MATSEC AM Graphical Communication cheat sheet

Standard drawing sheet sizes follow the ISO A series: A0 = 841 × 1189 mm, and each subsequent size halves the longer side (A1 = 594 × 841 mm, A2 = 420 × 594 mm, A3 = 297 × 420 mm, A4 = 210 × 297 mm).

Scale is expressed as drawn length : real length; a scale of 1:50 means 1 mm on paper represents 50 mm (0.05 m) in reality, so a 3 m wall is drawn 60 mm long.

Line hierarchy: continuous thick lines for visible outlines, continuous thin lines for dimension and projection lines, dashed lines for hidden edges, and chain lines for centre lines and cutting planes.

First-angle projection (the ISO/European convention used in Malta): the object sits between observer and plane, so the plan is placed below the front elevation and the left view appears on the right.

Third-angle projection places the plane between observer and object: the plan sits above the front elevation and the view seen from the left is drawn on the left.

A regular polygon of n sides has exterior angle 360°/n and interior angle (n − 2) × 180°/n; for a hexagon these are 60° and 120° respectively.

To construct a regular polygon on a given side, use the exterior angle at each end of the side, or divide a semicircle on the side into n equal parts and radiate to the second division point.

Dimensioning rules: give each dimension once only, place it outside the outline, use arrowheads at both ends, and state the unit once in the title block rather than on every dimension.

An ellipse can be drawn by the concentric-circle method (divide a circle pair into equal angular divisions and project) or the trammel/auxiliary-circle method; the major axis is the longest diameter, the minor axis the shortest.

A parabola is the locus of points equidistant from a fixed point (focus) and a fixed line (directrix); every point on it satisfies distance-to-focus = distance-to-directrix.

A hyperbola is the locus where the difference of distances to two foci is constant; a rectangular hyperbola has asymptotes at right angles.

To find the true shape of an inclined face, project perpendicular to the edge view of that face; the resulting auxiliary view shows the face undistorted.

A point on an inclined line divides it in the same ratio in every view, so a proportion established in the plan transfers directly to the elevation.

An involute is generated by unwinding a taut string from a polygon or circle; it is used to profile gear teeth, and its normal at any point is tangent to the base circle.

A helix is the path of a point moving at constant speed around a cylinder while advancing at constant speed along its axis; one full turn advances by the lead.

Section views show internal detail: hatch adjacent parts in opposite directions at 45°, never hatch shafts, bolts, nuts or standard fasteners cut longitudinally, and label the cutting plane A–A.

Tolerances and fits use ISO limits: a hole basis is written H for the hole (lower deviation zero) and a lowercase letter for the shaft, e.g. 20 H7/g6 denotes a close running fit.