MATSEC AM Graphical Communication common mistakes
MATSEC AM Graphical Communication · Understand the traps and how to avoid them.
Submitting a drawing where the outline is drawn with a hard 0.5 mm or HB pencil line and no line hierarchy, so construction lines, outlines and dimension lines all read with the same weight.
Candidates learn to draw with a single pencil and never practise the ISO line-group convention (thick continuous for visible outlines, thin continuous for dimension/extension/projection lines, thin chain for centre lines). Under timed conditions they default to the tool already in hand.
What to do instead
Before the exam, build a fixed pencil set: 0.5 mm HB or 2H for thick outlines, 0.3 mm 2H for thin lines, and a 0.3 mm H for chain centre lines. Practise five full drawings using only that set, and on the exam check line thickness at arm's length before inking or finalising.
Producing a third-angle orthographic layout when the question specifies first-angle projection (or vice versa), placing the plan below the front elevation instead of above it and misplacing the side view.
Candidates memorise the symbol but not the rule that links it to view placement, and many textbooks and CAD defaults use third angle, so habit overrides the instruction printed on the paper.
What to do instead
Learn the rule as a single sentence: in first angle the object sits between the observer and the plane, so the view seen from above goes below the front view. Draw the projection symbol first on every answer sheet, then lay out the three views against it before adding detail.
Leaving orthographic views unaligned, so the plan is not vertically projected from the front elevation and the side view is not horizontally projected, producing hidden detail that contradicts between views.
Candidates draw each view as an isolated picture and start in the middle of the sheet, so there is no shared baseline or projection grid to keep features in correspondence.
What to do instead
Set out faint construction lines across the sheet at 45 degrees (a mitre line) linking plan, front and side before drawing any feature. Draw one view fully, project every significant edge across with a 2H line, and only then commit outlines.
Omitting or misapplying hidden detail: either no dashed lines at all, or dashed lines drawn where a visible edge already exists, or dashes drawn through a centre line.
Hidden detail is the least intuitive part of orthographic work, and candidates fear cluttering the drawing, so they leave it out; where they do include it, they do not check which edges are actually obscured from that viewing direction.
What to do instead
For each view, list the features on the far side of the object and mark which are behind solid material. Draw hidden lines as thin dashes of consistent length with gaps, never crossing a centre line, and delete any hidden line that coincides with a visible outline.
Dimensioning that duplicates a size, chains dimensions from feature to feature instead of from a datum, or omits the overall size, so the drawing is over- or under-constrained.
Candidates treat dimensioning as labelling rather than as a specification, and they add dimensions as they draw each feature rather than planning the set of sizes needed to manufacture the part.
What to do instead
Before adding any dimension, decide the datum edges and write the minimum set of sizes that fully defines the part. Dimension each feature once only, run dimensions from the datum where possible, and include overall length, width and height. Check by asking whether a machinist could make the part from the numbers alone.
Poor arrowheads and dimension text: arrowheads drawn freehand and unequal, figures not sitting above a continuous dimension line, or dimensions written on top of the drawing rather than outside it where space is tight.
Candidates run out of time and rush the annotation stage, and small arrowheads are hard to draw consistently without practice, so they accept visible inconsistency.
What to do instead
Use a dimension template or a sharpened 2H pencil with a short, firm stroke for arrowheads, keeping them about 3 mm long and filled. Write figures in a consistent upright hand, place them above the line and unbroken by it, and move crowded dimensions outside with extension lines rather than squeezing them in.
Incorrect or missing sectional detail: hatching run across the whole assembly instead of only the cut material, adjacent parts hatched at the same angle, or no cutting-plane line and label on the related view.
Candidates copy the look of a section without understanding that hatching represents solid material cut by the plane, so they hatch voids, shafts and fasteners that are not cut.
What to do instead
Mark the cutting plane on the main view with a chain line, arrows and letters first. In the section, hatch only the areas the plane passes through, use 45-degree lines at about 3 mm spacing, reverse the angle for adjacent parts, and leave shafts, bolts and pins unhatched when cut longitudinally.
Construction that is not geometrically true: bisected angles that are visibly unequal, tangents that do not touch, an inscribed polygon whose vertices miss the circle, or an ellipse drawn as a freehand oval instead of by a stated construction.
Candidates rely on eye and freehand approximation for standard constructions, and under time pressure they skip the construction arcs that would guarantee accuracy.
What to do instead
Learn each standard construction as a fixed sequence of arcs and lines and keep the construction arcs faintly visible on the sheet. For tangency, draw the line to the exact tangent point found by construction, and check by eye along the line: a true tangent touches at one point only. For ellipses, use the concentric-circle or trammel method rather than freehand.
Isometric and oblique drawings with unequal axes, wrong axis angles, or measurements taken along the receding axis at true length in isometric, producing a distorted solid.
Candidates mix up isometric with oblique and forget that isometric axes are at 30 degrees to the horizontal with all three foreshortened equally, while in cavalier oblique the receding axis is at full scale and in cabinet oblique at half scale.
What to do instead
Draw the three isometric axes at 30, 30 and 90 degrees from a single origin using a 30/60 set square before any solid. Measure all three directions to the same scale in isometric, and state and apply the correct receding-axis scale in oblique. Box the object in first, then cut away.
Unplanned sheet layout: drawing too large or off-centre, title block incomplete or missing, no border, and no working/construction left visible where marks are awarded for method.
Candidates start drawing immediately at the first free space and treat the title block and border as decoration, so the finished sheet is unbalanced and assessment evidence for construction is lost.
What to do instead
Spend the first two minutes ruling the border and title block and sketching a light bounding box for each view, centred with equal margins. Keep construction lines faint but present, and complete name, title, scale, date and projection symbol before final checking.