PAU Technical Drawing Applied to Plastic Arts (Cantabria) common mistakes
PAU Technical Drawing Applied to Plastic Arts (Cantabria) · Understand the traps and how to avoid them.
When drawing the front, top and side views of a piece, the candidate places each view at an arbitrary spot on the sheet and lets the projectors between views not line up, so widths in the plan do not match widths in the elevation.
They treat each view as a separate drawing copied from the object rather than as one projection system, and they start inking or shading before establishing the projection axes and the 45° transfer line.
What to do instead
Before any detail, draw the horizontal and vertical reference axes and the 45° mitre line, then block in the three bounding boxes so that plan width equals elevation width and side-view height equals elevation height. Check alignment with light projectors that you erase only after all views are consistent.
The candidate mixes first-angle and third-angle arrangement within one sheet, for example putting the plan below the elevation in one exercise and above it in the next, or placing the left-side view on the left of the elevation.
They memorise the symbol but never internalise the difference between the European first-angle convention (object between observer and plane) and the third-angle convention, and they do not read the exam statement's indication of the system to use.
What to do instead
Decide the system at the start of the exercise and write it in a corner of the sheet. For first angle: plan below elevation, view from the left placed on the right. For third angle: plan above elevation, view from the left placed on the left. Draw the corresponding truncated-cone symbol next to the title block as a self-check.
Hidden edges are omitted or drawn as continuous thick lines, and centre lines for axes of revolution are missing or drawn as ordinary outlines, so a bored hole or a symmetric part reads as solid.
The candidate focuses on the visible silhouette and treats internal features as secondary, and has not fixed the line hierarchy (thick continuous for visible edges, dashed for hidden, thin chain for axes and symmetry) in memory.
What to do instead
Before finishing, sweep each view feature by feature and ask whether it is visible from that direction; if not, add a dashed line of the correct thickness. Always add the chain line for any axis of revolution and for planes of symmetry, extending it slightly beyond the outline.
In isometric and dimetric drawings the candidate measures true lengths directly along all three axes and draws ellipses freehand as ovals, producing distorted volumes and circles that do not touch the midpoints of the enclosing rhombus.
They confuse axonometric reduction with true measurement, and they have not practised the four-centre or conjugate-diameter construction for circles in oblique projection, so they fall back on an eyeballed oval.
What to do instead
For isometric, apply the 0.816 true-scale reduction (or use the isometric scale) and remember that only along the axes are lengths undistorted; for dimetric use the stated reduction factors. Construct ellipses in each face from the circumscribed rhombus, locating the four centres and the tangent points at the midpoints of the rhombus sides, then draw the arcs.
In conical perspective the candidate places the horizon and station point arbitrarily, ignores the cone of vision, and draws parallels that should converge to a single vanishing point as slightly diverging lines.
They think of perspective as a decorative effect rather than a rigorous projection from a station point onto a picture plane, and they do not set up the ground line, horizon and principal point as a coherent system before drawing.
What to do instead
Fix the picture plane, ground line, horizon and principal point first, then place the station point at a distance giving roughly a 60° cone of vision around the principal point. Locate vanishing points by projecting directions from the station point to the picture plane, and check every receding edge against its vanishing point with a straightedge.
Dimension lines are drawn crossing extension lines, arrows point outward with no space, values are written at random angles, and radii, diameters and chamfers are labelled without the R, Ø or C prefixes.
The candidate treats dimensioning as annotation added at the end and has not internalised the standard that dimension lines sit outside the figure between extension lines, with text readable from the bottom or right of the sheet.
What to do instead
Dimension after the geometry is finished and correct. Keep dimension lines clear of the outline, put the value above a horizontal dimension line and rotated with a vertical one, use R for radii, Ø for diameters, and never dimension the same feature twice. Reserve one area of the sheet for dimensions so they do not collide with hatching.
The candidate computes a scale as a plain ratio but then applies it in the wrong direction, drawing a 1:50 detail at 50 times the size, or writing 1:50 on a drawing that was actually enlarged.
They conflate the drawing-to-reality ratio with a magnification factor and do not verify with a known reference length before committing to the full drawing.
What to do instead
Write the scale as drawing : reality and test it with one known dimension: a 2 m wall at 1:50 becomes 4 cm on paper. Mark the graphic scale bar on the sheet and use it to double-check two or three key dimensions before drawing the rest.
When solving tangencies and conic constructions, the candidate marks tangent points by eye rather than by construction, and finds the centre of an arc tangent to two lines or a line and a circle without using the locus of centres (parallel offset lines or concentric arcs).
They rely on visual approximation because the locus method feels slower, and they do not distinguish the tangent point (on the line joining centres) from an arbitrary point of contact.
What to do instead
Always construct centres as intersections of loci: offset each line by the radius, or draw concentric arcs of radius r ± R, and drop the perpendicular from the centre to the line to find the exact tangent point. Verify by checking that the centre-to-tangent distance equals the radius.
In composition and proportion analysis the candidate describes what they see ('it looks balanced') without measuring, and does not relate the layout to a regulating geometry such as the golden section, root rectangles or a modular grid.
They treat graphic analysis as subjective commentary rather than as measurement, and they lack practice in overlaying constructions onto a reproduction to test hypotheses.
What to do instead
Overlay the construction: draw the diagonals, the root-two or golden rectangle, the modular grid, and mark the measured positions of focal points and division lines. State proportions as ratios obtained from measurement (for example eye line at two-fifths of the height) and only then interpret the compositional effect.
The candidate presents a design for an object or space with attractive rendering but no orthographic views, no dimensioned general arrangement and no scale, so the proposal cannot be built or evaluated.
They prioritise the presentation image over the technical communication that the exam rewards, and they underestimate how much of the mark comes from the normalized drawing set.
What to do instead
Structure every project answer as a set: location or situation plan, orthographic views, at least one axonometric or perspective, and a dimensioned key detail, each with scale and title. Make the technical set the backbone and treat the rendering as support, checking that every dimension needed to build the object appears once.