Technical Drawing: Isometric, Conical Perspective and Scale

Isometric Drawing Steps

1. Axis Construction: The three axes are drawn using set squares. To draw the X and Y axes, the 30-60-90º set square’s 30º angle is used.
2. Box Creation: The object’s measurements are marked on the axes, corresponding to the object’s three edges. Using set squares, parallel lines are drawn to create the bounding box for the figure.
3. Detailing: Measurements of the different parts of the views are marked. Sketch lines parallel to the edges of the box lightly, as some will be erased later.
4. Finalizing: Visible edges are drawn using darker lines, and construction lines are erased.

Conical Perspective

Conical perspective is based on the optical effects that occur in an object’s measurements as it moves farther from the observer. The point towards which lines converge is called the vanishing point. The appearance of an object in conical perspective depends strongly upon the location of this vanishing point.

Steps for Conical Perspective

1. Draw the front face of the object and place the vanishing point (VP) based on the desired perspective (e.g., from above or from the center).
2. Draw very light lines from the vanishing point to the vertices of the face you have drawn.
3. Add the contours of the object by drawing lines parallel to the front edges. Finally, trace the contours using darker lines.

Scale in Technical Drawing

Scale is the ratio between the dimensions in a drawing and the actual measurements of the object being represented.

Types of Scale

• Reduced scale: The measurements in the drawing are smaller than the object’s actual dimensions.
• Actual scale (Natural scale): Used when the object’s dimensions allow its actual measurements to be represented. It is expressed as S = 1:1.
• Enlarged scale: The measurements in the drawing are larger than the object’s actual dimensions. This is used to represent small objects.

Object Annotation

Annotating an object consists of indicating all of its actual dimensions so that they can be accurately interpreted.