Dimensioning%20

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Dimensioning Scaling

• CIVIL ENGINEERING DRAWING

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General Rules for Dimensioning

• Dimensioning should be done so completely that
  further calculation or assumption of any
  dimension or direct measurement from drawing is
  not necessary.
• Every dimension must be given but none should be
  given more than once.
• The dimension should be placed on the view where
  its use is shown more clearly.
• Dimensions should be placed outside the views.
• Mutual crossing of dimension lines and
  dimensioning between hidden lines should be
  avoided.
• Dimension line should not cross any other drawing
  of the line.
• An outline or a centre line should never be used
  as a dimension line. A centre line may be
  extended to serve as an extension line.
• Aligned system of dimensioning is recommended.

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Representation of Scales

• Scale can be expressed in the following two ways.
• Engineering Scale
• Engineering scale is represented by writing the
  relation between the dimension on the drawing and
  the corresponding actual dimension of the object
  itself. It is expressed as
• 1mm1mm
• 1mm5 m, 1mm8km
• 1mm0.2mm, 1mm5µm
• The engineering scale is usually written on the
  drawings in numerical forms.
• Graphical Scale
• Graphical scale is represented by its
  representative fraction and is captioned on the
  drawing itself. As the drawing becomes old, the
  drawing sheet may shrink and the engineering
  scale would provide inaccurate results.
• However, the scale made on the drawing sheet
  along with drawing of object will shrink in the
  same relative proportion. This will always
  provide an accurate result. It is a basic
  advantage gained by graphical representation of a
  scale.

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Representative Fraction (R.F.)

• Representative fraction is defined as the ratio
  of the length of an element of the object in the
  drawing to the corresponding actual length of the
  corresponding element of the object itself.

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Representative Fraction (R.F.)

• Example 1
• If 1 cm length of drawing represents 5m length
  of the object than in engineering scale it is
  written as 1cmcm5m and in graphical scale it is
  denoted by

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Representative Fraction (R.F.)

• Example 2
• If a 5cm long line in the drawing represents 3
  km length of a road then in engineering scale it
  is written as 1cm600m and in graphical scale it
  is denoted as

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Representative Fraction (R.F.)

• Example 3
• If a gear with a 15cm diameter in the drawing
  represents an actual gear of 6mm diameter in
  graphical scale, it is expressed by
• Scale 11 represents full size scale
• Scale 1x represents reducing scale
• Scale x1 represents enlarging scale.

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Construction of scales

• R.F. of the scale
• The maximum length of scale to be drawn on the
  drawing sheet
• The least count of the scale, i.e. minimum length
  which the scale should show and measure
• The maximum length of the scale to be drawn on
  the drawing sheet is determined by the following
  expression

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Types of Scale

• Scales are classified as
• Plain scale
• Diagonal Scale
• Comparative Scale (plain and Diagonal Type)
• Vernier Scale

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Plain Scale

• The plain scale is used to represent two
  consecutive units i.e., a unit and its
  sub-division. Example
• Meter and decimeter
• Kilometer and hectometer
• Feet and inches
• In every scale the zero should be placed at the
  end of first main division.
• From zero mark the units should be numbered to
  the right and its subdivision to the left.
• The names of the units and the subdivision should
  be stated clearly below or at the respective
  ends.
• The name of the scale or its R.F. should be
  mentioned below the scale.
• Steps
• Determine R.F. of the scale
• Determine length of the scale using the formula
  mentioned earliar
• Draw the line of the length of scale.
• Mark zero at the end of first division and
  1,2,3,4 and onward etc. at the end of each
  subsequent division to its right.
• Divide the first division into 10-15 equal
  subdivisions, each division represents the least
  count of the scale.
• Mark the units

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Plain Scale

• Exercise
• Problem 1 Construct a scale of 14 to show
  centimeters and long enough to measure upto 5
  decimeters
• Problem 2 Draw scale of 160 to show meters and
  decimeters and long enough to measure 6 meters.
• Problem 3 Construct a scale of 1.5 inches 1
  foot to show inches and long enough to measure 4
  feet
• Problem 4 Construct a scale of R.F. 1/60 to
  read yards and feet and long enough to measure
  upto 5 yards.

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Diagonal Scale

• A diagonal scale is used when very minute
  distances such as 0.1 mm etc. are to be
  accurately measured or when measurements are
  required in 3 units e.g. decimeter, centimeter
  and millimeter or yard, foot and inch.
• Small divisions of short lines are obtained by
  the principal of diagonal division
• Principle of Diagonal Scale
• To obtain the divisions of given short line A B
  in multiples of 1/10 its length e.g. 0.1AB,
  0.2AB, 0.3AB etc.
• Draw line AB
• Draw perpendicular from B to C
• Divide BC in 10 equal parts
• Number the division points 9,8,7,,1 as shown.
• Join A to C
• Through the points 1,2 etc. draw lines parallel
  to AB and cutting AC at 1,2 etc.
• Through the rules of similar triangles 11
  0.1AB, 22 0.2AB, 33 0.3AB and so on.

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Diagonal Scale

• Problem Construct a diagonal scale of R.F.
  1/4000 to show meters and long enough to measure
  upto 500 meters.
• Find the length of scale
• Draw line of length of scale and divide into 5
  equal parts. Each part will show 100 meters.
• Divide the first part into 10 equal divisions.
  Each division will show 10 meters.
• Add the left hand end, erect a perpendicular and
  on it mark equal 10 divisions of any length.
• Draw the rectangle and complete the scale as
  shown.

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Comparative Scale

• Scales having same representative fraction but
  graduated to read different units are called
  comparative scales.
• Comparative scales may be plain scales or
  diagonal scales and may be constructed separately
  or one above the other.

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Comparative Scale

• Problem on a railway map, an actual distance of
  36miles between two stations is represented by a
  10cm long line. Draw a plain scale to show a
  mile, and which is long enough to read up to 60
  miles. Also draw comparative scale attached to it
  to show a kilometer and read up to 90 km. take
  1mile1609meters
• Steps
• Calculate R.F.
• Calculate length of scale for miles and
  kilometers
• Draw plain scale for both km and miles and attach
  each other.

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Vernier Scale

• Vernier scale like diagonal scale are used to
  read to a very small unit with great accuracy. A
  vernier scale consist of two parts i) primary
  scale and ii) Vernier Scale.
• Primary scale is a plain scale fully divided
  into minor divisions.
• The graduations on the vernier are derived from
  those on the primary scale.

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GEOMETRICAL CONSTRUCTION

• CED

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GEOMETRICAL CONSTRUCTION

• BISECTING A LINE
• To bisect a given straight line
• To bisect a given arc
• TO DRAW PERPENDICULARS
• To draw a perpendicular to a given line from a
  point within it
• When the point is near the middle of the line
• When the point is near the end of the line
• To draw a perpendicular to a given line from a
  point outside it
• When the point is nearer the
• centre than the end of the line

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GEOMETRICAL CONSTRUCTION

• TO DRAW PARALLEL LINES
• To draw a line through a given point parallel to
  a given straight line
• To draw a line parallel to and at a given
  distance from a given straight line

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GEOMETRICAL CONSTRUCTION

• TO DIVIDE A LINE
• To divide a given straight line to any number of
  equal parts
• To divide straight line into unequal parts ( let
  AB be the given line to be divided into unequal
  parts say 1/6, 1/5, ¼, 1/3 and ½.)

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GEOMETRICAL CONSTRUCTION

• TO BISECT AN ANGLE
• To bisect a given angle
• To draw a line inclined to a given line at an
  angle equal to a given angle

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GEOMETRICAL CONSTRUCTION

• TO TRISECT AN ANGLE
• To trisect given right angle

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GEOMETRICAL CONSTRUCTION

• TO FIND THE CENTRE OF AN ARC
• To find the centre of given arc
• To draw an arc of a given radius, touching a
  given straight line and passing through a given
  point

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GEOMETRICAL CONSTRUCTION

• TO FIND THE CENTRE OF AN ARC (contd.)
• To draw an arc of a given radius touching two
  given straight lines at right angles to each
  other
• To draw an arc of a given radius touching two
  given straight lines which make any angle between
  them.

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GEOMETRICAL CONSTRUCTION

• TO FIND THE CENTRE OF AN ARC (contd.)
• To draw an arc of a given radius touching a given
  arc and a given straight line.
• a) Case 1
• b) Case 2

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GEOMETRICAL CONSTRUCTION

• TO FIND THE CENTRE OF AN ARC (contd.)
• To draw an arc of a given radius touching two
  given arcs
• Case 1 b) Case 2
  c) Case 3

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GEOMETRICAL CONSTRUCTION

• TO FIND THE CENTRE OF AN ARC (contd.)
• To draw an arc passing through three given points
  not in a straight line
• To draw continuous curve of circular arcs passing
  through any number of given points not in a
  straight line

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GEOMETRICAL CONSTRUCTION

• Steps
• Let A, B, C, D, and E be the given points.
• Draw lines joining A with B, B with C, C with D
  etc.
• Draw perpendicular bisectors of AB and BC
  intersecting at O.
• With O as centre and radius equal to OA, draw an
  arc ABC.
• Draw a line joining O and C.
• Draw the perpendicular bisector of CD
  intersecting OC or OC produced, at P.
• With P as centre and radius equal to PC, draw an
  arc CD.
• Repeat the same construction. Note that the
  centre of the arc is at the intersection of the
  perpendicular bisector and the line, or the
  line-produced, joining the previous centre with
  the last point of the previous arc.

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GEOMETRICAL CONSTRUCTION

• TO CONSTRUCT REGULAR POLYGON
• To construct a regular polygon, given the length
  of its side, let the number of sides of the
  polygon be seven.
• Method 1
• Inscribe Circle Method
• b) Arc Method

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GEOMETRICAL CONSTRUCTION
Method 2
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GEOMETRICAL CONSTRUCTION

• SPECIAL METHODS FOR DRAWING REGULAR POLYGONS
• To construct a pentagon, length of side given
• Method 1
  Method 2

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GEOMETRICAL CONSTRUCTION

• SPECIAL METHODS FOR DRAWING REGULAR POLYGONS.
  (contd.)
• To construct a hexagon, length of a side given
• To inscribe a regular octagon in a given square.

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GEOMETRICAL CONSTRUCTION

• TO DRAW REGULAR FIGURES USING T-SQUARE AND
  SET-SQUARES
• To describe an equilateral triangle about a given
  circle.
• To draw a square about a given circle

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GEOMETRICAL CONSTRUCTION

• TO DRAW REGULAR FIGURES USING T-SQUARE AND
  SET-SQUARES (contd.)
• To describe a regular hexagon about a given
  circle
• To describe a regular octagon about a given
  circle.

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GEOMETRICAL CONSTRUCTION

• TO DRAW TANGENTS
• To draw common tangent to two given circles of
  equal radii.
• a) External Tangents
• b) Internal Tangents

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GEOMETRICAL CONSTRUCTION

• TO DRAW TANGENTS (contd.)
• To draw common tangents to two given circles of
  unequal radii.
• a) External Tangents
• b) Internal Tangents

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GEOMETRICAL CONSTRUCTION

• LENGTH OF ARCS
• To determine length of given arc