MATSEC IM Engineering Drawing and Graphical Communication key terms

A method of representing a three-dimensional object by projecting its features onto two or more planes at right angles, producing separate views that together describe the object's true shape and size.

A projection convention in which the object sits between the observer and the plane, so the view seen from the front is placed below the plan and the left view appears on the right.

A projection convention in which the plane sits between the observer and the object, so the plan appears above the front view and the view from the left is placed on the left.

The principal orthographic view showing an object as seen from the front, normally chosen to reveal the most characteristic shape and the greatest amount of detail.

The orthographic view obtained by looking down on an object from above, drawn directly below the front elevation in first-angle layout and above it in third-angle layout.

A side orthographic view taken from the left or right of the object, used to show depth, widths and features that are hidden or foreshortened in the front view.

A short-dashed line type used in orthographic views to show edges and outlines that are concealed behind visible surfaces, drawn with evenly spaced dashes of consistent length.

A chain line of long and short dashes used to mark axes of symmetry, centres of circles and pitch circles on a drawing, extending slightly beyond the feature it identifies.

A continuous thick line that defines the visible edges and boundaries of the object in a view, forming the heaviest and most prominent linework on a technical drawing.

An agreed standard governing the type, thickness and application of lines on a drawing, such as continuous thick for outlines and continuous thin for dimension and projection lines.

A thin continuous line, terminated by arrowheads, that spans the distance being measured and carries the dimension value, normally placed outside the outline of the part.

A thin continuous line drawn from the feature being dimensioned to the dimension line, with a small gap at the feature and a short overshoot beyond the arrowhead.

A thin line, usually with an arrowhead or dot at one end, that connects a note, symbol or specification to the particular feature it describes on the drawing.

A dimension stating a straight-line distance such as length, width, height or centre distance, expressed in the drawing's stated unit and placed on a dimension line parallel to the measured direction.

A dimensioning method in which all dimensions are measured from one or more common reference surfaces or axes, reducing cumulative error and simplifying inspection of the finished part.

The total permissible variation in a dimension, expressed as the difference between upper and lower limits or as a single plus-or-minus value attached to the nominal size.

A system specifying the maximum and minimum permitted sizes of mating parts and the resulting clearance or interference, using hole-basis or shaft-basis designations such as H7 and g6.

A symbolic specification controlling form, orientation, location or runout of a feature, shown in a rectangular frame with a characteristic symbol, tolerance value and referenced datums.

A graphical symbol placed on a drawing to specify the required surface texture, typically giving a roughness value in micrometres and indicating whether material removal is permitted.

A pictorial drawing in which the three axes are spaced 120 degrees apart and all are foreshortened equally, so equal lengths along the axes appear equal on the drawing.

A pictorial representation built on three axes at 120 degrees using full true lengths along each axis rather than foreshortened lengths, making it slightly larger than a true isometric projection.

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

A family of parallel projections, including isometric, dimetric and trimetric, in which the object is tilted to show three faces and the axes are drawn at differing angles or scales.

Any three-dimensional-style illustration, such as isometric, oblique or perspective, used to convey the overall form of an object rather than precise orthographic measurements.

A pictorial assembly drawing in which components are drawn separated along a common axis, often with dashed alignment lines, to show how parts fit together and in what order.

A view produced by imagining the object cut by a plane and removing the nearer portion, with the cut surfaces shown hatched so internal features become visible outlines.

A heavy chain line with thick ends and arrows that shows where an object is imagined to be cut, the arrows indicating the direction in which the remaining part is viewed.

Evenly spaced thin parallel lines at a standard angle drawn across cut surfaces in a section view, with adjacent parts hatched in opposite directions or at different spacings.

A section view in which one half of the object is shown in section and the other half in outside view, useful for symmetrical parts where only one side needs internal detail.

An additional orthographic view projected onto a plane parallel to an inclined face, showing that face in true shape and size instead of the foreshortened form seen in the principal views.

The accurate unfolding of the surfaces of a hollow object onto a flat plane, producing a pattern from which the item can be cut and folded, as for ducts and sheet-metal work.

The accurate drawing of shapes such as bisectors, perpendiculars, tangents, polygons and ellipses using compass and straightedge methods rather than measurement alone.

The condition in which a line or curve touches a circle or arc at exactly one point, the common normal at that point passing through the centre of the arc.

Any of several drawing methods, such as the concentric-circle, trammel or four-centre approximation, used to plot an ellipse from its major and minor axes.

A rounded internal or external corner introduced on a drawing to reduce stress concentration or aid manufacture, specified by its radius and drawn tangent to the adjoining surfaces.

A drawing showing two or more components in their working relationship, identifying each part by number and giving overall dimensions rather than the dimensions of individual parts.

A tabulated list, usually placed above the title block, giving part numbers, descriptions, materials and quantities of every component shown in an assembly drawing.

The ruled panel, normally at the bottom right of a drawing sheet, recording the drawing title, number, scale, projection symbol, date, and the names of the drafter and checker.

The ratio between a drawn length and the real length it represents, stated on the drawing as full size, an enlargement such as 2:1, or a reduction such as 1:50.

The arranged organisation of a drawing sheet covering borders, margins, title block position, view placement, dimension distribution and notes so the information reads logically.

Any non-graphical information added to a drawing, including notes, symbols, material callouts, surface finish marks and references, used to specify requirements not conveyed by geometry alone.