Sectional view -- cutting plane, hatching, voids
A sectional view reveals internal detail by imagining the object cut on a cutting plane, the nearer piece removed. Three conventions carry the marks. The cutting-plane line is a chain line, thick at its ends, lettered A-A with arrows for the viewing direction. Hatching is thin lines at 45 degrees, evenly spaced, only on the solid the plane cut. Voids -- holes, bores, slots -- are left clear. Hidden-detail dashes are normally omitted inside the section.
The four section types
The syllabus names four section types; select the right one. A whole (full) section cuts right through the whole object. A part (broken-out) section cuts a local area to expose one feature, bounded by a thin wavy break line. A revolved section takes the cross-shape of a bar or rib, rotates it 90 degrees and superimposes it ON the view. A removed section is that same cross-shape drawn to ONE SIDE, often enlarged. Revolved sits ON the view, removed BESIDE it.
Exploded view and assembly with parts list
An exploded view separates the parts but keeps them on one common centre line -- the assembly axis -- spaced in the order they are assembled. The centre lines locate each part, so keep every part on its axis. The assembly drawing shows the same parts fitted together. Each part carries a balloon -- a numbered circle on a thin leader line -- keyed to a parts list of number, name, quantity and material. Together they show what parts there are, how many, and the order.
Drawn from real examiner reports.
Hatching left off the section
A section can get the internal detail right yet lose marks by omitting the hatching, so the cut solid is not shown in section at all. After cutting on the plane, hatch EVERY piece of cut solid at 45 degrees, evenly spaced, and leave holes and bores clear. A section with the correct conventions beats a neat drawing with no hatching.
s23 P51 QB4c(i); w23 P53 QB5c -- sectional views with the hatching omitted (also divider mis-placed, wrong overall size).
Exploded parts off the centre line
On exploded tasks candidates often draw each part the right shape but place it wrongly, because they ignore the centre lines that locate the components along the axis. Parts then float off-axis or out of assembly order and the positioning marks are lost. Draw the common centre line first, then hang each component on that shared line, spaced in assembly order and direction.
s23 P52 QB4a; w23 P53 QA2 -- exploded parts drawn the right shape but wrongly placed because the locating centre lines were ignored.
Line weights only on the outer edge
Line conventions are a persistent lost mark on sections. The thick/thin technique is often applied only to the outer edge while internal parts stay one weight, so depth is lost. Use thick for cut edges and outlines, thin for hatching and projection, a thick-ended chain line for the cutting plane. Applying it to internal features, not just the perimeter, is credited.
w23 P53 QB5d(i) -- thick/thin line technique on a mould drawing applied only to the outer edge, not the internal parts.
Right shape, wrong overall size
Correct wall and base thickness is not enough if the whole part is sized wrongly. Candidates draw the internal detail accurately but do not work to the stated scale, so the overall size is out. Set the overall size from the stated scale and given dimensions rather than eyeballing it, and project internal walls and dividers from the given views so they land in the right place.
s23 P51 QB4c(i); w23 P53 QB5c -- correct wall/base thickness but wrong overall size, internal divider mis-placed.
Adjacent parts hatched the same way
In an assembly section, two parts that meet must be hatched in OPPOSITE directions (or at different spacing) so the boundary between them is visible. Hatching both the same way hides the join. Standard parts that lie ALONG the plane -- bolts, nuts, rivets, shafts, keys, thin ribs and webs -- are conventionally left UNHATCHED, because sectioning them adds no information.
Revolved vs removed section mixed up
Revolved and removed sections show the same cross-shape but PLACE it differently. A revolved section is rotated 90 degrees ON the view. A removed section is lifted OFF and drawn to ONE SIDE, often enlarged. Neither is a full section, which cuts the whole object. Ask: is the cross-shape ON the view (revolved) or BESIDE it (removed)?
Hatching the holes too
A testable error: shading the ENTIRE cut face, holes and all. Hatching means the solid material the plane actually cut through. A drilled hole or bore is empty space -- a void -- so nothing is cut there, and it is left CLEAR. Hatch across a hole and you claim solid metal where there is a gap. Rule: hatch the solid, leave the void clear, at 45 degrees evenly spaced.
Identify the section type first
Set up the named type correctly: a whole section cuts right through, a part section needs a thin wavy break line, a revolved section sits ON the view, a removed section sits to ONE SIDE. The wrong type loses the setup marks before you hatch a line.
Cutting plane and hatching conventions
Draw the cutting-plane line as a chain line thick at its ends, lettered A-A with viewing arrows. Hatch only the cut solid at 45 degrees, evenly spaced, leaving holes clear. In an assembly section, hatch adjacent parts in opposite directions and leave standard parts unhatched.
Work to scale, balloon to a parts list
Work to the stated scale, and apply correct line weights to internal detail, not just the outline. On an exploded or assembly answer, keep every part on its common centre line in assembly order, and balloon each to a parts list of number, name, quantity and material.
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