Pictorial Drawings

Axonometric Projections

Step by Step:Isometric Sketching

Isometric Projection vs. Sketch

Isometric projections are foreshortened because the object is tipped with respect to the viewing plane. Isometric sketches are not usually foreshortened because they still appear proportionate when showing the dimensions full size along isometric axis lines. It is easier just to sketch the full dimension.

Locating Features

To locate a feature such as the upper block, make measurements from an existing corner as shown here.

Inclined Surfaces in Isometric

Inclined surfaces can not be measured along inclined lines in an isometric sketch. To locate inclined surfaces you must make measurements along the isometric axis lines.

Circles in Isometric

• Circles appear as ellispses when drawn in an isometric sketch.

• To sketch an isometric circle, locate the center and then sketch the box that would enclose the circular shape. Draw the ellispse tangent to the lines of the box.

Arcs in Isometric Sketches

Arcs are usually sketched by locating their centers and then boxing in the enclosing parallelogram. Sketch the arc tangent to the enclosing box, which is drawn along isometric lines.

Hidden LinesHidden lines are not usually shown in isometric sketches unless they are needed to show a feature that would be unclear.

Usually the orientation for the isometric drawing should be chosen so that hidden lines aren’t needed.

Holes are assumed to go completely through the object unless their depth is indicated with a note or with hidden lines.

Exploded Isometric Assembly

Isometric drawings are frequently used to show how parts assemble as in this automobile power module.

Oblique Pictorials

The advantage of oblique pictorials like these over isometric pictorials is that circular shapes parallel to the view are shown true shape, making them easy to sketch.

Oblique pictorials are not as realistic as isometric views because the depth can appear very distorted. Oblique views cannot usually be generated directly from a 3D model using CAD. It is primarily a sketching technique.

Unnatural Appearance ofOblique Drawing

Oblique drawings of objects having a lot of depth can appear very unnatural due to the lack of foreshortening.

Perspective Drawings

• Perspective drawings produce the view that is most realistic. A perspective drawing shows a view like a picture taken with a camera

• There are three main types of perspective drawings depending on how many vanishing points are used.

• These are called one-point, two-point, and three-point perspectives.

One Point Perspective

Orient the object so that a principal face is parallel to the viewing plane (or in the picture plane.) The other principal face is perpendicular to the viewing plane and its lines converge to a single vanishing point.

Terminology

One-point Perspective Sketching

Sketch front surface of object and locate vanishing point.

1.

Sketch receding lines

Sketch receding lines from intersections and points of tangency on front surface to vanishing point.

2.

Estimate the depth of the object you will show and block in the back surface between the receding lines.

3.

Shading Techniques