National and international standards
Standards keep everyone from drawing however they like. A standardized drawing is understood the same way in Rosario as in Shenzhen, and that is exactly what manufacturing requires.
01What standardization is for
A standard is a written agreement on how things are done. In technical drawing that means that the drawing that leaves an office in Rosario is manufactured in a workshop in Shenzhen without phone calls, because both read the same thing.
| Body | Scope | Examples |
|---|---|---|
| IRAM | Argentina | IRAM 4504 sheet formats, 4502 lines, 4513 dimensioning |
| ISO | International | ISO 216 paper formats, ISO 128 representation, ISO 129 dimensioning |
| IEC | International, electrotechnology | IEC 60617 symbols, IEC 61082 documents |
| ANSI / ASME | United States | ASME Y14.5 geometric tolerancing |
| AEA | Argentina, electrical installations | AEA 90364 regulations for electrical installations |
IRAM is a member of ISO and adopts a good part of its standards, so in practice what is studied here matches the international criteria. The important differences appear with the US system: third-angle projection, inches and another family of sheet formats.
02Sheet formats
The A series starts from A0, which has an area of exactly 1 m² and a ratio between its sides of √2. That is the only ratio that is preserved when the sheet is cut in half: that is why two A4 make an A3, two A3 an A2, and so on.
| Format | Size (mm) | Area |
|---|---|---|
| A0 | 841 × 1189 | 1 m² |
| A1 | 594 × 841 | 0.5 m² |
| A2 | 420 × 594 | 0.25 m² |
| A3 | 297 × 420 | 0.125 m² |
| A4 | 210 × 297 | 0.0625 m² |
Every sheet carries a border margin—normally 10 mm, and 20 mm on the filing side for punching—and a title block in the lower right corner, with the part name, the scale, the projection symbol, the date, who drew it and who checked it, and the drawing number.
Choose the format and the scale, and check whether the part fits on the sheet with its margins and its title block.
03Scales
The scale is the ratio between the size on the drawing and the actual size. It is written drawing : actual, and the standard ones are multiples of 1, 2 and 5:
| Type | Standard values | When it is used |
|---|---|---|
| Enlargement | 2:1, 5:1, 10:1, 20:1 | Small parts: a connector, a package |
| Full size | 1:1 | Circuit boards, covers, medium-sized parts |
| Reduction | 1:2, 1:5, 1:10, 1:20, 1:50, 1:100 | Panels, rooms, installations |
Even if the drawing is at 1:10, the dimensions give the true size of the part, not that of the paper. The scale is there so that the drawing fits and looks proportioned, not so that someone measures with a ruler on the drawing.
04Lines and dimensioning
| Line | Stroke | Meaning |
|---|---|---|
| Thick continuous | ——— | Visible edges and outlines |
| Thin continuous | ——— | Dimensions, extension lines, section hatching |
| Dashed | - - - - | Hidden edges |
| Thin chain (dash and dot) | — · — · | Centerlines and symmetry |
| Thick chain (dash and dot) | — · — · | Cutting plane |
| Thin freehand | ∿∿∿ | Break or limit of a partial view |
The ratio between thick and thin lines is 2 to 1. And for dimensioning there are four rules that solve almost everything:
- Each measurement is dimensioned only once, in the view where it is seen best.
- Dimensions go outside the part whenever possible, and the small ones closer than the large ones so that the lines do not cross.
- Figures are read from the bottom or from the right, and are never crossed by a line.
- Diameters carry ⌀, radii R, and measurements are in millimeters without writing the unit.
05What an electronics engineer documents
- Enclosure drawing. With the cutouts for connectors, display and ventilation, dimensioned from a common origin so that the workshop can machine them.
- Panel layout drawing. Physical location of rails, terminal blocks and protective devices.
- Electrical schematic. With IEC or IRAM symbols and reference designators.
- Board documentation. Silkscreen, drill drawing and Gerber files: the electronic equivalent of the manufacturing drawing.
- Installation drawing. On top of an architectural plan, at 1:50 or 1:100, with the AEA symbols.
06In the lab
For five objects from the workshop, decide in which format and at which scale each should be drawn, and justify the choice. Check that the choice leaves room for dimensions and the title block.
Design your own title block that complies with IRAM 4508 and use it in all the work for the course. It is the first step toward consistent documentation.
Measure a real cover with a caliper, draw it to scale and dimension all its holes from two reference edges. Then check whether someone else could manufacture it from that drawing without seeing the part.
07Common mistakes
- Dimensioning the size on paper instead of the real one.
- Repeating dimensions in more than one view: if one measurement changes, a contradiction remains.
- Using non-standard scales, such as 1:3 or 1:7.
- Forgetting the title block or leaving it without the scale or the projection symbol.
- Writing “mm” on every dimension. It is declared once in the title block.
- Dimensioning to centerlines without indicating it, or dimensioning to hidden edges.
08Self-assessment
How large is an A0 and why?
841 × 1189 mm: it is the rectangle of 1 m² whose side ratio is √2.
How many A4 sheets fit in an A1?
Eight: each cut in half goes down one format step, and from A1 to A4 there are three cuts, 2³ = 8.
A part 1200 mm long drawn at 1:5: how long is it on paper?
240 mm. It fits on a landscape A3, which is 420 mm long, with room for dimensions.
Which line is used for a hidden edge?
The dashed one.
What does ⌀25 mean in a dimension?
A diameter of 25 mm. If it were a radius it would be written R25.
Why is the margin on the left side wider?
Because it is the filing side: that is where the punch holes or the folder binding go, and there can be no drawing there.
09Further reading
- Instituto Argentino de Normalización (Argentine Standardization Institute). Manual de normas IRAM de dibujo técnico (in Spanish; IRAM technical drawing standards manual). IRAM. Formats, lines, title block, scales and dimensioning; the local reference.
- Frederick E. Giesecke et al. Technical Drawing with Engineering Graphics. 14th ed. (Spanish edition, “Dibujo técnico con gráficas de ingeniería”), Pearson, 2013. A good treatment of dimensioning and tolerancing, with a manufacturing mindset.
- Asociación Electrotécnica Argentina (Argentine Electrotechnical Association). Reglamentación AEA 90364 para la ejecución de instalaciones eléctricas en inmuebles (in Spanish; AEA 90364 regulations for the execution of electrical installations in buildings). AEA. What governs an electrical installation drawing in Argentina.