Assam ASSEB HS Skill Engineering Drawing common mistakes
Assam ASSEB HS Skill Engineering Drawing · Understand the traps and how to avoid them.
Setting the pencil compass or divider by eye and then drawing a circle whose radius does not match the given dimension, so the whole construction drifts off the required radius.
Candidates treat the compass as a sketching tool rather than a measuring instrument; they forget that the needle point must be set on a steel rule or scale with the lead point at the exact graduation, and that the needle must be pressed deep enough not to slip.
What to do instead
Always set the radius by placing the needle on the zero end of the scale and the lead point on the graduation, adjusting the knurled nut slowly; check the setting against the scale again before drawing. Keep the compass vertical and rotate the paper or the wrist, not the compass, so the radius stays constant. Practise the 'set, check, draw' sequence until it is automatic.
Drawing outlines with a hard grade (H or 2H) and construction or centre lines with a soft grade (HB or B), producing faint, scratchy visible edges and smudged construction lines.
Candidates do not connect pencil grade to line type; they pick whatever pencil is at hand and press hard to compensate for faintness, which grooves the paper and ruins the erasing of construction lines.
What to do instead
Fix the convention in memory: 2H for construction, projection and centre lines, H for lettering guidelines and dimension lines, HB for visible outlines and freehand work. Sharpen to a long conical point with a sandpaper pad, rotate the pencil slightly while drawing to keep the point even, and use light uniform pressure so all visible lines have the same weight.
Laying out a sheet without a title block, border, or scale statement, and drawing the view at an arbitrary size that does not fit the chosen sheet.
Candidates start drawing immediately in the middle of the paper and only think about the title block at the end, by which time there is no space; they also ignore the standard sheet sizes and the reduction ratio needed to fit the object.
What to do instead
Before any line, decide the sheet size (A4, A3, A2 as specified), draw the border and title block to the standard layout, and compute the drawing scale from the overall dimensions plus space for dimensions and notes. Sketch a rough layout box for each view on scrap paper first, transfer the layout lightly in 2H, and only then draw the views in HB.
Making letters with unequal heights and slanted stems of inconsistent angle, or mixing vertical and inclined lettering on the same sheet, so the title block looks unprofessional.
Candidates draw lettering freehand without guidelines because guidelines feel like extra work; they also do not control the slope of the inclined strokes, so letters lean at different angles.
What to do instead
Rule faint 2H guidelines for the cap height and baseline and, for inclined lettering, draw a set of parallel slope lines at 75 degrees to the horizontal. Build each letter from the standard stroke order (vertical stems first, then horizontals, then curves), keep the width-to-height ratio consistent (about 3:4 for single-stroke capitals), and erase guidelines only after the lettering is complete.
Omitting the arrowhead, leaving the dimension line short of the extension lines, or placing the numeral on the dimension line where it is crossed by a centre line or another dimension.
Candidates focus on the numeric value and treat the arrowheads and gaps as decoration; they also do not plan dimension placement, so dimensions collide and they simply drop the arrowhead or the numeral to avoid clutter.
What to do instead
Follow the full dimensioning grammar every time: thin continuous extension lines with a small gap from the object, a dimension line with two filled arrowheads touching the extension lines, and the numeral above the line (or in a break for a vertical dimension). Place dimensions outside the view in order of size, smallest nearest the object, and never dimension the same feature twice.
In first-angle projection, drawing the top view above the front view and the left side view on the left of the front view, which is the third-angle arrangement.
Candidates memorise 'top view above' from textbooks drawn in third angle or from CAD default settings, and never anchor the rule to the symbol; they also do not check which projection method the question specifies.
What to do instead
Anchor the rule physically: in first angle the object sits between the observer and the plane, so the top view goes below the front view and the view from the left is placed on the right. Draw the first-angle symbol (truncated cone with the small end toward the observer, circle on the left of the trapezium) in the title block and check the layout against it before drawing.
Projecting a point or line without marking the distances from both reference planes, so the elevation and plan do not line up on the same projector, and the true length or inclination is guessed instead of constructed.
Candidates treat the two views as independent drawings rather than as one projection linked by projectors; they also skip the auxiliary plane or rotation construction needed for true length and true inclination.
What to do instead
Always draw the XY line, mark the point's distance from the vertical plane in the plan and from the horizontal plane in the elevation, and drop or raise a single projector perpendicular to XY through both. For true length, use the auxiliary-plane or rotating-line method and label the angles with the correct reference plane; verify that the true length is never shorter than either apparent length.
Drawing the sectional view without hatching the cut surface, or hatching the whole solid including the part behind the cutting plane, and leaving out the cutting-plane line and its arrows on the adjacent view.
Candidates confuse a section with an external view and do not visualise which material the plane actually cuts; they also forget that hatching represents only the cut face, not the visible background.
What to do instead
Before drawing, sketch the cutting plane on the plan, mark the direction of sight with arrows and label it A-A. In the section, hatch only the cut area with evenly spaced thin lines at 45 degrees (reversing direction or spacing for adjacent parts), leave holes and slots unhatched, and show visible edges behind the plane as full lines. State the section title 'SECTION A-A' under the view.
Developing a surface by measuring along the slant edge instead of the true length, or developing a truncated or oblique solid with straight parallel lines where the generators are not parallel.
Candidates apply the cylinder formula to a cone or the right-cone formula to an oblique cone, and they do not first find the true lengths of the generators by projection or rotation.
What to do instead
Identify the surface type first: for a right cone, the development radius equals the slant height and the sector angle equals 360 x (base radius / slant height); for a truncated or oblique cone, divide the base into equal parts, find the true length of each generator by the rotation method, and plot each point on the development. Check the developed length against the base circumference before inking.
Drawing an isometric view with the isometric axes at 45 degrees or foreshortening the dimensions along the axes, so the drawing is not a true isometric and the box does not enclose the object.
Candidates copy the '30 degrees from horizontal' rule without understanding that isometric axes are at 120 degrees to each other, and they apply the 0.816 foreshortening factor to a drawing that is meant to be full scale along the axes.
What to do instead
Draw the three isometric axes at 30 degrees to the horizontal on each side of a vertical axis, measure full true lengths along all three (isometric drawing, not true projection), and build the object inside an isometric box. Draw non-isometric lines by locating their endpoints on the isometric axes, and use the isometric ellipse (35 degrees 16 minutes) for circles, never a compass circle.
Drawing a screw thread or a hexagonal nut and bolt from memory with the wrong proportions, e.g. thread depth equal to half the diameter or a nut whose across-corners is not about twice the nominal diameter.
Candidates do not know the standard simplified thread conventions or the empirical proportions used in machine drawing, and they have not practised the conventional representation of external and internal threads.
What to do instead
Memorise the conventions: for an external thread, the major diameter is a thick line and the minor diameter a thin line at about 0.85d; in a section, hatching runs up to the major diameter and the thread is shown by a thick line at the root. For a hexagonal bolt head, use the standard proportions (head height 0.7d, across-flats 1.5d, across-corners about 1.73d) and draw the chamfer arcs with the correct radius.
Drawing a plan of a building without wall thickness, or showing doors and windows as rectangles without swing arcs and sill or lintel levels, and omitting the north line and scale.
Candidates treat a building plan as a diagram of rooms rather than a scaled construction drawing, and they have not learned the standard symbols and the level notation used in civil drawings.
What to do instead
Draw walls to the specified thickness (commonly 230 mm or 300 mm for main walls) as two parallel lines, show openings with the correct symbol (door leaf and swing arc, window as a thin double line within the wall), mark floor levels with the level symbol and dimension the room sizes and the overall dimensions. Add the north arrow, the scale, and a title block with the drawing name and date.
Using CAD layers and object snaps carelessly: drawing on layer 0, snapping to the wrong point, or leaving the grid and ortho settings on so lines jump to unintended positions.
Candidates learn CAD commands without learning drawing management; they rely on the mouse and visual alignment instead of coordinate entry and object snaps, and they do not set up layers before drawing.
What to do instead
Set up layers for outlines, hidden lines, centre lines, dimensions and text with the correct linetypes and lineweights before drawing anything, and keep layer 0 empty. Use object snaps (endpoint, midpoint, intersection, perpendicular) deliberately, enter precise coordinates or relative polar coordinates for exact lengths, toggle ortho and grid off when not needed, and check the drawing with a zoom-extents and a plot preview before submission.