- Understanding Solid Objects
- Understanding Sketching Techniques
- 3.1 Technique of Lines
- 3.2 Sketching Straight Lines
- 3.3 Sketching Circles, Arcs, and Ellipses
- 3.4 Maintaining Proportions
- 3.5 One-View Drawings
- 3.6 Pictorial Sketching
- 3.7 Projection Methods
- 3.8 Axonometric Projection
- 3.9 Isometric Projection
- 3.10 Isometric Drawings
- 3.11 Making an Isometric Drawing
- 3.12 Offset Location Measurements
- 3.13 Hidden Lines and Centerlines
- 3.14 Angles in Isometric
- 3.15 Irregular Objects
- 3.16 Curves in Isometric
- 3.17 True Ellipses in Isometric
- 3.18 Orienting Ellipses in Isometric Drawings
- 3.19 Drawing Isometric Cylinders
- 3.20 Screw Threads in Isometric
- 3.21 Arcs in Isometric
- 3.22 spheres in Isometric
- 3.23 Oblique Sketches
- 3.24 Length of Receding Lines
- 3.25 Choice of Position in Oblique Drawings
- 3.26 Ellipses for Oblique Drawings
- 3.27 Angles in Oblique Projection
- 3.28 Sketching Assemblies
- 3.29 Sketching Perspectives
- 3.30 Curves and Circles in Perspective
- 3.31 Shading
- 3.32 Computer Graphics
- 3.33 Drawing on Drawing
- Key Words
- Chapter Summary
- Worksheets
- Review Questions
- Sketching Exercises
This chapter is from the book
This chapter is from the book
This chapter is from the book
3.17 True Ellipses in Isometric
If a circle lies in a plane that is not parallel to the plane of projection, the circle projects as an ellipse. The ellipse can be constructed using offset measurements.
STEP by STEP: DRAWING AN ISOMETRIC ELLIPSE BY OFFSET MEASUREMENTS
Random-Line Method
Draw parallel lines spaced at random across the circle.
Transfer these lines to the isometric drawing. Where the hole exits the bottom of the block, locate points by measuring down a distance equal to the height d of the block from each of the upper points. Draw the ellipse, part of which will be hidden, through these points. Darken the final drawing lines.
Eight-Point Method
Enclose the given circle in a square, and draw diagonals. Draw another square through the points of intersection of the diagonals and the circle as shown.
Draw this same construction in the isometric, transferring distances a and b. (If more points are desired, add random parallel lines, as above.) The centerlines in the isometric are the conjugate diameters of the ellipse. The 45° diagonals coincide with the major and minor axes of the ellipse. The minor axis is equal in length to the sides of the inscribed square.
When more accuracy is required, divide the circle into 12 equal parts, as shown.
Nonisometric Lines
If a curve lies in a nonisometric plane, not all offset measurements can be applied directly. The elliptical face shown in the auxiliary view lies in an inclined nonisometric plane.
Draw lines in the orthographic view to locate points.
Enclose the cylinder in a construction box and draw the box in the isometric drawing. Draw the base using offset measurements, and construct the inclined ellipse by locating points and drawing the final curve through them.
Measure distances parallel to an isometric axis (a, b, etc.) in the isometric drawing on each side of the centerline X–X. Project those not parallel to any isometric axis (e, f, etc.) to the front view and down to the base, then measure along the lower edge of the construction box, as shown.
Darken final lines.
