Maharashtra SSC Engineering Drawing ITI common mistakes
Maharashtra SSC Engineering Drawing ITI · Understand the traps and how to avoid them.
Using a 2H or harder pencil for freehand lettering and dimension figures so strokes are faint, uneven and partly invisible after scanning, instead of reserving HB/2H for construction lines and using a sharp HB or H for lettering.
Candidates treat 'hard pencil = accurate drawing' as a universal rule and never switch grades between construction work and finished lettering, so the graded lettering strokes come out thin and broken.
What to do instead
Adopt a fixed pencil kit discipline: 2H sharpened to a long conical point for construction and centre lines, H for visible outlines of lettering guides, HB for freehand letters and dimension numerals. Practise one A3 sheet of single-stroke vertical capitals at 10 mm, 7 mm and 5 mm heights before the exam so the grade-to-stroke feel is automatic.
Drawing dimension lines that touch or cross extension lines, placing arrowheads outside small dimensions without a leader, and omitting the gap between the object outline and the start of the extension line.
Candidates copy the look of finished drawings without knowing the spacing rules, and under time pressure they draw the dimension line exactly between the two extension lines because it 'looks closed'.
What to do instead
Memorise the spacing convention: a 1–1.5 mm gap between object and extension line, extension line projecting 2–3 mm beyond the dimension line, arrowheads touching the extension lines from inside, and for dimensions under about 10 mm the arrows placed outside with the dimension figure on a leader. Redraw any practice dimension set until all three checks pass at a glance.
In orthographic projection, drawing the top view in line with the front view but then placing the side view on the wrong side, or drawing first-angle and third-angle layouts mixed on the same sheet.
The symbol for the method is memorised as a picture rather than as a rule about where the view goes relative to the observer and the object, so candidates default to whichever layout they practised last.
What to do instead
Fix the rule in words: in first-angle projection the object sits between observer and plane, so the view from the left is drawn on the right and the view from above is drawn below. Before starting any sheet, sketch the truncated-cone symbol in the title block and state the method in writing, then lay out all three views with construction lines from a single 45° mitre line.
Losing the true shape of a section because the cutting plane is drawn at an arbitrary angle, the hatching is drawn at 45° to the paper rather than 45° to the principal outline, or hatching is continued across a hole or a rib.
Hatching is treated as shading to fill space, and the rule that section lines run at 45° to the axis of the part is not connected to the purpose of showing a cut surface.
What to do instead
Draw the cutting plane trace first as a chain line with thick ends and arrows showing viewing direction, then hatch thin continuous lines at 45° to the main outline, at consistent spacing of 2–4 mm, stopping at every visible edge. Leave ribs, webs, shafts and bolts unsectioned when cut longitudinally, and add the label A–A to match the section view.
In development of surfaces, developing a truncated or inclined solid by measuring along the slant edge instead of using true lengths obtained by rotation or auxiliary view.
Candidates transfer apparent lengths straight from the elevation, forgetting that a foreshortened line in one view is not its true length, so the development is short or skewed.
What to do instead
Use the standard method sequence: divide the base circle into 12 equal parts, project generators to the elevation, obtain true lengths of cut generators by rotating them parallel to the reference plane, then step the 12 base divisions along a straight line in the development and set off each true length on its generator. Check the total developed width equals the circumference, about 3.14 times the diameter.
Writing tolerance values as '50 ±0.05 mm' on a drawing but calculating limits, allowances and fits using nominal sizes only, so hole and shaft limit sizes, maximum and minimum clearance, and the type of fit are all reported wrongly.
The ISO hole-basis notation (for example 50 H7/g6) is memorised as a label rather than decoded into upper and lower deviations from tables, and candidates do not distinguish allowance from clearance.
What to do instead
For every fit question, tabulate four numbers before answering: hole upper and lower limits, shaft upper and lower limits. Then compute maximum clearance as hole max minus shaft min, minimum clearance as hole min minus shaft max, and classify the fit from the signs. Practise with H7/g6 (clearance), H7/k6 (transition) and H7/p6 (interference) at 25 mm and 50 mm until the table is routine.
Drawing an isometric view by setting off true lengths along the 30° axes for an object that has inclined or non-isometric faces, and drawing ellipses for circles with the major axis horizontal instead of perpendicular to the axis of the circle.
The isometric scale and the ellipse axes are learned as isolated facts, so candidates use full scale for everything and draw circles as freehand ovals oriented by eye.
What to do instead
Use isometric scale 0.816 for true isometric lengths (or accept full scale only for isometric drawing and say so). For each circle, locate its centre, draw the major axis at right angles to the axis of the cylinder and equal to 1.22 times the diameter, the minor axis equal to 0.71 times the diameter, and construct the ellipse through the four-centre method. Mark the axes on the drawing before inking.
In projection of points and lines, marking the front view and top view in the wrong quadrants, or stating the true length and inclinations without reducing an inclined line to a line parallel to a reference plane first.
The four-quadrant convention and the auxiliary-plane method are abstract, and candidates try to read true length directly from the given view.
What to do instead
Always start from the reference line XY and the quadrants: above XY is the front view, below XY is the top view, distance from XY equals distance from the corresponding plane. For an inclined line, draw the line parallel to the reference plane in the first view to get true length and one inclination, then rotate to the second position to get the other inclination, and verify that the true length is the same in both constructions.
Sketching a hexagonal bolt head or nut in plan as a circle instead of the correct across-flats and across-corners construction, and drawing key and keyway proportions from memory rather than from the standard ratio.
Fasteners and keys are drawn rarely in class compared with geometric constructions, so candidates fall back on a generic circle-and-square shape and guess widths.
What to do instead
Learn one proportional construction and reuse it: bolt head across flats W, head height 0.7D, nut height 0.8D, with the plan drawn as a hexagon inscribed in a circle of diameter 1.5D and the chamfer arcs constructed from the corners. For keys, use the standard proportions for the shaft diameter (for example a parallel key width about one quarter of the shaft diameter) and always show the keyway depth in the sectional view.
Leaving construction lines in the final inked drawing, or erasing them before the final lines are drawn so the drawing loses its centre lines and symmetry references.
Candidates ink the answer first and then rub out everything faint, which removes the centre lines and mitre lines that carry marks, or they never clean up at all because they run out of time.
What to do instead
Work in a fixed order: light 2H construction and centre lines, check geometry, then ink visible outlines with H/HB, then add hidden, centre and dimension lines, and leave construction lines in place if the question asks for the construction. Only erase smudges and wrong trial arcs. Build in a five-minute final check for line weight contrast and centre-line continuity.