1. Dr. R. Ribeiro, Mechanical Engg. Dept. IITD
MEL110 Graphic Science
Dimensioning
Dr. R. Ribeiro, Mechanical Engg. Dept. IITD

2. Dimensioning
BIS (Board of Indian Standards SP 46: 2003) defines dimension as a numerical value expressed in appropriate units of measurement and indicated graphically on technical drawings with lines, symbols and notes.
Units of Measurement: The most commonly used unit for length is the millimetre. In civil engineering and architectural drawing, inch or foot is often used as a unit of length. Angles are shown in degrees.
Symbols are incorporated to indicate specific geometry wherever necessary.
Notes are provided to give specification of a particular feature or to give specific information necessary during the manufacturing of the object. 2

3. Example on drawing sheet
No dimension unit to be mentioned on the drawing
At the bottom sheet mention “All dimensions in ……”
DRAWING SHEET 50
MENTION UNIVERSAL DIMENSION HERE
TITLE BLOCK
All dimensions are in mm

4. Size specification, f – symbol for diameter
Dimensioning
Providing information on a drawing about
Distances (size or functional dimensions)
Sizes and positions (location or datum dimensions) of holes, grooves and other features.
Details relating to manufacture etc.
Manufacturing detail
Location
Roughness 0.5 15
Location 15
Size, functional 30
Hole f15
Size specification, f – symbol for diameter

5. Different lines in dimensioning
Oultline - Forms the shape of the object in a view (drawn dark and continuous)
Extension line – An extension of an outline or centerline (drawn light and continuous, used to indicate the entity being dimensioned)
Dimension line – Thin continuous line terminated by arrowheads touching the outlines, extension lines or center lines (used to specify end points of a dimension)
Dimension
Extension line
Dimension line 50
Outline

6. Leader lines and notes
Leader (or pointer) line – Thin continuous line connecting a note or dimension figure with the feature to which it applies. One end of the leader terminates in an arrowhead or dot.
The arrowhead touches the outline while the dot is placed within the object or on the outline
The other end of a leader is terminated in a horizontal line underlining the note
Roughness 0.5
Leader line
Material: mild steel
Note
Leader line
Hole f15

7. Rules for leader lines > 30o
A leader line is never drawn horizontal, vertical or curved
It is drawn at an angle not less than 30o to the line that it touches
When pointing to a circle or arc, it is drawn radially
Material: mild steel
Roughness 0.5
Leader line
> 30o
Note
Hole f15

8. Arrowheads and dimension line positioning
A dimension line is placed at least 6-8 mm away from an outline and from each other
An extension line extends ~3mm beyond a dimension line
Arrowhead – Placed at each end of a dimension line, its pointed end touches an outline, extension line or a centerline. It is also placed at the end of a leader line
45o
Closed and filled
Oblique stroke
Open
Closed w
Size of the arrowhead should be proportional to the length of the dimension line 3w
~6-8mm 50
~3mm
Arrowhead

9. Systems of Dimensioning
Aligned System
In the aligned system, dimensions are aligned with the entity being measured. They are placed perpendicular to the dimension line such that they may be read from the bottom or right-hand side of the drawing sheet. Dimensions are placed at the middle and on top of the dimension lines.
Unidirectional System
In the unidirectional system, dimensions are placed in such a way that they can be read from the bottom edge of the drawing sheet. Dimensions are inserted by breaking the dimension lines at the middle. 9

10. Dimensioning systems Aligned system
(readable from bottom and right edge of sheet)
Unidirectional system
(visible from bottom edge)

11. Dimensioning elements
A line on the drawing whose length is to be shown is called an object line. The object line is essentially an outline representing the feature(s) of the object. While showing an angle, the two lines forming the angle will be the object lines.
Dimensioning is often done by a set of elements, which includes extension lines, dimension lines, leader lines, arrowheads and dimensions. These are shown in the figure below. 11

12. Placing of dimension Within extension lines Outside extension lines
With leader 7o

13. Chain (continuous) dimensioning
All the dimensions are aligned in such a way that an arrowhead of one dimension touches tip-to-tip the arrowhead of the adjacent dimension. The overall dimension is placed outside the other smaller dimensions

14. Parallel (progressive) dimensioning
All the dimensions are shown from a common reference line. Obviously, all these dimensions share a common extension line. This method is adopted when dimensions have to be established from a particular datum surface
Smaller dimensions should always be placed nearer the view. The next smaller dimension should be placed next and so on.

15. Combined dimensioning
When both the methods, i.e., chain dimensioning and parallel dimensioning are used on the same drawing, the method of dimensioning is called combined dimensioning 15

16. Circular holes
A hole is usually dimensioned by giving its diameter instead of radius. The dimension indicating a diameter should always be preceded by the symbol ø
They should be dimensioned in the view in which they appear as circles
f40

17. Cylindrical dimensions
Cylindrical features should be dimensioned by giving their diameters.
They should be dimensioned in the views in which they appear as rectangles.
CYLINDER – OUTER DIMENSION IS ALSO CIRCULAR. CAN BE HOLLOW OR SOLID

18. Number of holes with same size
When more than one hole of the same size forms a pattern, it is not necessary to dimension each one
One hole is dimensioned and a note specifies the total number of holes with that dimension
3 x f20
(or 3 HOLES, f20)

19. Dimensioning arcs
An arc is usually dimensioned by giving its radius. The dimension indicating radius should be preceded by symbol R
The R can be placed after the dimension also
The position of center of arc is denoted by a

20. ORTHOGRAPHIC PROJECTIONS19
FOR T.V. O
ORTHOGRAPHIC PROJECTIONS X Y FV O 40 10 TV 25
30 R
100
f 20
f30
FOR F.V.
PICTORIAL PRESENTATION IS GIVEN
DRAW FV AND TV OF THIS OBJECT
BY FIRST ANGLE PROJECTION METHOD
AND DIMENSION USING THE UNIDIRECTIONAL
METHOD

21. Spherical features
Spherical features may be dimensioned by giving either the radius or diameter of a sphere.
The symbols SR or Sø must precede the dimension for radius or diameter respectively.

22. Dimensioning of squares
Square features (e.g., a rod of square cross-section) are dimensioned using symbol or SQ as shown in (i) or (ii)

23. ORTHOGRAPHIC PROJECTIONS17 O
ORTHOGRAPHIC PROJECTIONS X Y 40 20
SQ30 50 60 30 10
F.V.
S.V.
FRONT VIEW
L.H.SIDE VIEW 75
FOR F.V.
FOR S.V.
PICTORIAL PRESENTATION IS GIVEN
DRAW FV AND SV OF THIS OBJECT
BY FIRST ANGLE PROJECTION METHOD AND
DIMENSION THE VIEWS USING THE ALIGNED SYSTEM

24. Dimensioning conical features
Giving 2 diameters and the perpendicular distance between them
Giving 1 of the diameters, length of taper and taper angle
Giving 1 diameter, distance between end faces and the taper (slope) using the conical taper symbol

25. Dimensioning of flat tapered features
Giving the height of one side, distance between flat ends and taper (slope) using a flat taper symbol
Giving the height of one side, length of taper and slope of the tapered face

26. Dimensioning of threads
External metric threads are dimensioned by giving the threaded length and nominal diameter preceded by symbol ‘M ’ (Fig. a)
Internal metric threads are dimensioned by giving the threaded length, depth of drilled hole before threading and nominal diameter preceded by symbol ‘M’ (Fig. b)

27. General rules of dimensioning
Between any two extension lines, there must be one and only one dimension line bearing one dimension. One of the extension lines may be common to another dimension as in parallel dimensioning.
As far as possible, all the dimensions should be placed outside the views. Inside dimensions are preferred only if they are clearer and more easily readable.
All the dimensions on a drawing must be shown using either Aligned System or Unidirectional System. The two systems should not be mixed on the same drawing.
The same unit of length should be used for all the dimensions on a drawing. The unit should not be written after each dimension, but a note mentioning the unit should be placed below the drawing.
Dimension lines should not cross each other. Dimension lines should also not cross any other lines of the object.
All dimensions must be given.
Each dimension should be given only once. No dimension should be redundant.

28. Dimensioning, correct vs. wrong25

29. Symbols and abbreviations used in Engg. drawing

30. Draw 3 orthographic views in 3rd
Draw 3 orthographic views in 3rd. Angle and dimension them using UNIDIRECTIONAL system 22
TOP VIEW
f32 24 38 57
LEFT SIDE VIEW
f12, 16 DEEP
R22 36 6 19 38 22 24 22
FRONT VIEW

31. Draw Front and R. S. views in IIIrd
Draw Front and R. S. views in IIIrd. angle with dimensions in ALIGNED system
Complete TV and dimension it for HW

32. Draw Front and R. S. views in IIIrd
Draw Front and R. S. views in IIIrd. angle with dimensions in ALIGNED system
Complete TV and dimension it for HW
Project tangent point in other view 19
f15 f9 26
f18
f28 35

33. PICTORIAL PRESENTATION IS GIVEN DRAW FV AND TV OF THIS OBJECT
ORTHOGRAPHIC PROJECTIONS
PICTORIAL PRESENTATION IS GIVEN
DRAW FV AND TV OF THIS OBJECT
BY FIRST ANGLE PROJECTION METHOD TV 10 30 50 35 FV X Y
RECT.
SLOT
30 f
60 f
20 f
FOR T.V.
Dimension using UNIDIRECTIONAL system O
FOR F.V.

34. ORTHOGRAPHIC PROJECTIONS10 15 25
S.V. O 40 25 80
F.V.
FOR F.V.
FOR S.V.
Dimension using UNIDIRECTIONAL system
PICTORIAL PRESENTATION IS GIVEN
DRAW FV AND SV OF THIS OBJECT
BY FIRST ANGLE PROJECTION METHOD