Orthogonal drawings show a three dimensional object as a series of two dimensional drawings. The multiview drawings should be read simultaneously.
How Many Views?
Simple forms based on cubes, cylinders, cones or pyramids may need only two views to adequately describe their form. More complicated forms may need up to six views – top and front, left and right sides, rear and bottom. The answer is: The minimum necessary to ensure no misunderstanding and that details of the object are clearly shown.
Which is the Front View?
In third angle projection, the top view shows the width and depth of an object, the front view shows the height and width, and the side views will show the height and depth.
How do you decide if no front view is shown?
You need to consider which view is most descriptive of the overall form. In the example below, it would be correct to nominate view b s the Front View. Therefore, the other views that will be drawing of this object are the Left Side View (view a) and the Top View
DRAWING HIDDEN EDGES
Hidden edges are edges that exist in the ‘real’ form but are not visible in an orthogonal or 3D drawing. Hidden edges are shown with a broken line. Broken lines indicating a hidden edge should be drawn with consistency, e.g. line thickness, dash and spacing. Lengths of dashes and spaces may vary depending on the length of line and the size of the drawing. Dashed lines should start and end in dashes in contact with the visible or hidden lines.
THIRD ANGLE ORTHOGONAL
Third angle orthogonal is a layout system which identifies each view in relation to the front view of the object and is indicated by a symbol. Put simply, the top view is placed directly above the front view, the left side view is placed directly on the left hand side of the front view, and the right side view is placed directly on the right hand side of the front view. If more views are required, then you simply continue the logical placement of each view – bottom view below the front view and rear view placed to the right of the right side view.
THIRD ANGLE ORTHOGONAL PROJECTION SYMBOL
The symbol is an orthogonal drawing of a trapezoid. The measurements for the symbol are easy to remember, 16mm and 8mm. Note that the object lines are thicker than the lines indicating the centre of the trapezoid and that the horizontal center line is broken (chain line). (Note that the dimension lines and measurements shown here are NOT part of the symbol.)
The symbol should be placed neatly in the title block of your drawing, or if showing other views, near the orthogonal drawings.