UPMSP Intermediate Technical Drawing cheat sheet

Standard sheet sizes (ISO A series) follow halving: A0 = 841 × 1189 mm; A1 = 594 × 841; A2 = 420 × 594; A3 = 297 × 420; A4 = 210 × 297 mm.

A1, A2, A3 and A4 drawing boards are sized so the sheet fits with a filing margin; the title block sits at the bottom-right corner of the sheet.

Pencil grades: 9H hardest to 9B softest; H and 2H for construction/layout lines, HB for lettering and freehand, 2B–4B for soft sketching and shading.

Set squares used are 45°–45°–90° and 30°–60°–90°; combined with a T-square they give multiples of 15° (15°, 30°, 45°, 60°, 75°, 90°).

A T-square stock is held against the board's working edge; the blade gives horizontal lines only when the board edge is true.

Compass is used for circles and arcs; dividers transfer and step off equal distances along a line or arc.

French curve (irregular curve) draws smooth non-circular curves through plotted points; a minimum of three points is needed to align it.

Standard line thickness ratio is approximately 1 : 0.7 : 0.5 (thick : medium : thin); visible outlines are thick, construction and dimension lines thin.

IS lettering convention: single-stroke italic (sloping) capital letters at 75° to the horizontal; height-to-width ratio about 7 : 4, stroke spacing about 1/7 of letter height.

Standard lettering heights (mm): 2.5, 3.5, 5, 7, 10, 14, 20; height h and line spacing are chosen so lowercase x-height is about 0.7h.

Dimension line carries the value and is drawn thin, parallel to the measured edge, with arrowheads touching both extension lines.

Extension (projection) lines are thin, start about 1–2 mm clear of the object outline, and extend about 2–3 mm beyond the dimension line.

Arrowhead length is about 3 times its width; where space is short, arrowheads are placed outside and the dimension line is extended.

Leader lines are thin and inclined, ending in an arrowhead or dot on the feature; they are never horizontal and never curved.

Aligned system: dimension figures read from the bottom or from the right-hand edge of the sheet; unidirectional system: all figures read from the bottom.

Chain (continuous) dimensioning places dimensions end to end; baseline (parallel) dimensioning measures all sizes from one common datum line.

Hidden edges use short dashes of equal length with equal gaps; centre lines use long-short-long dashes and extend 2–3 mm past the circle.

To bisect a line: arcs of equal radius greater than half the length from both ends intersect; the line joining the intersections is the perpendicular bisector.

To divide a line into n equal parts: draw an auxiliary line at any angle, step off n equal divisions with dividers, join the last point to the line end, then draw parallels.

To construct a regular polygon of n sides on a given side: use the exterior angle 360°/n; each interior angle is (n − 2) × 180°/n.

Regular polygon interior angles: triangle 60°, square 90°, pentagon 108°, hexagon 120°, octagon 135°.

A hexagon is constructed by stepping the circumradius around the circle; hexagon across flats = √3 × circumradius, across corners = 2 × circumradius.

Representative fraction (RF) = drawing length / actual length; scale = 1/RF. Plain scale shows two units, diagonal scale shows three (e.g. m, dm, cm).

Diagonal scale: divide the first unit into 10 parts, erect a rectangle, divide its height into 10 parts, and draw diagonals to read the second decimal place.

Length of scale = RF × maximum length to be measured; the scale must state its RF and the units of both the primary and secondary divisions.

To draw a tangent to a circle from an external point: bisect the line joining the point to the centre; the circle on that diameter meets the given circle at the tangent points.

First-angle projection (IS convention): the object lies between the observer and the plane; the view from the front is placed above the top view, and the left-side view is placed on the right.

Third-angle projection: the plane lies between the observer and the object; the top view is placed above the front view and the right-side view on the right.

A point's projections: front view shows true height above HP, top view shows true distance from VP; distance of front view from XY equals distance of point from HP.

A point in the first quadrant lies above HP and in front of VP; front view above XY, top view below XY.

A line parallel to both HP and VP shows true length in both front and top views; a line parallel to HP and inclined to VP shows true length and true inclination in the top view.

A line inclined to both planes: true length is found by rotating the top view (or front view) to parallel and projecting; true angles appear only after the auxiliary rotation.

A line perpendicular to HP appears as a point in the top view and true length in the front view.

A plane parallel to VP appears true shape in the front view and as an edge (line) in the top view; a plane perpendicular to both HP and VP appears as a line in both views.

Traces: HT is where the line meets HP (found in the top view), VT where it meets VP (found in the front view); both lie on XY when the line is parallel to a plane.

Solids are classified as polyhedra (prism, pyramid: plane faces) and solids of revolution (cylinder, cone, sphere: curved surfaces).

A right regular prism has two parallel polygonal bases; a pyramid has one base and triangular faces meeting at an apex.

In the simple position a solid rests on HP on its base with its axis perpendicular to HP; the top view of a vertical prism is its true base shape.

When a solid's axis is inclined to HP, draw the top view first with the axis parallel to VP, then tilt the top view and project the front view.

Section plane: a plane perpendicular to VP and inclined to HP gives a section true shape in the top view after auxiliary projection; a plane parallel to HP cuts a prism in a true-shape polygon.

A section plane parallel to the axis of a cylinder cuts a rectangle; inclined to the axis it cuts an ellipse; parallel to one generator it cuts a parabola.

A cone cut by a plane parallel to the base gives a circle, inclined to the base an ellipse, parallel to a generator a parabola, and parallel to the axis a hyperbola.

True shape of section is obtained by an auxiliary plane parallel to the cutting plane; project the section points perpendicular to the cutting plane's edge view.

Frustum: the portion of a solid between the base and a section plane parallel to the base; its lateral surface is developed as a trapezium (prism) or part of a sector (cone).

Development is the true shape of a surface unfolded onto a plane; only developable surfaces (planes, cylinders, cones) have exact developments.

Right prism development: a rectangle of width equal to the base perimeter and height equal to the prism height, divided into as many panels as base sides.

Cylinder development: rectangle of width πD and height h; a cone's development is a sector of radius equal to the slant height L and angle θ = 360° × (R/L).

Pyramid development: as many isosceles triangles as base sides, each with base equal to a base edge and sides equal to the true slant edge length.

To find true lengths of slant edges, use the auxiliary method: rotate each edge to parallel in the top view and project to the front view.

Method of triangulation develops oblique and transition pieces by dividing the surface into triangles and finding each side's true length.

Intersection of two cylinders of equal diameter with axes intersecting at right angles gives two straight lines in the elevation (common in T-joints).

Intersection of a cylinder and a cone, or two unequal cylinders, is a curve; points are found by cutting both solids with auxiliary planes and locating common points.

In the development of an intersecting solid, the intersection curve is transferred to the development by measuring distances along generators from a base line.

Isometric projection: three axes at 120° to each other, drawn at 30° to the horizontal; all three axes are equally foreshortened by a factor of about 0.816.

Isometric drawing (isometric scale not used) marks true lengths along the axes; the isometric length = 0.816 × true length, or true length = 1.22 × isometric length.

Non-isometric lines are lines not parallel to any isometric axis; their ends are located by coordinates and joined, never measured directly.

Isometric scale is constructed with a 45° line and a 30° line; lengths on the 30° line are the isometric lengths of the true lengths on the 45° line.

Circles in isometric appear as ellipses; a circle on the top face has its major axis horizontal and equal to 1.22D, minor axis 0.71D.

Isometric ellipse by four-centre method: construct the rhombus of the circumscribing square, then use the obtuse-corner centres for the large arcs and the rhombus centre for the small arcs.

Oblique (cavalier and cabinet) projection: the front face is drawn true shape in the plane of the paper; receding edges are drawn at an angle, usually 45°.

Cavalier oblique uses full scale on the receding axis; cabinet oblique uses half scale on the receding axis to reduce distortion.

In oblique projection the front face shows true shape, so circles parallel to the front plane remain true circles; circles on receding faces become ellipses.

Thread notation: M designates ISO metric thread; M20 means nominal diameter 20 mm, with pitch given as M20 × 2.5 for coarse default.

A bolt is specified by its nominal diameter, length and thread form, e.g. M16 × 60; the length excludes the head.

Conventional thread representation: external threads shown by a thick outline and a thin line at the minor diameter; internal threads by a thick minor-diameter circle and thin major-diameter circle, broken at about one quarter.

A nut is drawn across flats (width across flats W = 1.5D + 3 mm approximately) and across corners; hexagonal nut chamfer is drawn with arcs of radius 1.5D.

Riveted joints: lap joint (plates overlap) and butt joint (single or double strap); chain riveting and zig-zag riveting describe rivet arrangement.

Rivet hole diameter d = rivet diameter; for a plate thickness t, rivet diameter is approximately d = 6√t (mm) for structural work.

Keys transmit torque between shaft and hub: saddle key, sunk key (rectangular, square, gib-head), and Woodruff key; key width is roughly D/4 for shaft diameter D.

A cotter joint uses a tapered cotter through a slot to lock a rod in a socket or eye; cotter thickness is about t/4 of the rod diameter and taper 1 in 48.

Bearings: journal (plain) bearing supports a rotating shaft on a lubricated surface; ball and roller bearings are anti-friction bearings drawn with the inner and outer races and the rolling elements.

A building drawing set typically comprises the site plan, foundation/centre-line plan, floor plan, elevation(s) and section(s), plus a title block.

Floor plan: cut horizontally about 1.2 m above floor level; walls shown as two parallel lines with the thickness to scale; openings shown with door/window symbols.

Standard scales: site plan 1 : 500 or 1 : 1000; floor plan 1 : 50 or 1 : 100; detail sections 1 : 20 or 1 : 10.

Doors are drawn with a quarter-circle swing arc; a door is designated D1, D2 etc., windows W1, W2, with size given as width × height in mm.

Elevation shows external face with floor levels, plinth level, lintel level, roof level and parapet; level marks use a downward triangle with the reduced level in metres.

Section shows the cut through walls, foundation, floor, roof slab and lintel; hatching indicates cut masonry (diagonal lines) and concrete (dots and small triangles).

A foundation trench plan gives centre lines of walls (dash-dot) and the width of the trench on both sides of the centre line.

A staircase plan shows tread, riser, going, width of flight and landing; the number of risers = floor height / riser height, and number of treads = number of risers − 1 per flight.

North line (compass direction) is shown on the plan; the scale bar and the title block with drawing number, scale and date complete the sheet.