S. J (GOVERNMENT POLYTECHNIC BENGALURU, ARUN KURALI LECTURER IN DEPT OF CIVIL ENGG)
ENGINEERING DRAWING
Plain Scale
A plain scale is simply a line, which is divided into a suitable number of equal parts,
the first of which is further sub-divided into small parts. It is used to represent either
two units or a unit and its fraction such as km, m and dm, etc Let us do some
examples so that you can better understand the
plain scales.
Problem 1;
Construct a plain scale to show meters when 1cm represents 4 meters and long
enough to measure up to 50metres.find the R.F. and mark on it a distance of 36
meters.
Procedure:
1. R.F. =drawing size/actual size (in same units) =1cm/(4x100cm) =1/400
2. Length of scale =R.F. X maximum length to be measured.Maximum length to be
measured =50m Therefore length of scale =L= (1/400) X50m
=(1/400)X50X100cm=12.5cm
3. Draw a horizontal line of length 12.5 (L).
4. Draw a rectangle of size 12.5 x 0.5cm on the horizontal line drawn above
5. Total length to be measured is 50m.therefore divide the rectangle into 5(n) equal
divisions, each division representing 10m.
6. Mark 0 at the end of the first main division.
7. From 0, number 10,20,30 and 40 at the end of subsequent main division s towards
right as shown.
8. Then sob-divide the first main division into 10 subdivisions to represent metres
(using geometricalconstruction).
9. Number the sub-divisions i.e. metres to the left of 0 as shown.
10.Write the names of main units and sub-units (METRES) below the scale. Also
mention the R.F. as shown.
11.Indicate on the scale a distance of 36metres[=3main divisions to the right side of
0+6sub-divisions to the left of 0(zero)]
S. J (GOVERNMENT POLYTECHNIC BENGALURU, ARUN KURALI LECTURER IN DEPT OF CIVIL ENGG)
PLAIN SCALES
Note: In this problem one division represents 10-metres. Each division
represents one metre.
Problem2;
Construct a plain scale of R.F.1: 50,000to show kilometers and
hectometers and long enough to measure upto 7km. Measure a distance of 54
hectometers on your scale.
1. Length of scale =(1/50,000) x7x1000x100cm=14cm
2. Draw a rectangle of size 14cmx0.3m.divide the rectangle into 7 equal divisions,
each representing 1km or 10hm.
3. Mark 0 at the end of first main division and 1,2,3…6 at the end of subsequent
main divisions towards right. Sub-divide the first division into 10 sub-divisions, each
representing 1hm.number the sub-divisions to the left of 0(zero).
S. J (GOVERNMENT POLYTECHNIC BENGALURU, ARUN KURALI LECTURER IN DEPT OF CIVIL ENGG)
Problem 3;
One square centimeter on a map represents 25 square km. draw a scale to measure a
maximum length of 75km and show 53km on the scale.
1. R.F=Drawing scale/Actual scale = 1cm2/25km2 . Here it is square km and square
centimeter take square root on both nominator and denominator
We will get R.F= 1cm/5km = 1cm/(5x1000x100cm)
So, RF = 1/500000
Now find the length of scale = RF X Maximum Measurement
= 1/500000 x (75km)
= 1/500000 x ( 75x1000x100cm)
= 75/5
Length of scale = 15cm
2. Draw a rectangle of size 15cmx0.3m.divide the rectangle into 8 equal divisions,
each representing 10km.
3. Mark 0 at the end of first main division and 10,20,30…70 at the end of subsequent
main divisions towards right. Sub-divide the first division into 10 sub-divisions, each
representing 1km.number the sub-divisions to the left of 0(zero).
4. Mark 50km on Main division and 3kms on sub-divisional scale.
53k
10
0
10
20
30
SUBDIVISION(km)
Length of scale=15cm
40
50
60
70km
MAIN DIVISION (10km)
Problem 4;
A room of 1000m3 volume is represented by a block of 125cm 3 volume. Find R.F.
and construct a plain scale to measure upto 30m.measure a distance of 18m on the
scale.
1. 125cm3 =1000m3(given) i.e. 5cm=10m. Therefore R.F =1cm/(2x100cm)=1/200
2. Length of the scale, L =1/200 x30 x 100 =15cm.
Note: while doing problems on volume /area, change the units
S. J (GOVERNMENT POLYTECHNIC BENGALURU, ARUN KURALI LECTURER IN DEPT OF CIVIL ENGG)
of volume/area into the corresponding linear measures in order
to find the length of the scale to construct the plain scale