Technical Drawing Training Lesson 1: Introduction, Paper Sizes, Title Block and Scale

Technical drawing is the common language of manufacturing. A designer in one country, a machinist in another and an inspector in a third all understand the same sheet of paper the same way — because everything on it follows agreed rules. Learning those rules is what this course is about.

Before you draw a single line you have to settle three things: which sheet size you will use, where the frame and the title block go on it, and at what scale the part will be drawn. This first lesson covers exactly those three.

What is a technical drawing?

A technical drawing is not a picture of a part — it is a complete manufacturing instruction. A photograph shows you what something looks like; a technical drawing tells you how big it is, how accurate it must be, how smooth its surfaces have to be and what it is made of. Nothing on it is decorative and nothing is left to interpretation.

• It is drawn to standards (ISO, EN, TS) so that everyone reads it identically.
• It is unambiguous — a drawing that can be read two ways is a faulty drawing.
• It is complete — every dimension needed to make the part is written on it.
• It is measurable — every requirement on it can be checked with an instrument.

Drawing instruments

Most drawings are produced in CAD today, but a technical drawing course still starts on paper, because line weight, scale and view layout are learned fastest by drawing them by hand. The basic kit is:

• Drawing board: a flat surface the sheet is taped to.
• T-square: its head rests against the left edge of the board; slide it up and down to draw parallel horizontal lines. Vertical and inclined lines are drawn with a set square resting on it.
• Set squares: one 45° and one 30°–60°. Combined with the T-square they give every angle that is a multiple of 15°.
• Compasses for circles and arcs; a French curve for curves that compasses cannot draw.
• Protractor and templates for measuring angles and for drawing circles and lettering quickly.
• Pencils: the H range is hard, the B range is soft. Use 2H–H for thin and construction lines, HB–B for thick outlines and lettering.

Drawing sheet sizes: the A series

Drawing paper sizes are standardized in the A series (ISO 216 / TS 506). The whole system is built on one sheet: A0, which measures 1189 × 841 mm and has an area of exactly one square meter. Its sides are in the ratio 1 : √2.

Every smaller size comes from halving the longer side of the size above it. Halve A0 and you get two A1 sheets; halve A1 and you get A2, and so on. Because of the √2 ratio, the proportions stay the same at every step — which is why a drawing can be photocopied from A3 to A4 without distortion.

Frame and margins

Nothing is drawn right up to the edge of the sheet. A frame is drawn inside the paper edge and all drawing work stays inside it. The margins are not arbitrary:

• On A4 the frame is 5 mm from the top, bottom and right edges.
• On A3 and larger it is 10 mm from those edges.
• The left margin is always 20 mm, on every size — this is the filing edge, where the sheet is punched or bound.
• The frame is drawn with a continuous line about 0,5 mm thick.

The title block

The title block is the identity card of the drawing. It always sits in the bottom right corner, touching the frame, so that it is visible when the sheet is folded to A4. Its width is 185 mm on A4 and 180 mm on A3 and larger.

An industrial title block carries at least: the part name, the drawing number, the material, the quantity, the scale, the projection method (first angle or third angle), who drew it, who checked it, and the date. A school title block is a simplified version of the same thing.

Folding drawings for filing

Sheets larger than A4 do not fit a file, so they are folded down to A4 (210 × 297 mm). Folding follows three rules:

1. Horizontal folds are made first, then vertical folds.
2. When folding is finished the title block must be on top and fully visible.
3. Only one fold layer is punched for filing — never all layers together.

Example: an A3 sheet (297 × 420) becomes A4 (297 × 210) with a single vertical fold. The 20 mm left margin exists for exactly this purpose: it is the strip that is punched or bound.

Scale

Real parts are rarely the size of a sheet of paper. Scale is the ratio between the size drawn and the real size:

Scale = drawn size ÷ actual size

• 1 : 1 — full size. What you see is what the part measures.
• 2 : 1, 5 : 1, 10 : 1 — enlargement, used for small parts.
• 1 : 2, 1 : 5, 1 : 10 — reduction, used for large parts.

Standard scales are chosen from the series in ISO 5455 (TS 3532). Arbitrary values such as 1:3 or 1:7 are not used.

Other rules about scale

• Whatever the scale, the true dimension is written on the drawing.
• Angles are never scaled. Enlarge a part five times and a 45° angle is still 45°.
• The scale is written in the title block (or under the view) in 5–7 mm lettering.
• If one part of a drawing is not to scale, the dimension figure for that part is underlined.
• A small feature drawn separately at a larger scale is a detail view; its own scale is written next to the detail letter.
• Choose the sheet first, then the scale that fits the part onto it.

Test yourself

1. What are the dimensions of A3?
   420 × 297 mm — twice an A4 sheet.
2. Why is the left margin always 20 mm?
   It is the filing edge. The sheet is punched or bound there, so no drawing content may fall in that strip.
3. A drawing is at 1:2 and a shaft is dimensioned “40”. How long is the real shaft?
   40 mm. The dimension figure is always the real size; only the drawn length is halved.
4. Where is the title block and why there?
   Bottom right corner. When a large sheet is folded down to A4 the title block stays on the outside and remains readable.
5. Which sheet has an area of exactly 1 m²?
   A0, 1189 × 841 mm.
6. Can you scale a dimension off the paper with a ruler?
   No. Printing, copying and paper stretch all change the drawn size. Only written dimensions are valid.