Technical Drawing, Graphics and Communication
Technical Drawing, Graphics and Communication tests reading and producing orthographic and pictorial drawings, line conventions and dimensioning.
Views and projection
First-angle projection places the top view below the front view and the side view on the opposite side. Third-angle projection places the top view above the front view and the side view on the side from which it is viewed. Check the projection symbol. Align views, and show hidden features with dashed lines.
Line types and dimensioning
Continuous thick lines are outlines; thin continuous lines are dimension and projection lines; dashed lines are hidden; chain lines are centre lines. Dimension in millimetres without the unit symbol. Give each dimension once, place it outside the outline where possible, and dimension to visible edges rather than hidden ones.
Pictorial drawings
Isometric axes are 30 degrees to the horizontal, with true lengths drawn along them. Oblique drawing uses a true-shape front face with receding lines at 45 degrees. Use pictorial drawings for communication, not for manufacturing dimensions.
Worked example
A rectangular block 60 mm x 40 mm x 20 mm has a 10 mm diameter hole through its thickness. Draw the front view as a 60 x 20 rectangle, the top view as 60 x 40 below it in first angle, and show the hole as two hidden lines in the front view and a circle in the top view. Dimension overall length, width and height, and the hole diameter once. Reasoning: the hole is not visible from the front, so hidden lines are correct, and repeating the diameter on both views is unnecessary.
Traps
Mixing first- and third-angle views, omitting hidden lines, dimensioning to a hidden line, leaving gaps at corners, and using a scale without stating it all lose marks. Poor line quality and unreadable lettering also cost marks.