GEOMETRICAL CONSTRUCTION: LINES

CONTENT

• Definition of Lines
• Types of Lines
• Dividing a Given Line into Equal Parts

LINES: A line is a long narrow mark made on a surface. A line may be straight, crooked or curved.

Properties of lines

1. A line has position and length.
2. A line does not have width or thickness.
3. A straight line is the shortest distance between two points.
4. A line that has more than one curve is called a crooked line.
5. Two or more lines always having equal distance apart are parallel lines.
6. A line following a circular path is a curve.

EVALUATION

1. Define a line
   1. State three properties of line.

TYPES OF LINES

Thick continuous line: This is a thick and solid line used to show visible outlines of an object.

They are also used as border lines (15mm from paper margin).

Thin continuous line: This is a thin and solid line used for dimension lines, lines, projection lines, leader lines, hatching or section lines etc.

Short dashes: The dashes are about 3mm long and spaced about 1mmfrom each other.

These are approximate values and will depend on how large the drawing might be. They  are used to represent/show hidden details.

Thin continuous chain line: These are thin lines made of long and short dashes. The long dashes can be about 19-38mm long while the short dashes may be about 1.5mm long. The length will vary with the size of the drawing and the length of centre line needed.  They are used for centre lines

Thick continuous chain with arrow head: They are thick lines made of either long and short dashes or equal sized dashes. Arrow heads are drawn on their ends to show the direction in which the section was taken. They are used for cutting and viewing planes.

Thick irregular solid lines: These are thick solid lines drawn freehand. They are either short break or long break lines used to show the part of an object that has been removed. The long break lines are drawn as thin solid lines with Z symbol inserted in several places along its length                                           or

Continuous irregular wavy lines: They are thin lines drawn freehand and are used to indicate the limit of partial views.  

Phantom lines: These are thin dashes lines drawn with one long dash followed by two short dashes. They are used to show alternate positions of moving parts. The original position is drawn with visible (thin continuous) lines while its rotated or new position is shown with phantom lines.

TYPES OF LINES

Thick continuous line: – this is used for all visible outlines. It should be the most prominent on drawing.

1. Thin continuous line: – This is used for constructing projections, extensions, hatching and leader lines.
2. Short dashes: This is used to show hidden details.
3. Thick continuous wavy or irregular line): – it is used for irregular boundary or short break lines.
4. Thin ruled line and zigzags: – This is used for long break lines.
5. Arrow head  – it is used for dimension.
6. Thin long chain line: – It is used for centre lines.
7. Thick long chain line: – It is used for cutting viewing lines.
8. Thin continuous wavy line:- It is used for limits of partial views.

.

EVALUATION

1. Mention five types of lines and state their uses.
   1. When do we use thin continuous lines?

Division of a straight line into equal parts

A line can be divided into a number of equal parts. For example, a given line can be divided into halves, fourths, eights etc.

Procedure 1

1. Draw the given line AB.
2. Draw AC any convenient acute angle and set off from A.
3. Divide the line into the number of the required parts using a pair of divider or a scale rule and a pencil.
4. Now join the points on the inclined to the line to be divided from the extreme with parallel lines.

Procedure 2

1. Draw the given line, AB.
2. Draw a line AC to meet it at any convenient angle.
3. Join CB.
4. Divide AC into the required number of parts using your ruler. Label the points 1,2,3,4…
5. From the points 1, 2, 3…. Draw lines parallel to CB to meet AB. These parallel lines intersect AB at the required points; this divides AB into equal segments.

ACTIVITY

Divide a straight line 70mm long into 5 equal parts.

GENERAL EVALUATION

1. How can horizontal and vertical line be drawn?
2. List the information required in title block.

READING ASSIGNMENT

Read about ANGLES

1. MELROSE, Basic Science and Technology, Book 2 page 56-58
2. NERDC Basic Technology for JSS book 2 page 32-39.

WEEKEND ASSIGNMENT

1. Identify this line. ___________________________________ (a) thin continuous line (b) ruled zigzag line (c) arrow head line. (d) short dashes.
2. The type of line used in showing visible outline is (a) thin continuous line (b) thick continuous line (c) thin ruled zigzag line (d)thick continuous wavy line.
3. The shortest distance between two points is _______ (a) curve (b) straight line (c) crooked line (d) parallel line
4. Which of the following is not a property of a line? (a)It has position and length  (b)It has width and thickness (c)It has virtually no thickness  (d) It may be a straight line or curved line.
5. The line that is used in showing hidden details is __________ (a) thin continuous (b) thick continuous (c) arrow hand (d) short dashes

THEORY

1. (a) Define a line.
2. Draw a line AB of 60mm and divide the line into 8 equal parts.
   1. Draw line AB equals to 10cm and divide into proportions 3:5:4.