UPMSP Intermediate Technical Drawing common mistakes
UPMSP Intermediate Technical Drawing · Understand the traps and how to avoid them.
Students draw the border and title block but leave out the dimension of the drawing sheet format, or draw the title block in the wrong corner with the wrong fields, so the sheet fails the standard layout check before any geometry is assessed.
Candidates memorise the drawing content and treat the sheet layout as decoration; they never practise the standard arrangement of border, title block and reference grid as a separate drill, so the layout is improvised on exam day.
What to do instead
Before the exam, draw the standard sheet layout from memory five times on the actual paper size used in the exam: border margins, title block position, and the fields it must carry (name, roll number, sheet number, scale, date). Time yourself so the layout takes under five minutes and becomes automatic before you start the actual problem.
The candidate uses an H or 2H pencil for the visible outlines and a soft pencil for construction lines, producing a smudged sheet with weak, uneven final lines and heavy construction lines showing through the finished drawing.
Candidates think harder pencil equals darker final line, and they sharpen pencils to a long needle point that snaps and digs into the paper; they also never practise the two-stage method of light construction then firm final lining.
What to do instead
Fix a grading rule: 2H for construction and centre lines, H for final visible outlines, HB only for lettering. Sharpen to a medium conical point, not a needle. Practise a full drawing where every construction line is later left faint and every final line is uniformly dark, then compare line weights side by side under a lamp.
Dimension text is written at inconsistent heights and orientations, arrowheads are drawn freehand and unequal, and extension lines touch the object outline or cross the dimension line, so the dimensioning block loses marks even when the numeric value is correct.
Candidates treat dimensioning as writing numbers rather than as a standards exercise; they never measure arrowhead length or letter height and do not know the rule that extension lines start with a small gap from the object and overshoot the dimension line slightly.
What to do instead
Drill a dimensioning template sheet: draw ten dimension lines with arrowheads of fixed length (about 3 mm) and width ratio 1:3, extension lines with a 1 mm gap and 2 mm overshoot, and numerals all at the same height. Check with a scale each time. Then apply the same template to one real orthographic problem.
When constructing a regular polygon or an ellipse, the candidate erases the construction arcs and centre lines, or omits the centre lines entirely, so the examiner cannot see the method and the construction marks are lost.
Candidates want a clean final sheet and erase everything that looks like working; they do not realise that in technical drawing the construction is part of the answer and centre lines are a required line type, not clutter.
What to do instead
Adopt a rule: never erase construction lines, only lighten them. Draw centre lines as thin chain lines extending 2 to 3 mm beyond the outline. Practise one polygon and one ellipse where you deliberately leave every arc and centre line visible, and label the construction steps in the margin so the method is unambiguous.
In orthographic projection of points and lines, the candidate places the front view and top view in the wrong relative position, or plots a point in the wrong quadrant, because they mix up first-angle and third-angle conventions.
The two conventions are taught close together and candidates memorise the symbol without linking it to the layout rule; under time pressure they revert to whatever they last saw rather than reasoning from the symbol.
What to do instead
Write one sentence you can apply mechanically: in first-angle projection the top view goes below the front view and the left view goes on the right. Draw the projection symbol first on every answer sheet, then lay out views to match it. Drill ten point-and-line problems where you state the quadrant and the view positions before plotting.
While drawing the projections of a solid, the candidate draws the top view as a true shape even when the solid is tilted, or forgets to project the auxiliary view from the correct reference line, so the solid appears distorted or the tilt is not shown.
Candidates copy the standard upright-solid procedure without checking the given inclination; they do not understand that the auxiliary view is built from the edge view and that the reference line must be parallel to the inclined surface.
What to do instead
Follow a fixed sequence for every tilted solid: draw the upright solid in the simple position, obtain the edge view of the inclined face, then set the new reference line parallel to that edge and project the auxiliary view. Do three problems with a 30 degree tilt and three with a 45 degree tilt, checking each time that the reference line is parallel to the edge view.
In development of surfaces, the candidate develops the lateral surface but omits the true lengths of slant edges or the base circle, or develops a truncated solid without first finding the true shape of the cut, so the development does not fold back into the solid.
Candidates treat development as a flat pattern drawing and forget that every edge in the pattern must equal its true length; inclined edges require an auxiliary true-length construction that is skipped under time pressure.
What to do instead
Before drawing the pattern, list every edge and mark whether its true length is already visible or needs an auxiliary construction. Then build the pattern edge by edge, checking each length against the scale. Finish by drawing the base and the cut outline and verifying that the total perimeter closes.
In isometric drawing, the candidate uses the true lengths along the isometric axes instead of the isometric scale, or draws non-isometric lines at 30 degrees when they should be located by coordinates, so the drawing is over-sized or geometrically wrong.
The difference between true length, isometric length (0.816 of true) and the isometric scale construction is confused, and candidates extend the 30 degree rule to every line on the object rather than only to the three isometric axes.
What to do instead
Build the isometric scale once at the top of the sheet and use it for every measurement. For any line not parallel to an isometric axis, locate its two endpoints from the axes and join them; never measure along it directly. Do one box-shaped object and one object with an inclined face to practise both cases.
In machine drawing, the candidate draws a threaded fastener with the thread lines on the wrong side of the centre line, or shows a sectional view of a nut and bolt without hatching the cut material correctly, so the conventional representation is wrong.
The conventional representation of threads (thick line for crest, thin line for root, hidden root line in end view) is memorised as a picture rather than as a rule, and hatching direction and spacing in sections are not practised.
What to do instead
Learn the thread rule as a sentence: in the longitudinal view the crest is a thick continuous line and the root a thin continuous line; in the end view the root is a thin circle about three-quarters of a turn. Draw a bolt, nut and stud from memory, then hatch a section at 45 degrees with even spacing and check that adjacent parts hatch in opposite directions.
In building drawing, the candidate draws a plan without the correct wall thickness and scale, omits the door and window symbols, or shows the section without floor levels and hatching, so the drawing cannot be read as a building.
Candidates focus on the outline of rooms and treat wall thickness, symbols and levels as detail to add later, and they do not fix a working scale before starting, so proportions drift.
What to do instead
Fix the scale first (commonly 1:100 for a small building) and write it in the title block. Draw walls to the stated thickness with a scale, then add standard symbols for doors, windows and stairs, and in the section show floor level lines, hatching for cut walls and roof slope. Practise one single-room building completely at 1:50 and one at 1:100 to feel the difference.