MATSEC SEC Graphical Communication key terms

A method of representing a three-dimensional object by projecting its features at right angles onto two or more flat planes, producing separate views that show true shape and size where the surfaces are parallel to the plane.

A projection arrangement in which the object sits between the observer and the projection plane, so the view seen from the front is placed above the plan on the drawing sheet.

A projection arrangement in which the projection plane lies between the observer and the object, so the plan is placed above the front elevation on the drawing sheet.

The orthographic view obtained by looking at the front of an object; it usually shows the most descriptive face and is drawn first, fixing the height and width of the object.

The orthographic view seen when looking down on an object from above, drawn below the front elevation in first-angle layout and showing the width and depth of the object.

A side view of an object, projected from the front elevation, showing its depth and height; left and right end elevations are placed on opposite sides in third-angle work.

A short dashed line used in a view to show an edge or feature that is present but cannot be seen from that viewing direction, such as a hole inside a block.

A chain line of long and short dashes drawn through the centre of symmetrical features such as circles, cylinders and holes to mark their axis and help locate them in each view.

An additional orthographic view projected onto a plane that is not one of the three principal planes, used to show the true shape of a sloping or inclined face.

A pictorial method in which the three axes are set 120 degrees apart on the paper, so vertical edges stay vertical and the two horizontal directions rise at 30 degrees to the horizontal.

A pictorial drawing built on isometric axes in which all dimensions are measured true length along the axes rather than reduced by the isometric scale, making it slightly larger than true isometric projection.

The three lines, one vertical and two at 30 degrees to the horizontal, from which an isometric drawing is constructed and along which lengths, widths and heights are measured.

A reduced scale of about 0.816 of true length used to measure along isometric axes when drawing a true isometric projection; most school drawings ignore it and use full sizes.

A line in an isometric drawing that does not run parallel to one of the three isometric axes, such as a diagonal or sloping edge, so its true length cannot be read directly and must be found by coordinates.

A pictorial method in which the front face of the object is drawn true shape parallel to the picture plane, while receding edges are drawn at an angle, usually 45 degrees, to show depth.

A form of oblique projection in which receding edges are drawn at full true length, giving an exaggerated sense of depth; the front face remains undistorted.

A form of oblique projection in which receding edges are drawn at half their true length to reduce distortion; it gives a more natural appearance than cavalier projection.

The path traced by a point that moves according to a given rule, such as a point always a fixed distance from a fixed point, which produces a circle.

The line that cuts a straight line segment exactly in half at right angles; every point on it is the same distance from the two endpoints of the segment.

A line that divides an angle into two equal parts; any point on it is equidistant from the two arms of the angle.

A straight line that touches a curve at a single point without crossing it; at that point the tangent is at right angles to the radius drawn from the centre of a circle.

A line drawn at right angles to a tangent at the point of contact; in engineering drawing it is often needed to locate centres when drawing curves such as ellipses.

A closed curve shaped like a flattened circle, traced by a point whose total distance from two fixed points called foci stays constant; drawn in plane geometry by methods such as auxiliary circles.

A closed plane figure with all sides equal and all interior angles equal, such as a pentagon or hexagon, usually constructed inside or outside a given circle.

The largest circle that fits inside a polygon and touches all its sides, with its centre found where the angle bisectors meet.

An imaginary flat surface used to slice through a solid so that a section view can be drawn; its position is indicated in another view by a chain line with arrows showing the viewing direction.

A view that shows the interior of a solid as it would appear if cut by a cutting plane, with the cut surfaces filled with evenly spaced hatching lines.

The actual shape and size of a face or section, seen only when the viewing direction is at right angles to that surface; it is found by projection from an auxiliary plane.

A solid with two identical parallel end faces called bases and flat rectangular side faces joining them; a right prism has its axis at right angles to its base.

A solid with a polygon as its base and triangular faces that meet at a single point called the apex; the perpendicular height is the shortest distance from apex to base.

The part of a solid, such as a cone or pyramid, that remains after the top has been cut off by a plane parallel to the base.

The flat pattern obtained by unfolding the surfaces of a solid onto a single plane, used to mark out sheet metal or card before folding and joining.

A method of developing solids such as prisms and cylinders whose surfaces are made of parallel straight elements; the base is stretched out and the heights transferred from the elevation.

A method of developing solids such as pyramids and cones whose surfaces taper to an apex; true lengths of sloping edges are found and swung as radii from the apex.

Evenly spaced thin parallel lines at about 45 degrees used to shade the cut surfaces in a section view; adjacent parts are hatched in opposite directions to distinguish them.

Drawing without instruments, using light construction lines and judgement of proportion to record or communicate an idea quickly; lines are usually kept single-stroke and confident.

A panel, usually at the bottom right of a drawing sheet, giving information such as the title, drawing number, scale, date, material and the name of the draughtsperson.

A thin line, usually with arrowheads at both ends, that carries a measurement; it is drawn parallel to the feature and kept clear of the outline, with extension lines marking its limits.

The ratio between a drawn length and the real length it represents, written for example as 1:20 for a reduction or 2:1 for an enlargement.

A very light thin line drawn first to locate centres, heights or key points; it is not part of the finished drawing and may be left visible or erased.