MSCE Technical Drawing common mistakes
MSCE Technical Drawing · Understand the traps and how to avoid them.
Placing the front view in the upper-left and the top view below it while labelling the sheet 'third angle', or mirroring the layout when switching conventions.
Candidates memorise 'first angle = top view below' as a phrase without linking it to the projection symbol; under exam pressure they default to whichever layout they practised most recently and then mislabel it.
What to do instead
Before drawing anything, sketch the truncated-cone projection symbol in the corner and let it dictate the layout: first angle puts the top view below the front view and the left view on the right; third angle puts the top view above and the left view on the left. Check the symbol against the layout as a final step.
Leaving hidden detail out of a view, or drawing hidden edges as continuous thick lines instead of dashed lines of the correct weight.
Candidates focus on the visible outline and stop when the shape 'looks right', forgetting that internal features such as holes and slots must still be represented in views where they are concealed.
What to do instead
Before inking a view, walk each feature from the adjacent view and ask where it projects. Use evenly spaced dashes about 3 mm long with 1 mm gaps, and where a hidden line coincides with a centre line, let the centre line take precedence.
Cutting-plane line drawn without arrows, without identification letters, or not aligned with the direction of sight, so the resulting section cannot be matched to its cutting plane.
Candidates treat the cutting plane as decoration rather than as a projection instruction, and rush it because the section itself is the part they are being marked on.
What to do instead
Draw the cutting plane as a chain line with thick ends, add arrows at both ends pointing in the viewing direction, and label the ends A-A. Then place the section view and title it 'SECTION A-A', checking that the hatching direction is consistent across all cut material in the same part.
Hatching adjacent components in an assembly with the same direction and spacing, or hatching across a shaft, bolt, rivet, or web cut longitudinally.
Candidates apply hatching as a uniform fill and do not know the convention that standard fasteners and solid cylindrical parts are left unsectioned when cut along their axes.
What to do instead
Change hatch direction or spacing for each adjacent part and keep it constant within one part. Leave shafts, bolts, nuts, rivets, keys, and thin webs unhatched when the cutting plane passes along their length, and outline them with visible lines instead.
Dimensioning to hidden lines, double-dimensioning the same feature in two views, or omitting the overall dimensions while giving every small detail.
Candidates dimension whatever view they happen to be finishing, rather than planning a dimension scheme that gives each feature exactly once in the view where it appears clearest.
What to do instead
Plan dimensions before drawing: choose a datum, dimension each feature once in its most descriptive view, avoid placing dimensions on hidden lines, and always close the scheme with overall length, width, and height. Cross out any dimension that duplicates another.
Writing a limit tolerance or fits designation that contradicts the stated nominal size, or omitting the tolerance class letter and number (for example giving only 'H7' without the shaft class, or a surface-finish symbol with no value).
Candidates memorise isolated symbols without the ISO system context, so they cannot check that upper and lower deviations are consistent with the nominal size and the chosen fit.
What to do instead
For every toleranced dimension, write nominal size, upper and lower deviations with signs, and confirm upper minus lower equals the tolerance. For fits, state both hole and shaft classes and verify whether the result is clearance, transition, or interference. Attach surface-finish values with the process symbol and the Ra number in micrometres.
Constructing an isometric drawing by setting the isometric axes at 45 degrees or by scaling lengths along the axes by 0.816 instead of using full isometric lengths.
Candidates confuse the true isometric projection (foreshortened) with the isometric drawing (full scale along axes) and misremember the 30-degree axis angle.
What to do instead
Set both receding axes at 30 degrees to the horizontal and mark full true lengths along all three axes. Reserve the 0.816 factor for true isometric projection only, and never use it in an exam isometric drawing unless the question explicitly asks for projection.
Building a perspective drawing with all verticals converging, or choosing a station point so close that the drawing distorts badly.
Candidates apply one vanishing-point rule to every line and do not appreciate that verticals stay vertical in two-point perspective, and that station-point distance controls the cone of vision.
What to do instead
Keep all vertical edges vertical, send horizontal edges to the left or right vanishing point according to their true direction, and set the station point far enough back that the whole object fits within roughly a 30-degree cone of vision. Check by extending edges to confirm they meet at the correct vanishing points.
Freehand lettering with inconsistent height, slope, and spacing, or sketching construction lines so heavily that they cannot be distinguished from the final outline.
Candidates treat lettering and sketching as low-value items and practise them least, so they have no rhythm for stroke direction or line-weight hierarchy.
What to do instead
Rule light guide lines for cap height and baseline, keep a single slope angle (usually about 75 degrees for inclined lettering), and build letters from consistent strokes top-left to bottom-right. Sketch construction and centre lines with a hard sharp pencil and light pressure, then darken only the final outlines.
In CAD, drawing without layers or object snaps, so lines do not meet exactly, dimensions do not update when geometry changes, and the plotted line weights are wrong.
Candidates transfer paper habits to CAD and treat it as a faster pencil, ignoring that CAD rewards setting up layers, line types, dimension styles, and associative dimensioning before drawing.
What to do instead
Before drawing, create layers for outlines, hidden lines, centre lines, dimensions, and text with assigned colours, line types, and plot line weights. Use object snaps and polar tracking for every connection, dimension with associative dimensions attached to the geometry, and check the plot preview to confirm line weights and text height.