§1The drawing as a contract
A production drawing succeeds when a maker who has never met the designer can build the part, check it, and prove it conforms — with nothing left to ask.
That standard settles most style arguments. A complete sheet carries: enough views to fix every feature; every dimension exactly once; tolerances on everything that matters (and a general-tolerance note for everything that doesn’t); material, finish and treatment; and a title block owning the sheet — number, revision, scale, projection symbol, drawn/checked signatures. Revision control is part of the contract: a changed drawing gets a new revision letter and a change note, never a silent edit. In Australia the governing conventions are the AS 1100 series; internationally, the ISO drawing standards — the practices below are common ground.
Contents§2Projection — first and third angle
Both systems unfold a part’s faces onto flat paper; they differ only in which side of the front view each unfolded face lands on.
In third-angle projection — the common practice in Australia and North America — each view is placed on the side of the part it is seen from: the top view sits above, the right-side view sits to the right. In first-angle — traditional European practice — the view is projected through the object to the far plane, so everything lands opposite: top view below, right view on the left. The two are mirror bookkeeping of the same information, and confusing them puts holes on the wrong side of real parts, which is why the frustum symbol in the hero drawing is mandatory in the title block. Read the symbol before reading the sheet.
Contents§3The language of lines
Line weight and pattern carry meaning before a single dimension is read.
| Line | Appearance | Says |
|---|---|---|
| Visible outline | thick, continuous | edges you can see |
| Hidden detail | thin, short dashes | edges behind the surface |
| Centre line | thin, long-short chain | axes and symmetry — also the anchor for position dimensions |
| Dimension / projection | thin, continuous, arrowed | measurement scaffolding, never part of the shape |
| Cutting plane | thick-ended chain with arrows | where a section is taken and which way it looks |
| Section hatching | thin, 45° equal-spaced | solid material cut by the plane |
| Phantom / alternate position | thin, long–double-short chain | moving parts’ other positions, adjacent parts |
| Break line | thin, ruled with zig-zags | a long uniform piece shortened to fit the sheet |
§4Views and sections
Use the fewest views that leave nothing ambiguous — and when the inside matters, cut the part open on paper instead of drowning it in hidden lines.
Most parts need two or three orthographic views; simple turned parts often need one plus a diameter symbol. When interiors dominate, a section replaces hidden dashes with cut, hatched material: a full section cuts straight through; a half section shows half cut and half whole on a symmetric part; an offset section jogs the cutting plane through features that don’t line up; revolved and removed sections drop a cross-section right on or beside a long member — the standard way to show a spoke or rib profile. Two conventions save confusion: ribs, webs, shafts and fasteners are not hatched when the plane runs along them (hatching would fake solidity), and hatching on one part keeps one direction so adjacent parts in an assembly can alternate.
Contents§5Dimensioning discipline
Dimension the function, once, from a datum — three habits that between them prevent most shop-floor arguments.
Once: every size appears exactly one time; duplicates eventually disagree. Function: dimension what the part must do (hole centres from the mating face), not what is easy to draw. Datum: measure features from a common reference, not from each other, because chained tolerances add up:
Three steps each dimensioned 20 ± 0.1 in a chain put the last face at 60 ± 0.3 — the errors stack. Dimensioned from one datum face as 20, 40, 60 each ± 0.1, no face is worse than ± 0.1. Same part, same tolerances, three times the certainty — for free. (Chain dimensioning is chosen deliberately only when the step itself is the function.)
Housekeeping that reads as competence: dimensions outside the outline, on the view that shows the feature’s shape; smaller dimensions inside larger; leaders to a hole’s edge pointing at its centre; diameters as Ø and radii as R; and no dimensioning to hidden lines — cut a section instead.
Contents§6Sheets and scales
ISO paper is a geometric series: every size is the previous one halved, and every size has the same √2 proportions — which is why a drawing photocopies between sizes without distortion.
| Size | Dimensions | Area |
|---|---|---|
| A0 | 841 × 1189 | 1.000 |
| A1 | 594 × 841 | 0.500 |
| A2 | 420 × 594 | 0.249 |
| A3 | 297 × 420 | 0.125 |
| A4 | 210 × 297 | 0.062 |
| A5 | 148 × 210 | 0.031 |
| Each size is the previous one halved across its long edge; the proportion stays 1 : √2 throughout, and A0 is defined as one square metre — which is why every A-size photocopies onto the next without distortion. | ||
On a 1 : 5 sheet a slot measures 37 mm on paper: the feature is 37 × 5 = 185 mm. But the printed dimension figure always states true size — scaling off a drawing with a rule is the last resort, and modern practice marks it DO NOT SCALE. Preferred scales run 1:2, 1:5, 1:10 … for reduction and 2:1, 5:1, 10:1 … for enlargement, with 1:1 the default whenever the part fits.
§7Quick reference
The working core of the page on one card rack.
Projection
third angle: view on the side seen
check the frustum symbol first
Sections
full · half · offset · revolved
ribs & shafts left unhatched
Dimensioning
once · functional · from a datum
chain of n: tolerance × n
Paper
A-series: halve to descend
A4 = 210 × 297, ratio √2
Contract test
a stranger can build and check it
revise by letter, never silently