7 - Engineering drawing and welding symbols

Summary

Engineering drawing

The principal method usually adopted in the making of machine drawings is known as orthographic projection.

Suppose the part under construction is shown in Fig 7.1a. This ‘picture’ is known as an isometric view. It is of small use to the engineer, since it is difficult to include on it all the details and dimensions required, especially those on the back of the picture, which is hidden.

Imagine that around the object a box is constructed (O being the corner farthest from the observer) having the sides Ox, Oy, Oz all at right angles to each other. The plane or surface of the box bounded by Ox and Oy is the vertical plane, indicated by VP; that bounded by Oy, Oz is the side vertical plane, SVP, and that bounded by Ox and Oz, the horizontal plane, HP, these three planes being the three sides of the box farthest from the observer. Lines are projected, as shown, onto these planes from the object under consideration, and the view obtained when looking at the object in the direction of the arrow A. The end elevation is the view obtained by projection on to the side vertical plane, while the plan is the view obtained by projection on to the horizontal plane. The arrow B shows the direction in which the object is viewed for the side elevation and C the direction for the plan.