Transfer the distances for C and A to the top and right side isometric rectangles. Draw line 1 2. A C Example 2 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. 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). 3

4 Example 2 (Answer) 3) Oblique Planes Draw the isometric axes. Create the front isometric plane. Oblique Planes (cont.) Oblique Planes (cont.) Create the top isometric plane. Create the right side isometric plane. Locate the slot across the top plane. Step 6 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. 4) Angles Angles (cont.) Draw the isometric axes. Create the front, top and right isometric plane. Determine dimensions X and Y. Project both dimensions to create point Z (intersection point). 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. Multiview Projection 4

5 5) Irregular Curves Irregular Curves (cont.) Construct parallel lines (points 1 12). Project these lines into the top view (points 13 18). Draw horizontal lines). Create isometric box. Transfer dimension A to draw lines Draw isometric lines on the top face parallel to D line. Then, measure the horizontal spacing between each of the grid lines and transfer to isometric lines. Locate the intersection. Draw the curve using an irregular curve. Repeat the same step for the bottom plane to complete the isometric drawing. 6) Ellipses 6b) Approximate Four-Center Ellipse Construction 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. Construct an isometric equilateral parallelogram (sides equal) to the diameter of the circle. Find the midpoint of each side of the parallelogram. From that, draw a line to the closest endpoint of the opposite side. There are three methods to draw isometric ellipses; a) True ellipse construction. b) Approximate four-center ellipse construction. c) Isometric ellipse templates. Multiview Projection Approximate Four-Center Ellipse Construction (cont.) 7) Arcs Draw two small arcs with radius r (centers: A and B). Then, draw two large arcs with radius R (centers: C and D). Draw isometric box. Project arc center points A, B and C. Construct the isometric ellipse on the rear face. Add tangent lines. Multiview Drawing Construct isometric box. Draw the parallelogram with the sides equal to the diameter of the arc. Construct the bisector. Then, construct the isometric halfcircle. Project center points 1 and 2 to a distance equal to the thickness (T) of the object. 5

6 11/12/2015 Example 3 Example 3 (Answer) 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). 8) Screw Threads, Fillets and Rounds Screw Threads, Fillets and Rounds (cont.) Screw threads are represented by a series of equally spaced isometric ellipses whose major diameter is equal to the diameter of the screw. Fillets and rounds are drawn in such way to add more realism to the drawing. Marking of fillets and rounds in isometric drawings. 9) Isometric Grids An isometric grid is a grid paper set up using isometric axes with vertical and diagonal lines. The distance between grid points is normally 0.25 inch. 4) Oblique Drawings 1) Oblique Projection Theory Oblique projection The projectors/objects are parallel to each other but are not perpendicular to the projection plane. Typical oblique projection angles used are 30, 45 or 60 degrees from the horizontal. 6

7 Oblique Drawings (cont.) Oblique Drawings (cont.) Oblique Projection Theory (cont.) 2) Oblique Drawing Classifications Orthographic Projection The projectors are perpendicular to the projection plane. Orthographic Cavalier Oblique Drawn true length along the receding axis. Cabinet Oblique Drawn half the true length along the receding axis. General Oblique Drawn anywhere from greater than half length to less than full scale along the axis. Oblique Projection The projectors are never perpendicular to the projection plane. Oblique Oblique Drawings (cont.) Oblique Drawing Classifications (cont.) 3) Object Orientation Rules Oblique Drawings (cont.) First Rule Place complex features, such as arcs, holes or irregular surfaces, parallel to the frontal plane to avoid distortion and easy to be drawn. Second Rule The longest dimension should be parallel to the frontal plane. Cavalier oblique Cabinet oblique The cabinet oblique foreshorten the receding axis and gives a more realistic view. 5) Oblique Sketching 1) Box Technique Box Technique (cont.) Multiview Drawing Determine the best view for the front face. Create the construction box. Draw the receding axes at 45º. Draw the front view using the related dimensions. The other parts of the front view must be drawn at a distance P. Darken or trim the lines to complete the drawing. 7

8 2) Circular Features Circular Features (cont.) Multiview Drawing Determine the best view for the front face of the oblique drawing. Decide what type of oblique to draw. Draw the construction box. Draw the arc and the hole on the front face of the oblique drawing using the described dimensions. Project point A along a line at a 45º angle at 1 long (the depth dimension). Draw another arc using point B as center. Determine points of tangency. Circular Features (cont.) 3) Oblique Ellipse It is not always feasible to position an object such that all of its cylindrical features are parallel to the frontal plane. In oblique drawing, an alternate four-center ellipse method can be used to draw circles not in the frontal plane. Mark the notch dimensions on the front face. Mark the depth of the notch along the top left receding line. Draw the other arc and then the slot. Then, project point C back at 45º angle at 0.5 long. Draw the back part of the slot that is visible. Oblique Ellipse (cont.) Oblique Ellipse (cont.) On the surface that is not parallel to the frontal plane, locate the center of the circle and draw the center lines. Draw a construction circle that is equal to the diameter of the circle that is being constructed. From points A and C, construct lines that are perpendicular to center line BD. From points B and D, construct lines that are perpendicular to center line AC. Form the intersection of the perpendicular construction lines, draw four circular arcs using the radii marked. 8