Maharashtra SSC Engineering Drawing ITI cheat sheet

Standard drawing board sizes follow the A-series (A0 = 1189 × 841 mm); each lower number halves the longer side, so A1 = 841 × 594 mm and A4 = 297 × 210 mm.

ISO 5457 specifies sheet layout: drawing frame, title block at bottom right, and centring marks at the four edges of the frame.

A T-square is used only against the drawing board's working edge to draw horizontal lines; set squares clamped to it give 30°, 45°, 60° and 90° lines.

A 45° set square plus a 30°/60° set square together produce 15° increments; angles such as 75° are made by combining 45° + 30°.

Standard pencil grades run 9H (hardest) to 9B (softest); H or 2H for construction and dimension lines, HB for lettering, B or 2B for freehand sketching.

A compass is set with the needle at the centre and the lead adjusted so both points reach the same level; the lead is sharpened to a chisel edge for circles.

Scale is the ratio of drawing length to actual length; RF = drawing length / actual length, and a diagonal scale can measure to a third decimal place.

Drawing sheets are fixed to the board with tape or clips at the corners only, keeping the sheet parallel to the board edge so the T-square stays true.

IS 10714 / ISO 128 line types: continuous thick for visible outlines, continuous thin for dimension and extension lines, dashed for hidden edges, chain thin for centre lines and cutting planes.

Hidden lines are drawn as short dashes of roughly 2–3 mm with 1 mm gaps; centre lines extend 2–3 mm beyond the outline.

Lettering follows IS 9609 single-stroke Gothic style; nominal height h gives cap height h, with lowercase and numerals in fixed proportion to h.

Recommended lettering heights: 2.5, 3.5, 5, 7, 10, 14, 20 mm; the ratio of height to stroke width is 14:1 for style A and 10:1 for style B.

Dimension lines are continuous thin lines terminated by arrowheads; extension lines start about 1 mm clear of the object and extend 2–3 mm past the dimension line.

Numerals are placed above the dimension line, readable from the bottom or the right-hand edge of the sheet; aligned dimensions are preferred over unidirectional in Indian practice.

A leader line for a note or diameter ends with an arrowhead touching the feature; it is drawn at an angle, never horizontal, and has a short horizontal tail for the note.

Dimensions are never repeated; each feature is dimensioned once on the view where it appears clearest, and radii are marked R, diameters Ø, and spherical radii SR.

To bisect an angle: strike equal arcs on both arms from the vertex, then intersect arcs from those two points; the line through the vertex is the 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 division to the line end, and draw parallels.

To draw a regular polygon in a circle: divide the diameter into n equal parts; for a hexagon the compass setting equals the circumradius.

To construct a regular hexagon given the side, step the side length around a circle of radius equal to the side (circumradius = side for a hexagon).

To find the centre of an arc: draw two chords and erect their perpendicular bisectors; the intersection is the centre.

To draw a tangent from an external point to a circle: bisect the line joining the point to the centre and use that midpoint as the centre of a semicircle through both points.

To construct an ellipse by the concentric-circle method: draw circles of the major and minor axes, divide both into the same number of sectors, and project intersections.

An ellipse by the arcs-of-circles method uses two foci; the sum of distances from any point on the curve to the two foci equals the major axis.

First-angle projection (IS/ISO): the object sits between the observer and the plane, so the view from the front is placed above the top view and the left view is placed on the right.

Third-angle projection: the plane lies between observer and object, so the top view is above the front view and the right view is to the right.

Six principal views are front, top, bottom, left, right and rear; in first angle the top view goes below and the bottom view above the front view.

The front view shows length and height; the top view shows length and depth; the side view shows height and depth - the common dimension links the adjacent views.

Hidden features are shown with dashed lines; visible outlines take precedence, and a centre line takes precedence over a hidden line at the same position.

The XY reference line represents the intersection of the horizontal and vertical planes; distances of the object above/below and in front/behind are measured from it.

Inclined surfaces appear foreshortened in the view where they are inclined and true shape only in the view perpendicular to them.

Auxiliary views are projected on planes perpendicular to one principal plane and inclined to the others, used to show true shape of inclined faces.

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

A point in the first quadrant has both views above and below XY respectively - front view above XY, top view below XY.

A line parallel to HP and VP (parallel to XY) shows true length in both front and top views, both parallel to XY.

A line parallel to HP and inclined to VP: true length and true inclination to VP appear in the top view; the front view is parallel to XY and foreshortened.

A line inclined to both planes has no true length in either view; true length is found by the rotating-line or auxiliary-plane method.

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

A plane parallel to HP appears as an edge (line) in the front view and true shape in the top view.

A plane inclined to one plane and perpendicular to the other shows its true shape only in the view on the plane to which it is parallel.

Solids are classified as polyhedra (prisms, pyramids) with flat faces and solids of revolution (cylinder, cone, sphere) with curved surfaces.

A solid resting on HP on its base shows the true shape of the base in the top view and a rectangle or triangle in the front view.

When a solid is tilted, the change-of-position method first draws the solid in simple position, then rotates the view so the axis makes the required angle with HP.

A prism has two identical polygonal bases and rectangular lateral faces; a pyramid has one base and triangular faces meeting at an apex.

A cone is generated by a right triangle rotating about one leg; the slant height l = √(r² + h²).

A cylinder is generated by a rectangle rotating about one side; its development is a rectangle of width 2πr and height equal to the axis length.

In the auxiliary-plane method, a new reference line is drawn parallel to the edge view of an inclined face to obtain true shape.

A sphere shows a circle in every view; its apparent contour is a great circle perpendicular to the line of sight.

A cutting plane is shown by a chain thick line with arrows at the ends indicating the direction of sight, labelled with capital letters A–A.

Hatching (section lining) uses thin continuous lines at 45° to the horizontal, equally spaced, and never parallel or perpendicular to the outline.

Adjacent parts in an assembly are hatched in opposite directions or at different spacings to distinguish them.

Ribs, webs, shafts and bolts are not hatched when the cutting plane passes along their length; they are shown in outline only.

A half section removes one quarter of the object; the cut half is hatched and the other half shows outside view, separated by a centre line.

A revolved section is drawn on the view itself by rotating the cross-section 90° about its axis, shown in thin lines.

A broken-out section uses a freehand irregular break line to expose a small internal detail without a full section.

Section lines should not be drawn over lettering or dimensions; the area behind the cutting plane is omitted in the sectional view.

Development is the true shape of a surface unfolded onto a plane; parallel-line development suits prisms and cylinders, radial-line development suits pyramids and cones.

Development of a right cylinder: a rectangle of width equal to the circumference 2πr and height equal to the cylinder height.

Development of a right cone: a sector of radius equal to the slant height l, with sector angle θ = 360° × r / l.

Development of a right prism: a series of rectangles, one per lateral face, with widths equal to the true lengths of the base edges.

Development of a pyramid: triangles for each lateral face laid out around the true-length base edges, with the true length of the slant edge found by rotation.

Triangulation is used for oblique solids and transition pieces where neither parallel-line nor radial-line methods apply.

The shortest path between two points on a cylinder or cone is a straight line on the development.

Allowances for seams, laps and bend radii are added to the developed length in sheet-metal practice.

Isometric projection uses three axes at 120° to each other, with the vertical axis upright and the other two at 30° to the horizontal.

In true isometric projection all three axes are equally foreshortened by a factor of about 0.816; in isometric drawing full scale is used along the axes.

Isometric scale = true scale × 0.816 (approximately 0.82), used when measuring along isometric axes in true projection.

Non-isometric lines are lines not parallel to the isometric axes; their lengths and angles cannot be measured directly and must be located by coordinates.

An isometric ellipse for a circle on a face has its major axis equal to 1.22 × diameter and its minor axis equal to 0.71 × diameter.

In cavalier oblique projection the receding axis is drawn at full scale, usually at 45°; in cabinet oblique the receding axis is drawn at half scale.

Oblique projection shows one face true shape; the receding axis is typically at 30°, 45° or 60° to the horizontal.

Isometric drawings do not show hidden lines unless required; centre lines are drawn on isometric planes along the axis directions.

Basic size is the nominal dimension; actual size is the measured dimension; limits are the maximum and minimum permitted sizes.

Tolerance = upper limit − lower limit = maximum limit − minimum limit; it is always positive.

Fundamental deviation is the difference between the fundamental size and the nearest limit; it fixes the position of the tolerance zone.

Hole basis system: the hole's lower deviation is zero (H), and the shaft letter (a–zc) sets the fit; shaft basis uses h for the shaft.

Clearance fit: the minimum clearance is positive (hole always larger than shaft); interference fit: the maximum clearance is negative.

Transition fit: the tolerance zones overlap, so clearance or interference may occur depending on the actual sizes.

IT grades 01 to 18 give tolerances; IT01 is the finest and IT18 the coarsest, and the tolerance unit i = 0.45·∛D + 0.001·D micrometres for grades IT5–IT18.

Allowance is the intentional difference between the basic sizes of mating parts; it equals the minimum clearance in a clearance fit.

A thread is specified by nominal diameter, pitch and thread form, e.g. M20 × 2.5; coarse threads omit the pitch.

A bolt has a head and is used with a nut; a screw is threaded into one of the parts; a stud is threaded at both ends and fixed in one part.

A tap bolt passes through a clearance hole in one part and threads into the other; a through bolt passes through both parts and takes a nut.

A key transmits torque between a shaft and a hub; a sunk key is partly in the shaft and hub, while a saddle key sits on the shaft surface.

A Woodruff key is a semicircular disc key seated in a milled keyway; a splined shaft has integral keys and transmits higher torque.

A coupling joins two shafts; a rigid (muff) coupling aligns shafts exactly, while a flexible coupling accommodates small misalignment.

A flange coupling uses two flanged hubs bolted together; a universal joint permits angular misalignment between shafts.

A plain (journal) bearing supports a rotating shaft with sliding contact; a ball or roller bearing uses rolling elements and is specified by bore diameter and series.

Freehand sketching uses light construction lines first, then darkens the final outlines; proportions are judged by comparing lengths against a chosen unit.

Sketching straight lines: mark the two end points, then draw with a relaxed wrist and eye on the end point, keeping strokes short and repeated.

Reading a drawing: identify the title block for part name, scale and material, then check the views for the shape, and finally the dimensions and notes.

A drawing without a scale note is not to scale; scaled drawings state the ratio, e.g. SCALE 1:2 or 2:1.

Sectional views reveal internal features; match the cutting-plane letters on one view with the section view label to understand the cut.

A note such as '2 HOLES Ø10 THRU' means two holes of 10 mm diameter drilled through the part.

Symbols on drawings: Ø diameter, R radius, □ square, ⌴ counterbore, ⌵ countersink, and a centre line indicates an axis of symmetry.

When reading an assembly drawing, use the parts list (bill of materials) to identify item numbers, quantities and material of each component.