Drawing Instruments and Lines

Introduction

In the Junior School CBC (KICD), Pre-Technical Studies introduces graphic communication. Technical drawings must be accurate, clear and follow standard conventions so that anyone can understand and build from them.

Drawing instruments

Types of lines

• Outline (thick continuous): visible edges.
• Construction (thin continuous): light guide lines.
• Hidden detail (short dashes): edges not visible.
• Centre line (long and short dashes): centres of circles and symmetry.
• Dimension lines (thin with arrowheads): show measurements.

Layout of a drawing sheet

Border, title block (name, date, scale, title), then the drawing. Keep drawings neat and use capital letters for text.

Basic constructions

1. Bisecting a line: with a compass at each end, using more than half the length, draw arcs above and below; join the intersections.
2. Perpendicular at a point: use a set square or compass arcs.
3. Angle of 60 degrees: draw an arc from the line's end and mark the same radius from the arc.

Worked example

To draw a 10 cm line bisected: draw AB = 10 cm. Set the compass to 6 cm. Draw arcs from A and B above and below. Join the two crossing points; the crossing on AB is the midpoint at 5 cm.

Care of instruments

Keep pencils sharp, wipe the board, store instruments in a case.

Try it

• Draw a 12 cm line and bisect it.
• Draw a rectangle 8 cm by 5 cm with dimension lines.
• Name the line types used to draw a hole inside a block.