MSCE Technical Drawing cheat sheet

Standard sheet sizes (ISO A series) are derived from A0 = 1 m² with a √2 side ratio; each smaller size halves the longer side, so A4 = 210 × 297 mm.

A2 drawing board is the usual minimum for A3 sheets; the T-square stock slides along the board's working edge and the blade gives horizontal reference lines only.

Set-square pairs are 45°-45°-90° and 30°-60°-90°; combined with the T-square they produce 15° increments (15°, 30°, 45°, 60°, 75°, 90°).

Compass and dividers: compass draws circles, dividers transfer measurements; a bow compass handles radii below about 25 mm more accurately than a large compass.

Pencil grades: H or 2H for construction and layout lines, HB or B for visible outlines and lettering, 2B–4B for freehand sketching; harder lead = thinner, lighter line.

Erasing shield masks adjacent lines; erase along the line direction, never across it, to avoid lifting the paper surface.

French curve and flexible curve are used for irregular curves; draw through at least three plotted points and rotate the template to keep the curve tangent-smooth.

Protractor measures and sets angles in degrees; for precise angular work use a bevel protractor or set the angle by chord/trigonometric construction instead.

Perpendicular bisector of AB: arcs of equal radius (> half AB) from A and B intersect above and below; the line joining intersections is perpendicular to AB and bisects it.

Bisect an angle: arc from the vertex cuts both arms; equal arcs from those two points intersect on the bisector line through the vertex.

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

Regular polygon construction: for a hexagon use compass radius equal to the circumradius stepped around the circle; for a pentagon use the 72° central angle or the diagonal-to-side golden ratio 1.618.

To draw a tangent from an external point P to circle centre O: bisect OP, draw a semicircle on OP; its intersections with the circle are the tangent points.

Ellipse: trammel or concentric-circle method uses major axis 2a and minor axis 2b; a point on the ellipse satisfies PF1 + PF2 = 2a (foci distance from centre c = √(a² − b²)).

Parabola: a point is equidistant from the focus and the directrix; in a rectangle of width w and height h, offsets vary as the square of the distance along the axis.

Involute of a circle: divide the circle into equal parts, step off the corresponding arc lengths along successive tangents, and join the ends to give the involute curve.

First-angle (ISO/European): the object sits between observer and plane, so the view from the front appears on the plane behind - top view goes below the front view, left-side view goes on the right.

Third-angle (US/ASME): the plane sits between observer and object, so the top view is above the front view and the right-side view is to the right.

First-angle symbol: truncated cone with the small end facing the observer and the two circles shown on the right of the elevation; third-angle symbol shows the circles on the left.

Principal views are front, top and side (right or left); align views by projection - heights transfer horizontally, depths transfer by 45° mitre line or compass arc.

Hidden detail is shown as short dashes of equal length; centre lines are long-short-long chains that extend slightly beyond the outline.

Visible outlines: continuous thick line (about 0.5–0.7 mm); hidden: dashed medium; centre lines and symmetry: chain thin; construction lines: continuous thin.

Choose the front view to show the most characteristic shape and the fewest hidden lines; a cylinder's axis is normally shown horizontal or vertical, not inclined, unless required.

Adjacent views must share one dimension: front and top share width, front and side share height, top and side share depth.

A cutting plane is shown on an adjacent view as a chain line with thick ends and arrows pointing in the viewing direction, labelled A–A.

Hatching (section lining) uses thin continuous lines at 45° to the principal outline; adjacent parts in an assembly are hatched in opposite directions or at different spacings.

Do not hatch: shafts, bolts, nuts, rivets, pins, keys, webs and ribs cut longitudinally, nor standard parts such as bearings and gears when cut lengthwise.

A half section removes one quarter of the object and shows half in section, half in outside view; the dividing line is a centre line, not a visible edge.

A broken-out (local) section is bounded by a thin irregular freehand break line; it is used to expose a small internal feature without sectioning the whole part.

A revolved section is drawn on the view itself, rotated 90° about the axis; a removed section is drawn elsewhere and labelled.

Section lines must not run parallel or perpendicular to the main outlines, and hatching must stop at visible and hidden outlines.

Thin features such as gaskets, sheet metal and profiles may be shown solid black in section when their thickness is too small to hatch.

Isometric axes are 120° apart (30° above horizontal each side); all three axes are foreshortened equally, but isometric drawings are drawn full scale along the axes.

In true isometric, lines not parallel to an isometric axis are non-isometric and must be drawn by boxing in coordinates; circles appear as ellipses with major axis 1.22 × D and minor axis 0.71 × D.

Isometric ellipse orientation: the major axis is perpendicular to the axis of the cylinder - a circle on the top face has its major axis horizontal.

Cavalier oblique: front face true shape, receding axis at 45°, full depth scale; cabinet oblique uses half depth scale to reduce distortion.

Oblique projection suits objects with a dominant flat face; circles on the front face remain true circles.

One-point perspective: one vanishing point for receding lines, front face parallel to the picture plane; two-point perspective uses two vanishing points on the horizon line.

In perspective, all lines parallel to a given direction converge at that direction's vanishing point; vertical lines stay vertical only in one- and two-point perspective with a level eye.

Isometric drawing is preferred for technical illustration because dimensions can be scaled along the axes; perspective is preferred for realistic presentation.

Dimension lines are thin continuous lines terminated by arrowheads; extension lines start about 1 mm from the object and extend about 2 mm past the dimension line.

Place dimensions outside the outline where possible; the numeral sits above the dimension line, readable from the bottom or the right-hand edge of the sheet.

Never dimension to a hidden line; give diameter with Ø, radius with R, spherical radius with SR, and a square with □.

Chain dimensioning accumulates tolerance; baseline (parallel) dimensioning from a common datum avoids tolerance stack-up and is preferred for critical features.

Limit dimensions give the maximum and minimum sizes; tolerance is the difference between them; bilateral tolerance is ±x, unilateral is +x/−0.

ISO fits: hole-basis H has lower deviation zero; shaft letters a–h give clearance, j–n transition, p–zc interference. Example: H7/g6 is a close running clearance fit.

Geometric tolerance symbols: straightness -, flatness ▱, circularity ○, cylindricity ⌭, perpendicularity ⊥, parallelism ∥, position ⌖, concentricity ◎, profile ⌓.

Surface roughness Ra is the arithmetical mean deviation; the check mark with a number (e.g. Ra 3.2) specifies the maximum value, and the basic symbol alone means any method is acceptable.

A floor plan is a horizontal section cut about 1.0–1.2 m above floor level; it shows walls, openings, stairs, sanitary fittings and room labels.

A section shows the vertical relationship of foundations, floors, roof and openings; section and plan must correspond in wall positions and dimensions.

A site plan locates the building on the plot with boundaries, setbacks, access, north point and levels, typically at 1:200 or 1:500.

Scale selection: 1:100 or 1:50 for plans and sections, 1:20 or 1:10 for construction details such as eaves and stair nosings, 1:1 or 1:5 for profiles.

Wall thickness is drawn to scale; a 230 mm brick wall is one brick thick, 115 mm is half-brick, and 345 mm is one-and-a-half brick.

Door and window symbols: a door is shown as a leaf line with a swing arc; a window is shown as two or three parallel lines within the wall thickness.

Levels are marked with a filled triangle and a value in metres (e.g. +0.450), referenced to a datum such as finished floor level ±0.000.

A stair plan shows treads, risers, going, landing and direction arrow; riser + going should approximate 550–700 mm for comfortable ascent.

Thread representation: simplified shows the major diameter as a thick line and the minor diameter as a thin line; in end view the thread is a three-quarter thin circle.

Metric thread designation M20 × 2.5 means nominal diameter 20 mm and pitch 2.5 mm; a coarse thread omits the pitch (M20).

A key transmits torque between shaft and hub; a keyway depth reduces the shaft section, and the key is drawn in section with its length along the shaft.

A bearing assembly drawing shows the shaft, inner race, rolling elements, outer race and housing; in section only the cut parts are hatched, and the rolling elements are not hatched.

In assembly drawings, parts are numbered with leader lines to balloon circles; a parts list (BOM) gives item, description, material and quantity.

A coupling drawing shows the two hubs, the flexible element and the fixing bolts; alignment and clearance between hubs are critical dimensions.

Exploded assembly drawings show components separated along their assembly axes with dashed centre lines linking them; they are used for maintenance manuals.

Detail drawings give full dimensions and tolerances for one part; assembly drawings give only overall, mating and functional dimensions.

Sketching order: light construction lines first (box or centre lines), then visible outlines in a darker grade, then hidden lines and dimensions.

Freehand straight lines are drawn from the shoulder with the eye on the end point, not on the pencil tip; short strokes are joined for long lines.

Freehand circles: draw a light square or centre lines, mark the four tangent points, then draw arcs between them; ellipses are sketched in a parallelogram.

Proportions are judged by comparing lengths against a chosen unit; use the pencil held at arm's length as a sighting gauge.

Technical lettering is single-stroke Gothic (sans-serif); vertical or 15° sloped capitals are standard, with lowercase for notes.

Lettering height guidance: 2.5–3.5 mm for notes, 5–7 mm for subtitles, 7–10 mm for main titles; the height-to-width ratio for capitals is about 1:0.7.

Guide lines for lettering are drawn with an H pencil and left in place or erased only after the ink or dark lead has set.

Sketching to a grid or isometric dot paper keeps axes and proportions consistent when a drawing board is unavailable.

Model space is where geometry is created at full size (1:1); paper space (layout) holds the title block and viewports at the plotting scale.

A layer carries colour, linetype, lineweight and on/off/freeze/lock states; freeze reduces regeneration, lock prevents accidental editing while allowing snapping.

Object snaps (endpoint, midpoint, centre, intersection, perpendicular, tangent) enforce geometric accuracy; ortho and polar tracking constrain angles.

Coordinate entry: absolute X,Y; relative @ΔX,ΔY; polar @distance<angle; direct distance entry after pointing the cursor.

Blocks are named collections of objects inserted as a single entity; attributes attach text data (part number, title) that can be extracted to a schedule.

Dimensions in CAD should be associative so they update with the geometry; dimension styles control arrows, text height and tolerance format.

Plot settings: choose the plot scale (e.g. 1:100), the paper size, the plot style table (CTB/STB) and lineweight scaling; 'fit to paper' destroys scale accuracy.

DXF is the exchange format for CAD data; DWG is the native format; PDF is used for issuing drawings and should be plotted at the correct scale with a scale bar.

Sketching order: light construction lines first (box or centre lines), then visible outlines in a darker grade, then hidden lines and dimensions.

Freehand straight lines are drawn from the shoulder with the eye on the end point, not on the pencil tip; short strokes are joined for long lines.

Freehand circles: draw a light square or centre lines, mark the four tangent points, then draw arcs between them; ellipses are sketched in a parallelogram.

Proportions are judged by comparing lengths against a chosen unit; use the pencil held at arm's length as a sighting gauge.

Technical lettering is single-stroke Gothic (sans-serif); vertical or 15° sloped capitals are standard, with lowercase for notes.

Lettering height guidance: 2.5–3.5 mm for notes, 5–7 mm for subtitles, 7–10 mm for main titles; the height-to-width ratio for capitals is about 1:0.7.

Guide lines for lettering are drawn with an H pencil and left in place or erased only after the ink or dark lead has set.

Sketching to a grid or isometric dot paper keeps axes and proportions consistent when a drawing board is unavailable.

Model space is where geometry is created at full size (1:1); paper space (layout) holds the title block and viewports at the plotting scale.

A layer carries colour, linetype, lineweight and on/off/freeze/lock states; freeze reduces regeneration, lock prevents accidental editing while allowing snapping.

Object snaps (endpoint, midpoint, centre, intersection, perpendicular, tangent) enforce geometric accuracy; ortho and polar tracking constrain angles.

Coordinate entry: absolute X,Y; relative @ΔX,ΔY; polar @distance<angle; direct distance entry after pointing the cursor.

Blocks are named collections of objects inserted as a single entity; attributes attach text data (part number, title) that can be extracted to a schedule.

Dimensions in CAD should be associative so they update with the geometry; dimension styles control arrows, text height and tolerance format.

Plot settings: choose the plot scale (e.g. 1:100), the paper size, the plot style table (CTB/STB) and lineweight scaling; 'fit to paper' destroys scale accuracy.

DXF is the exchange format for CAD data; DWG is the native format; PDF is used for issuing drawings and should be plotted at the correct scale with a scale bar.