Symbol Of First Angle Projection In Engineering Drawing

First angle projection

Assume that a small block is made 35 mm x 30 mm x 20 mm and that two of the corners are cut away as shown below in three stages.

Figure 4.2 illustrates a pictorial view of the block and this has been arranged in an arbitrary way because none of the faces are more important than the others. In order to describe the orthographic views we need to select a principal view and in this case we have chosen the view in direction of arrow A to be the view from the front.

The five arrows point to different surfaces of the block and five views will result. The arrows themselves are positioned square to the surfaces, that is at 90° to the surfaces and they are also at 90°, or multiples of 90° to each other. The views are designated as follows: View in direction A is the view from the front, View in direction B is the view from the left, View in direction C is the view from the right, View in direction D is the view from above, View in direction E is the view from below.

In first angle projection the views in the directions of arrows B, C, D and E are arranged with reference to the front view as follows: The view from B is placed on the right, The view from C is placed on the left, The view from D is placed underneath, The view from E is placed above.

The experienced draughtsman will commit the above rules to memory. It is customary to state the projection used on orthographic drawings to remove all doubt, or use the distinguishing symbol which is shown on the arrangement in Fig. 4.3.

: View E

View C

View A

View B

View D

View B

View A

View C

View A

View E

Projection symbol

View D

Projection symbol

Fig. 4.3 First angle projection arrangement. Dotted lines indicate hidden edges and corners

View E

Projection symbol Fig. 4.4 Third angle projection arrangement

Continue reading here: Third angle projection

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