MSCE Technical Drawing key terms

A straightedge with a fixed crossbar at one end that is held against the edge of the drawing board to guide horizontal lines and to support set squares for angled lines.

A triangular drawing tool with fixed angles, usually 45-45-90 or 30-60-90 degrees, used with a T-square or straightedge to draw lines at those angles and perpendiculars.

A thin template with a varied curved edge used to draw smooth irregular curves by joining plotted points in short matched segments rather than one continuous stroke.

A flat, true-surfaced working surface that holds the paper in position, often fitted with a parallel-motion straightedge or used with a T-square for horizontal alignment.

An instrument with two hinged legs, one holding a point and the other a pencil or pen, used to draw circles and arcs of a set radius about a centre.

A two-legged instrument with sharp points at both ends, used to transfer measurements, step off equal distances along a line, and mark points without drawing arcs.

A ruler marked with several proportional scales so that distances can be read directly at reduced or enlarged sizes, such as 1:50 or 1:100 on building drawings.

The hardness designation of a pencil lead, from soft 6B through medium HB to hard 9H, chosen so construction lines are light and final outlines are dark and reproducible.

The paper or film on which a drawing is produced, selected for size, weight, opacity and erasing quality, and usually laid out with a border, title block and zone references.

A ruled panel, normally at the lower right of the sheet, recording the drawing title, number, scale, projection symbol, date, revisions and the names of the drafter and checker.

To divide a line, angle or arc into two equal parts using compass arcs struck from its ends or sides, giving a midpoint or an angle bisector.

The line at right angles to a segment through its midpoint, found by striking equal arcs from both ends; every point on it is equidistant from the segment's endpoints.

A line or plane meeting another at exactly 90 degrees, constructed with a set square or by the semicircle method using arcs struck from a point on or off the line.

A straight line or arc that touches a curve at a single point without crossing it; constructions join arcs to lines or to other arcs by locating the tangent point and centre.

A light, thin line drawn to locate centres, tangent points and projected features; it guides the geometry but is not part of the finished outline and may be left unerased or erased.

A closed curve traced by a point whose distances from two fixed foci sum to a constant; drawn by the concentric-circle, trammel or approximate four-centre method.

A plane figure with all sides and interior angles equal, constructed inside or on a given circle by dividing the circle into equal parts, for example a hexagon by stepping the radius.

A projection system in which the object sits between the observer and the plane, so the view seen from the front is placed below the front view in the layout.

A projection system in which the plane sits between the observer and the object, so each view appears on the side of the front view from which it is seen.

The principal orthographic view chosen to show the object's most characteristic shape and length; other views are projected from it and aligned with it.

The view obtained by looking down on an object or building from above, projected below the front view in first angle and above it in third angle.

The truncated cone symbol placed in or near the title block, showing the arrangement of front and side views, which identifies whether first- or third-angle projection is used.

A short-dashed line showing an edge or outline that is concealed in a particular view; dashes are evenly spaced and meet at corners to keep the outline readable.

An imaginary plane that passes through an object to define where it is sliced; its trace is shown on other views as a heavy chain line with arrows giving the viewing direction.

A view showing the cut face and visible edges behind the cutting plane, drawn so internal features appear as solid outlines rather than hidden detail lines.

Thin, evenly spaced parallel lines at about 45 degrees filling cut surfaces in a section; adjacent parts are hatched at different angles or spacings to distinguish them.

A heavy line type used for the trace of a cutting plane, commonly long dashes with short gaps ending in arrows that point in the direction of sight.

A pictorial drawing on three axes spaced 120 degrees apart, with vertical edges true and the two receding axes at 30 degrees, giving equal foreshortening along each axis.

A pictorial view with the front face drawn true shape and parallel lines receding at an angle, usually 45 degrees, at full or half scale to show depth.

The point on the horizon where parallel receding lines appear to converge in a perspective drawing; one or two points give one- or two-point perspective.

The horizontal line in a perspective drawing at the observer's eye level; all vanishing points lie on it and object height relative to it fixes the viewpoint.

A thin line, usually with arrowheads at each end, drawn between extension lines to show the extent of a dimension; the value is placed above or in a break in it.

A thin line projecting from an object's feature to carry a dimension line clear of the outline, with a small gap at the feature and a short overshoot beyond the arrowhead.

A thin line ending in an arrowhead on a feature and running to a note or dimension, usually inclined and with a short horizontal shoulder where text begins.

The permitted maximum and minimum sizes of mating parts, chosen from standard hole-basis or shaft-basis systems so that clearance, transition or interference results as intended.

The total permissible variation in a dimension, being the difference between upper and lower limits; it may be stated as a value or as plus and minus deviations.

A theoretically exact point, line or surface from which dimensions or geometric tolerances are measured, identified on the drawing by a datum feature symbol.

A tick-shaped symbol on a drawing that specifies the required surface texture, carrying a roughness value such as Ra in micrometres and optional machining process notes.

A scaled plan of a plot showing the building outline, boundaries, access, levels and services, used to set the structure in relation to its surroundings.

A horizontal section through a building at about one metre above floor level, showing walls, openings, stairs, fixtures and room names with dimensions.

An orthographic view of the external face of a building or component, showing heights, levels and finishes but no depth, projected from the plan.

A pictorial drawing in which the parts of an assembly are separated along their assembly axes, with thin chain lines showing how they fit together.

A table, often above the title block, listing each part in an assembly by item number, description, material, quantity and drawing or standard reference.

A drawing showing several parts in their working relationship, giving overall dimensions, part references and fitting information rather than the detail needed to make each part.

A drawing made without instruments, using light construction lines and proportional judgment to record shape and size quickly and clearly.

Standard upright or inclined capital lettering used for notes and dimensions, drawn with consistent height, stroke and spacing so it stays legible when reduced.

A named CAD organisational level holding objects that share properties such as colour and line type, which can be shown, frozen or locked independently.

The CAD environment where geometry is drawn at full size in three dimensions or in plan, separate from the sheet layout used for plotting.

A CAD setting that makes the cursor jump to precise points on existing geometry, such as endpoints, midpoints, centres and intersections, instead of free positions.