Grade 10 metalwork Related Drawing in Metalwork – Scales and Conventions Notes
Related Drawing in Metalwork — Subtopic: Scales and Conventions
Specific learning outcomes
- (a) Identify and outline the sub-sub-strands:
- Symbols, abbreviations and conventions in drawings
- Interpretation of symbols, abbreviations and conventions
- Construction of scales in technical drawing
- Application of symbols, abbreviations and conventions in drawings
- (b) Identify symbols, abbreviations and conventions used in drawings
- (c) Interpret symbols, abbreviations and conventions used in drawings
- (d) Construct scales in technical drawing
- (e) Appreciate the application of symbols, abbreviations and conventions used in drawings
Why these matter (for Kenyan learners, age 15)
Drawing conventions and correct use of scales let you share accurate information with workshop technicians, classmates and employers. In Kenya we use metric units (millimetres) in metalwork drawings. Following conventions avoids errors, saves material and keeps people safe.
Common drawing conventions and symbols
Below are simple symbols, line types and abbreviations you must know.
Line types
- Continuous thick — visible edges
- Dashed (short) — hidden edges
- Chain (long dash, dot) — centre lines
- Thick chain with arrows — cutting plane line
Symbols
- Ø — Diameter (use before size, e.g., Ø20 mm)
- R — Radius (e.g., R10)
- Section hatching — shows cut surfaces (45° lines)
- Weld symbols — fillet, groove, spot (on reference line)
- Surface finish — roughness sign with value (often in µm)
Common abbreviations
- THK or T — Thickness
- DIA — Diameter (or use Ø)
- CL — Centre line
- TYP — Typical (repeated detail)
- REF — Reference (not a controlled dimension)
- MS — Mild steel; SS — Stainless steel
Small visual examples (simple SVG)
Centre line
Hidden line
Section (hatching)
Diameter example
Interpreting symbols and abbreviations (short examples)
- Ø20 — the feature is a circle (hole or shaft) of diameter 20 mm.
- R10 — a rounded corner or fillet radius of 10 mm.
- THK 6 — plate thickness is 6 mm.
- CL next to dashed-dot line — shows the centre line of a part or hole pattern.
- Section A–A with hatching — the drawing shows a cut through the part along arrowed cutting plane A–A.
- Weld symbol (triangle on reference line) — fillet weld. The symbol placed on the reference line points where to weld and on which side.
Constructing and using scales
Always use the metric system (millimetres) and keep units consistent. Common scales in metalwork drawings:
- Full size: 1:1
- Reduction (smaller on sheet): 1:2, 1:5, 1:10, 1:20, 1:50
- Enlargement (larger on sheet): 2:1, 5:1
How to calculate sizes
For scale 1:n (reduction), Drawing size = Real size ÷ n. For scale m:1 (enlargement), Drawing size = Real size × m.
Examples- Real part 150 mm, draw at 1:5 → drawing length = 150 ÷ 5 = 30 mm.
- Real hole Ø12 mm, draw at 2:1 → drawing diameter = 12 × 2 = 24 mm.
- Decide real length for bar (say 50 mm on the object). At 1:5 this becomes 10 mm on paper.
- Draw a straight line and mark equal segments of 10 mm for each 50 mm real length or choose segments labelled 0, 50, 100 etc. and scale down.
- Label units (mm) and the scale: e.g., "Scale 1:5 — 1 unit = 5 units real".
Constructing a simple 1:2 scale (step-by-step)
Task: Draw a bar of real length 120 mm at scale 1:2.
- Calculate drawing length: 120 ÷ 2 = 60 mm.
- On drawing paper, use a ruler to mark 0 mm and 60 mm points.
- Use thin lines for dimension lines and arrows; write the real length near the dimension (120 mm) and the scale (1:2) on the title block area.
- Label material (e.g., MS), thickness, and any tolerances needed.
Classroom activities and suggested learning experiences (suitable for Kenyan technical classes)
- Identification activity: Give students copies of simple metalwork drawings and ask them to list all symbols and abbreviations used. Use metric units only.
- Interpretation exercise: Present short drawing extracts (e.g., plate with holes, welded bracket) and ask students to explain what each symbol and line means.
- Scale workshop: Students measure real objects (small bar, plate), then draw them on paper to different scales (1:1, 1:2, 1:5). Check correctness.
- Construct-to-scale practical: Using a drawing at 1:2, students set out and mark metal stock in the workshop before cutting or drilling (supervised).
- Group drawing task: In teams, create a shop drawing for a simple welded frame using correct symbols and a suitable scale. Present to class.
- Workplace link: Visit a local metal workshop or technical training institute to see real shop drawings and how workers use them.
- Assessment: Short quiz on symbol meanings, a practical drawing to scale and a quick interpretation test.
Tips and good practice
- Always put the scale clearly on the drawing (e.g., Scale 1:5) and write units (mm).
- Use thin lines for dimensions, thick lines for visible outlines.
- Place symbols and notes near the relevant feature, but keep the drawing tidy.
- Keep text clear and use capital letters for notes (common classroom rule).
- Follow the same conventions used in the workshop or technical college you aim to join — consistency matters.
Quick revision checklist (for the learner)
- Can you name three line types and their uses?
- Can you read Ø and R symbols and state sizes?
- Can you convert real measurement to drawing size for 1:2 and 1:5?
- Can you draw a simple scale bar and label it correctly?
- Can you place a weld symbol correctly on a drawing reference line?