hi it engineering drawing lecture

1. Lines in Engineering Drawing

2. Types of Lines in Engineering Drawing

3. Visible lines represent features that can be seen in the
current view
Meaning of Lines
Hidden lines represent features that can not be seen in
the current view
Center line represents symmetry, path of motion, centers
of circles, axis of axisymmetrical parts
Dimension and Extension lines indicate the sizes and
location of features on a drawing

4. DIMENSIONING
Why do we need to dimension drawings?
Dimensions and notes define the size, location, finish
and other requirements to fully define what you want
manufactured.

5. Shape
Multiview
Drawing
Dimensioning
Design
a part
1. Size, Location
ENGINEERING DESIGN
2. Non-graphic information
TRANSFERRED
INFORMATION
Create
drawings
Manufacture
RESULT
Sketches
of ideas
PROCESS

6. Why is dimensioning important?
• Even if you make a drawing to scale, it would be difficult to determine
the exact precision that is needed.
• It would be time consuming to measure each of the lines to
determine measurement.
• The basis for modern part dimensioning is the need for
interchangeable parts (being able to buy something off the shelf that fits what you already have)

7. Generally, dimensioning involves identifying the size and location
dimensions.
• Size Dimensions determine the overall size and
shape of a drawing.
• Location Dimensions typically determine where
different entities are located within the drawing.

8. Location Dimensions
• When locating an item within the drawing (locating a hole or other
object) always give the horizontal and vertical position as it relates to
the object.
• Then give the size of the object
• Eg. Where is the object located and how big is it?

9. Most dimensions consist of three types of lines
• Dimension lines
• Extension lines
• Centerlines
Dimension Centerlines Extension Lines

10. Dimension Lines
• A Dimension Line is a thin, dark, solid line that is terminated by an
arrowhead.
1.0
Dimension
Dimension Line Arrow Head

11. Extension Lines
• An Extension Line is a thin, dark, solid line that extends from a point
on the drawing to which a dimension refers.
5.0
1/16 gap
Extension
Line
1/8
beyond

12. Centerlines
• A Centerline is a thin, dark line alternating long and short dashes that is
commonly used as an extension line in location holes or other symmetrical
objects.

13. Dimensioning Systems
• Unidirectional System: where all dimensions are read from the
bottom of the sheet (like a book)
• Aligned System: all the dimensions are aligned with the surface that
they represent (read from bottom or right side of sheet)

14. Dimension Stacking
• When stacking dimensions, the shortest dimension
goes closest to the object, while the longest (or
overall) appears furthest.
• Dimension Lines typically should not cross
extension lines or other dimension line
L
ABE
L THE TY
PE OF DIME
NSIONING THAT IS USE
D IN E
ACH OF THE DRAW
INGS

15. Arrow Heads
• When drawing Arrowheads they should be long and lean at a ratio of
3:1 (length:height)
• In Architecture this is different!

16. Leaders
• A Leader is a thin solid line that directs the viewer’s attention to a
note or dimension.
• A Leader with an arrow identifies a location.
• A Leader with an dot identifies a surface.
• Try not to draw leaders so that they are horizontal or vertical (and/or
to long)
• A Leader to a circle should be drawn so that it would pass through the
center of the circle if extended.
Note here Surface here

17. Dimensioning Arcs Vs. Circles
• When dimensioning an arc use the radius symbol (R)
• When dimensioning a circle use the diameter symbol ( )
R1.0
2.0

18. Over Dimensioning
• When dimensioning, it is good technique to avoid listing the
dimension more than once through out the drawing.
• If you need to list a dimension more than once, for accuracy or ease
of viewing, you must encase the dimension within a set of brackets.
(1.3753)
Reference Dimension

19. Rules and Practices
 Accurate dimensioning is one of the most demanding undertakings
when designing parts.
 Use the checklist to insure you have followed the basic dimensioning
rules.
 Keep in mind there may be a case where the need to break a standard
could occur to give clarity to the part and manufacturer.

20. Standards
 In order for the drawings to be dimensioned so
that all people can understand them, we need to
follow standards that every company in the world
must follow. Standards are created by these
organizations:
-ANSI -MIL
-ISO -DOD
-DIN -CEN
-JIS

21. Standards Institutions
 ANSI - American National Standards Institute - This
institute creates the engineering standards for
North America.
 ISO - International Organization for
Standardization - This is a world wide organization
that creates engineering standards with
approximately 100 participating countries.

22. Standards Institutions
 DIN - Deutsches Institut für Normung - The German Standards
Institute created many standards used world wide such as the
standards for camera film.
 JIS - Japanese Industrial Standard - Created after WWII for Japanese
standards.
 CEN - European Standards Organization

23. Standards Institutions
 The United States military has two organizations that develop
standards.
 DOD - Department Of Defense
 MIL - Military Standard

24. Dimensioning Checklist
 Each dimension should be written clearly with only one
way to be interpreted.
 A feature should be dimensioned only once.
 Dimension and extension lines should not cross.
 Each feature should be dimensioned.
 Dimension features or surfaces should be done to a
logical reference point.

25. Dimension Checklist
Dimension circles should have diameters
and arcs with a radius.
A center line should be extended and used
as an extension line.
Dimension features on a view should clearly
show its true shape.
Enough space should be provided to avoid
crowding and misinterpretation.

26. Dimension Checklist
Extension lines and object lines should not overlap.
Dimensions should be placed outside the part.
Center lines or marks should be used on all circles and
holes.

27. Dimensioning
Components

28. DIMENSIONING COMPONENTS
Extension lines
Dimension lines
(with arrowheads)
Leader lines
Dimension figures
Notes :
- local note
- general note
Drawn with
2H pencil
Lettered with
H pencil.

29. indicate the location on the object’s features that are dimensioned.
EXTENSION LINES

30. DIMENSION LINES
indicate the direction and extent of a dimension, and inscribe dimension figures.
10 27
43
13

31. indicate details of the feature with a local note.
LEADER LINES
10 27
43
13
10 Drill, 2 Holes
R16

32. Recommended
Practices

33. EXTENSION LINES
Leave a visible gap (≈ 1 mm) from a view and start drawing an extension line.
Extend the lines beyond the (last) dimension line 1-2 mm.
Visible gap
COMMON MISTAKE

34. Do not break the lines as they cross object lines.
COMMON MISTAKE
Continuous
EXTENSION LINES

35. Dimension lines should not be spaced too close
to each other and to the view.
11
34
Leave a space at least
2 times of a letter height.
16
35
DIMENSION LINES
Leave a space at least
1 time of a letter height.

36. DIMENSION FIGURES
The height of figures is suggested to be 2.5~3 mm.
Place the numbers at about 1 mm above dimension
line and between extension lines.
COMMON MISTAKE
11
11
34
34

37. 16.25
16.25
or
DIMENSION FIGURES
When there is not enough space for figure or
arrows, put it outside either of the extension lines.
1
Not enough space
for figures
Not enough space
for arrows
1 1

38. The JIS and ISO standards adopt the unit of
Angular dimension in degree with a symbol “o”
place behind the figures (and if necessary
minutes and seconds may be used together).
DIMENSION FIGURES : UNITS
Length dimension in millimeters without
specifying a unit symbol “mm”.

39. 1. Aligned method
2. Unidirectional method
The dimension figures are placed so that they are readable from the
bottom and right side of the drawing.
The dimension figures are placed so that they can be read from the
bottom of the drawing.
Do not use both system on the same drawing or on the same series of
drawing (JIS Z8317)
DIMENSION FIGURES : ORIENTATION

40. 30
30
30
30
EXAMPLE : Dimension of length using aligned method.

41. 30
30
30
30
30
30
30
30
EXAMPLE : Dimension of length using unidirectional method.

42. 45o
45
o
45o
45
o
EXAMPLE : Dimension of angle using aligned method.

43. 45o
45o
45o
45o
45o
45o
45o
45o
EXAMPLE : Dimension of angle using unidirectional method.

44. LOCAL NOTES
Place the notes near to the feature which they
apply, and should be placed outside the view.
Always read horizontally.
10 Drill
COMMON MISTAKE
10 Drill
≈ 10mm
10
Drill
Too far

45. Dimensioning
Practices

46. THE BASIC CONCEPT
Dimensioning is accomplished by adding size and location information
necessary to manufacture
the object.
Clear
Complete
Facilitate the
- manufacturing method
- measurement method
This information have to be

47. L
L
S
S
S
Designed
part
EXAMPLE
To manufacture this part
we need to know…
1. Width, depth and
thickness of the part.
2. Diameter and depth
of the hole.
3. Location of the holes.
“S” denotes size dimension.
“L” denotes location dimension.
S
L
L

48. ANGLE
To dimension an angle use circular dimension
line having the center at the vertex of the angle.
COMMON MISTAKE

49. ARC
Arcs are dimensioned by giving the radius, in the
views in which their true shapes appear.
The letter “R” is always lettered before the figures
to emphasize that this dimension is radius of an
arc.
or

50. ARC
The dimension figure and the arrowhead should
be inside the arc, where there is sufficient space.
R 62.5
Move figure outside
R 6.5
Move both figure
and arrow outside
Sufficient space
for both.
Sufficient space
for arrowhead only.
R 58.5
Insufficient space
for both.

51. ARC
Leader line must be radial and inclined with
an angle between 30 ~ 60 degs to the horizontal.
COMMON MISTAKE
R62.5
R62.5
R62.5
R62.5
R62.5
R62.5

52. ARC
Use the foreshortened radial dimension line,
when arc’ s center locates outside the sheet or
interfere with other views.
Drawing sheet
Method 1
Method 2

53. FILLETS AND ROUNDS
Give the radius of a typical fillet only by using a
local note.
R6.5
If all fillets and rounds are uniform in size,
dimension may be omitted, but it is necessary to
add the note “ All fillets and round are Rxx. ”
NOTE:
All fillets and round are R6.5
Drawing sheet
R12
unless otherwise specified.
NOTE:
All fillets and round are R6.5

54. The curve constructed from two or more arcs,
requires the dimensions of radii and center’s
location.
CURVE
COMMON MISTAKE
Tangent point

55. CYLINDER
Size dimensions are diameter and length.
Measurement
method
Location dimension must be located from its
center lines and should be given in circular view.

56. 
100

70
CYLINDER
Diameter should be given in a longitudinal view with the symbol “ ” placed
before the figures.

57. HOLES
Size dimensions are diameter and depth.
Location dimension must be located from its
center lines and should be given in circular view.
Measurement
method

58.  xx
Use leader line and local note to specify diameter
and hole’s depth in the circular view.
HOLES : SMALL SIZE
xx Drill, Thru.
1) Through thickness hole
 xx Thru.
or
xx Drill.
or or

59.  xx, yy Deep
HOLES : SMALL SIZE
or
xx Drill, yy Deep
Hole’s
depth
Use leader line and local note to specify diameter
and hole’s depth in the circular view.
2) Blind hole

60.  xx
Use extension and
dimension lines
Use diametral
dimension line
Use leader line
and note
HOLES : LARGE SIZE

61. COMMON MISTAKE
 xx
 xx  xx
Rxx
 xx
HOLES
 xx

62. CHAMFER
Use leader line and note to indicate linear
distance and angle of the chamfer.
S
S q
For a 45o chamfer
S S
CS
or

63. ROUNDED-END SHAPES
R12
 12
21
5
Dimensioned according to the manufacturing
method used.
Center to Center Distance

64. ROUNDED-END SHAPES
R12
21
5
12
Dimensioned according to the manufacturing
method used.
Center to Center Distance

65. ROUNDED-END SHAPES
Dimensioned according to the manufacturing
method used.
R12
21
12
16

66. ROUNDED-END SHAPES
R12
27
12
Dimensioned according to the manufacturing
method used.
Tool cutting distance

67. ROUNDED-END SHAPES
Dimensioned according to the standard sizes of
another part to be assembled or manufacturing
method used.
25
Key
(standard part)

68. ROUNDED-END SHAPES
Dimensioned according to the standard sizes of
another part to be assembled or manufacturing
method used.
20

69. Placement of
Dimensions

70. 1. Extension lines, leader lines should not cross
dimension lines.
POOR GOOD
RECOMMENDED PRACTICE

71. 2. Extension lines should be drawn from the nearest
points to be dimensioned.
POOR GOOD
RECOMMENDED PRACTICE

72. 3. Extension lines of internal feature can cross visible
lines without leaving a gap at the intersection point.
WRONG CORRECT
RECOMMENDED PRACTICE

73. 4. Do not use object line, center line, and dimension
line as an extension lines.
POOR GOOD
RECOMMENDED PRACTICE

74. POOR GOOD
5. Avoid dimensioning hidden lines.
RECOMMENDED PRACTICE

75. POOR GOOD
6. Place dimensions outside the view, unless
placing them inside improve the clarity.
RECOMMENDED PRACTICE

76. JUST OK !!! BETTER
RECOMMENDED PRACTICE
6. Place dimensions outside the view, unless
placing them inside improve the clarity.

77. 7. Apply the dimension to the view that clearly show
the shape or features of an object.
POOR GOOD
RECOMMENDED PRACTICE

78. 8. Dimension lines should be lined up and grouped
together as much as possible.
POOR GOOD
RECOMMENDED PRACTICE

79. 9. Do not repeat a dimension.
POOR GOOD
RECOMMENDED PRACTICE