Textbook of Engineering Drawing, Second Edition

4.8 Textbook of Enginnering Drawing------------------

11. To construct a pentagon, given the length of side.
    (a) Construction (Fig.4.13a)

F

1. Draw a line AB equal to the given length of side.


2. Bisect AB at P.


3. Draw a line BQ equal to AB in length and perpendicular to AB.


4. With centre P and radius PQ, draw an arc intersecting AB produced at R. AR is equal to
   the diagonal length of the pentagon.
   S. With centres A and B and radii AR and AB respectively draw arcs intersecting at C.


5. With centres A and B and radius AR draw arcs intersecting at D.


6. With centres A and B and radii AB and AR respectively draw arcs intersecting at E.
   ABCDE is the required pentagon.

2

R

A

Fig.4.13a

(b)By included angle method

1. Draw a line AB equal to the length of the given side.

2. Draw a line B 1 such that <AB 1 = 108° (included angle)

3. Mark Con Bl such that BC = AB

4. Repeat steps 2 and 3 and complete the pentagon ABCDE

Fig.4.13b

/

/

,I'

1

C

12. To construct a regular figure of given side length and of N sides on a straight line.
    construction (Fig 4.14)
    
    
    1. Draw the given straight line AB.
    
    
    2. At B erect a perpendicular BC equal in length to AB.
    
    
    3. Join AC and where it cuts the perpendicular bisector of AB, number the point 4.
    
    
    4. Complete the square ABeD of which AC is the diagonal.
       S. With radius AB and centre B describe arc AC as shown.