Auxiliary Views

Primary Auxiliary Views
Primary auxiliary view sometimes called helper view is used to clearly and completely explain the shape of the object. Most objects have sloping or inclined surfaces that are not perpendicular to the plane of projection. Typical orthographic view represents these surfaces as distorted and does not show their true shape. When a sloping surface has an important feature that should be shown without distortion, an auxiliary view is used.
Since auxiliary view drawing usually shows only the true-shape features and detail of the inclined surface, only partial auxiliary view is necessary to be drawn.
How to make auxiliary view
The regular orthographic view has a line that represents the edge of the inclined surface. The auxiliary view is projected, at right angles, from this edge line and drawn parallel to it.

fig.1

Figure 2 shows the process of making an auxiliary view of a symmetrical object.
1. The center plane (AB) is drawn parallel to the inclined surface and it is used as representation of the reference plane. This plane appears as a center line (A’B’) on the top view.
2. The Points of intersection between the inclined surface and the vertical lines on the top view are numbered, and than transferred to the edge view of the inclined surface on the front view.
3. In the top view distances C and D are found from the numbered points to the center line, and then transferred on the matching construction lines, measuring them off on either side of the line AB.
4. Apply this step to other points.
5. Connect and number these points. This will result with a front auxiliary view of the inclined surface.

Fig.2

Multi Auxiliary View Drawings
Some objects are more complex and may have more than one surface not at right angles to the plane of projection. These objects, may required auxiliary view for each such surface. This kind of drawing is referred to as the multi auxiliary view drawing.

Representation of circular features in auxiliary view drawings
Circular features in auxiliary projection appear elliptical, not circular. The most commonly used method to draw the true shape of the curved surface is the plotting of a series of points on the line. The more points are plotted on the line, the accuracy of the curve or circular feature is better. The easiest way to explain this method of auxiliary projection is the projection of a truncated cylinder. This shape seen in the auxiliary projection is an ellipse, as shown in figure 3.

Fig.3

The best approach to projection of a circular shape is by plotting lines of intersection.
1. A center line (AB) of the auxiliary view is drawn parallel to the edge line.
2. The parameter of the circle in the top view needs to be divided into equal slices or equally spaced points. Our example is divided in 24 equally spaced points, 15° apart. The circumference of the circle (360°) is divided in 24 equal spaces, 360°/24=15°.
3. These points are then projected down to the edge line on the front view, then at right angles toward and past the center line of the auxiliary view.
4. The widths between the center line and individual points taken from the top view are transferred to the auxiliary view. This is shown as lengths C and D for points 5 and 23 in Fig. 3.
5. When all the widths have been transferred from the top view to the auxiliary view, the resulting points of intersection are connected to give the preferred elliptical shape.

Some complex objects can be only described by using secondary auxiliary view. The procedures for projecting and drawing a secondary auxiliary view are the same as those for a primary auxiliary view. Because of the complexity of their features (usually inclined or sloping toward the plane of projection), some objects require the drawing of partial front and top views from which primary and secondary auxiliary views can then be drawn. The auxiliary views can then be used for finishing the top and front views.

Written by P.A