Orthographic Projection and Multi-View Drawing
This domain tests whether you can convert a three-dimensional object into a correctly related set of two-dimensional views - front elevation, plan and end elevation - drawn to a stated scale, properly aligned and correctly line-weighted.
Layout: first-angle projection
MATSEC work follows first-angle projection (ISO 128 / BS 8888). The object sits between the observer and the plane of projection, so the plan is drawn below the front elevation, and the end elevation seen from the left is placed on the right. Views are tied together by projectors: heights travel from the elevation to the end elevation, widths from the elevation to the plan, and depths from the plan across to the end elevation through a 45° mitre line.
Choosing and relating views
Select as front elevation the view showing the most characteristic outline and producing the fewest hidden lines. Never guess a dimension that can be projected; if two views disagree, the drawing is wrong, not the object.
Line conventions
Visible edges: continuous thick. Hidden edges: short dashes of even length and spacing. Centre lines: long–short chain, extended slightly beyond the outline. Projection and construction lines: continuous thin, left in place.
Worked example
A block 70 mm long × 40 mm deep × 30 mm high has a 20 mm square hole passing vertically through its centre. In the front elevation the hole appears as two hidden vertical lines 20 mm apart, symmetrical about the vertical centre line of the 70 mm length. In the plan it is a 20 mm square sitting on the centre lines. No height is dimensioned for the hole: the plan carries the note '20 □ THRU', and the elevation simply shows hidden lines from top face to bottom face.
Traps that cost marks
Putting the plan above the elevation (third-angle habit); omitting hidden lines; broken or uneven dashes; drawing the mitre line at the wrong corner; and dimensioning on the plan a height that only the elevation can give.