SPM Grafik Komunikasi Teknikal common mistakes
SPM Grafik Komunikasi Teknikal · Understand the traps and how to avoid them.
Drawing hidden detail as solid continuous lines instead of dashed hidden-detail lines when a feature is not visible from the chosen view.
Candidates copy what they imagine the object looks like rather than applying the visibility rule view by view, and they forget that line type encodes visibility, not importance.
What to do instead
Before inking, run a visibility check per view: for each edge ask 'can an observer on this side see it?' Visible = continuous thick line; hidden = short dashes of even length and gap. Practise by drawing the same L-shaped block in three views and marking each edge V or H in pencil first.
Mixing first-angle and third-angle symbol placement, e.g. placing the plan above the front elevation while also drawing a third-angle symbol, or omitting the projection symbol entirely.
Both systems are taught together and the rule 'plan above = first angle, plan below = third angle' is memorised as words without being tied to the symbol drawing.
What to do instead
Always draw the truncated-cone projection symbol next to the title block and derive view placement from it: first angle puts the view of the left side on the right; third angle puts it on the left. Do three practice layouts, each time stating the angle in writing before starting.
Dimensioning to hidden lines or to a feature's projection line instead of to visible outlines, and placing dimensions inside the hatched area of a section.
Candidates dimension the geometry they used to construct the drawing rather than the finished surfaces a machinist needs, and they run out of space outside the outline.
What to do instead
Apply the rule 'dimension visible edges only, outside the outline, between extension lines with a small gap from the object'. If a feature is hidden, add a section or auxiliary view and dimension there. Reserve the hatched region purely for material indication.
Omitting or mis-stating tolerance and fit notation, e.g. writing 25.00 instead of 25.00 ±0.05, or confusing H7/h6 hole-basis and shaft-basis designations.
Candidates treat tolerances as decoration and do not connect the letter case (capital = hole, lower case = shaft) to the basis system.
What to do instead
Write limits in full: nominal, upper and lower deviation, and the ISO class. Remember capital letter = hole, lower case = shaft; the letter position (H/h) sets the fundamental deviation and the number sets the grade. Do five conversion drills between limit dimensions and ISO symbols.
Constructing an isometric drawing by scaling the orthographic lengths equally along all three isometric axes, producing a distorted object, or drawing non-isometric lines at 30 degrees.
Candidates do not realise isometric projection foreshortens true lengths to about 0.816, and they misapply the 30-degree rule to edges that are not parallel to the isometric axes.
What to do instead
Use isometric drawing (full scale along the axes) and state that choice, or apply the 0.816 factor for true projection. Only lines parallel to the three axes go at 30 degrees to the horizontal; all other edges are located by their endpoints on the isometric grid, never drawn at an arbitrary angle.
Placing the station point, horizon line and vanishing points arbitrarily so that the perspective looks plausible but violates the cone of vision, causing extreme distortion at the edges.
Candidates copy a picture's composition without understanding that the station point distance controls the field of view and vanishing-point spacing.
What to do instead
Set the horizon first, then the station point at a distance giving roughly a 30-60 degree cone of vision, and derive vanishing points from it. Keep the whole object inside the cone. Check by measuring the angle subtended at the station point by the object's widest extent.
Leaving construction lines, smudges and inconsistent line weights in the final drawing, or drawing all lines at the same thickness.
Candidates stop when the geometry is correct and treat line quality as cosmetic, and they use one pencil grade for everything.
What to do instead
Adopt a fixed hierarchy: thick continuous for visible outlines, thin continuous for dimension, extension and hatching lines, thin dashed for hidden detail, thin chain for centrelines. Finish with a construction-line erasure pass and a soft eraser dragged in one direction to avoid smudging.
Using a T-square or set square against a damaged or non-true edge of the drawing board, or sliding the set square without holding the T-square head against the board edge.
Candidates set up the sheet quickly and assume the board edge is a reliable datum, and they try to draw angles by eye.
What to do instead
Check the board edge with a straightedge first; if it is not true, tape a straight datum strip to the board. Always keep the T-square head firmly against the datum and slide the set square along the T-square blade, never along the board directly.
In CAD, drawing everything on layer 0 with the default lineweight and then trying to fix line types afterwards, and using absolute instead of relative or polar coordinates for angled geometry.
Candidates learn commands in isolation without a layer standard, and they default to typing absolute coordinates because it is the first method taught.
What to do instead
Set up a template with named layers (outline, hidden, centre, dimension, hatch) carrying linetype, lineweight and colour before drawing. Use relative (@dx,dy) and polar (@length<angle) input for angled features, and object snaps rather than typed coordinates wherever geometry already exists.
Scaling a drawing by enlarging the geometry but leaving the dimension text and title-block scale unchanged, so the stated scale no longer matches the drawing.
Candidates treat scale as a printer setting rather than a ratio that governs both geometry and annotation.
What to do instead
Decide the scale before drawing and record it in the title block. In CAD, draw full size and scale only at plot time, keeping dimension text at the correct plotted height. If geometry must be resized, update the scale note and re-check every dimension value.