TD6/1: ISOMETRIC PROJECTIONS AND AUXILIARY PROJECTION

Auxiliary Elevations and Auxiliary Plans

So far we have been able to draw four different views of the same block. In most engineering drawings these are sufficient but there are occasions when other views are necessary, perhaps to clarify a particular point. Figure 10.8 shows two examples where a view other than a FE or an EE is needed to show very important features of a flanged pipe and a bracket. These extra elevations are called auxiliary elevations (AE) or auxiliary plans (AP).

Figure 10.9 shows an AE and an AP of the shaped block. One is projected from the plan at 30 ° and the other from the FE at 45 ° . Projection lines are drawn at those angles and the heights, H and h, are marked off on one AE and the width W on the other. Remember that we are dealing with a solid block, not flat shapes on flat paper. Try to imagine the block as a solid object and these rather odd-shaped elevations will take on form and make sense.

Figure 10.10 shows two AP of a more complicated block. In this case the base is tilted and therefore cannot be used to measure the heights as before. This is overcome by drawing a datum line. The heights of all the corners are measured from this datum. Note that on the AP the datum is drawn at 90 ° to the projection lines.

If the outline contains circles or curves, the treatment is similar. Select some points on the curve and mark off their distances from some convenient datum. In Fig. 10.11 this gives dimensions a , b , c , d , e and f . The positions of these points are marked on the plan and they are projected onto the AE. The dimensions a to f are then marked off on the AE and the points joined together with a neat freehand curve.

It is worth stating again the difference between first and third angle projection, particularly if checked against the above examples. With first angle, if you look from one side of a view you draw what you see on the other side of that view. With third angle, if you look from one side of a view you draw what you see on the same side of that view. Shown below are some of the more common solid geometric solids drawn in orthographic projection.