MATSEC AM Graphical Communication flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

ISO A0 sheet size

841 mm × 1189 mm, with an area of almost exactly one square metre. Every smaller A size is made by halving the area, keeping the same aspect ratio.

Scale 1:50 meaning

One unit drawn represents fifty real units, so a 4 m wall is drawn 80 mm long. Enlargement scales such as 5:1 are written with the larger number first.

First-angle projection layout

The object lies between the observer and the plane, so the view from above (plan) is placed below the front elevation, and the left-hand side appears on the right.

Third-angle projection layout

The plane sits between observer and object, so the plan appears above the front elevation and the view from the left is drawn on the left side.

Hidden detail line

A dashed line of short evenly spaced dashes used for edges not visible in that view. Dashes should meet at corners and not continue across dimension lines.

Centre line convention

A chain line of long dashes alternating with short dashes, drawn through axes of symmetry, circles and bolt circles, extending slightly beyond the outline of the feature.

Interior angle formula

For a regular polygon with n sides, each interior angle equals (n − 2) × 180° ÷ n. A regular pentagon therefore has interior angles of 108°.

Exterior angle of polygon

Each exterior angle of a regular n-sided polygon is 360° ÷ n. Turning through this angle at every vertex returns the pen to the starting direction.

Constructing a regular hexagon

Step off the compass radius around a circle six times, since the chord of a hexagon equals its circumradius. Join alternate points for an equilateral triangle.

Bisecting an angle

Draw an arc from the vertex cutting both arms, then equal arcs from those two points. The line from the vertex through their intersection bisects the angle.

Perpendicular bisector of a line

With equal radii greater than half the line, draw arcs from each endpoint on both sides. The line joining the two arc intersections is the perpendicular bisector.

Ellipse major and minor axes

The major axis is the longest diameter through the centre; the minor axis is the shortest, perpendicular to it. Foci lie on the major axis, equidistant from the centre.

Trammel method for ellipse

Mark half the major axis and half the minor axis on a straight strip. Sliding the strip so the marks follow the axes traces points on the ellipse.

Parabola focus-directrix property

Every point on a parabola is the same distance from the focus as from the directrix. The vertex lies midway between focus and directrix.

Hyperbola definition

The locus of points for which the absolute difference of distances to two fixed foci is constant. The curve has two separate branches and two asymptotes.

Rectangular hyperbola asymptotes

A hyperbola whose asymptotes meet at 90°. It is the graph of y = k/x and is used in graphical work to interpolate between non-linear data points.

Involute of a circle

The curve traced by the end of a taut string unwound from the circle. Used to profile gear teeth; the normal at any point touches the base circle.

Helix lead and pitch

A helix advances one lead per full revolution around the cylinder. Pitch is the axial distance between corresponding points on successive turns.

Auxiliary view purpose

A view projected perpendicular to an inclined face so that face appears in true shape and size. Project lines are drawn at right angles to the edge view.

True length of inclined line

An inclined line appears foreshortened in plan and elevation. Its true length is found by constructing a right triangle whose height is the difference in levels.

Dimension line rules

Dimension lines are thin continuous lines with arrowheads at both ends, placed outside the outline. Each dimension is given once, on the view that shows the feature clearly.

Leader line for a circle

A thin line with an arrow touching the circumference, drawn radially and ending in a short horizontal shoulder on which the diameter or radius is written.

Diameter and radius symbols

The symbol Ø precedes a diameter value and R precedes a radius value. A full circle is dimensioned by diameter, an arc by radius.

Section hatching convention

Cut surfaces are hatched with thin lines at 45°. Adjacent parts are hatched in opposite directions, and standard fasteners are not hatched when cut lengthwise.

Cutting plane line

A chain line thickened at the ends and at changes of direction, with arrows showing the viewing direction and capital letters naming the section, such as A–A.

ISO limit system hole basis

The hole is designated H, meaning its lower deviation is zero. The shaft letter sets the fit, so H7/g6 is a close running fit and H7/s6 an interference fit.

Title block contents

A ruled block in the bottom right corner giving drawing title, number, scale, projection symbol, units, material, date, and the names of draughtsman and checker.

Projection symbol on drawing

A truncated cone with its circle and side view; the arrangement of circle and trapezium indicates first- or third-angle projection, removing any ambiguity from the layout.

Freehand sketching technique

Block in overall proportions with light construction lines, then darken the final outline. Keep lines single-stroke and rotate the paper rather than the wrist for long curves.

Isometric axes and angles

Three axes at 120° to each other, with vertical edges drawn vertically and the two receding axes at 30° to the horizontal. All measurements are drawn to full scale.

Oblique projection cavalier

The front face is drawn true shape and size, with receding edges at 45°. Cavalier projects receding edges full length; cabinet halves them to reduce distortion.

One-point perspective

Parallel edges facing the viewer stay parallel and true, while edges receding to depth converge at a single vanishing point placed on the horizon line.

Tangent construction

Where a line touches a circle, the radius drawn to the point of contact is perpendicular to the tangent. This rule locates tangency points in blending arcs.