Design of jigs and fixtures -consist of locating and clamping principles

1. S.DHARANI KUMAR
Asst.professor
Department of Mechanical
Engineering
Sri Eshwar college of Engineering
,Coimbatore.
UNIT-1
LOCATING AND CLAMPING

2. Definitions
• Jig: A device that holds the work and
locates the path of the tool.
• Fixture: A device fixed to the
worktable of a machine and locates
the work in an exact position relative
to the cutting tool.
Superior Jig
Flexible Fixturing Systems

5. FUNDAMENTAL PRINCIPLES OF JIGS
AND FIXTURES DESIGN
LOCATING POINTS: The article to be machined must be easily inserted and
quickly taken out from the jig so that no time is wasted in placing the workpiece in
position to perform operations.
The position of workpiece should be accurate with respect to tool guiding in the
jig or setting elements in fixture.
FOOL PROOF: The design of jigs and fixtures should be such that it would not
permit the workpiece or the tool to inserted in any position other than the correct
one.

6. REDUCTION OF IDLE TIME
WEIGHT OF JIGS AND FIXTURES-It should be easy to handle, smaller in size
and low cost in regard to amount of material used without sacrificing rigidity and
stiffness.
JIGS PROVIDED WITH FEET: Jigs sometimes are provided with feet so that it
can be placed on the table of the machine.
MATERIALS FOR JIGS AND FIXTURES:
CLAMPING DEVICE: It should be as simple as possible without sacrificing
effectiveness. The strength of clamp should be such that not only to hold the
workpiece firmly in place but also to take the strain of the cutting tool without
springing when designing the jigs and fixtures.

7. ESSENTIAL FEATURES OF JIGS AND FIXTURES
 Reduction of idle time – Should enable easy clamping and unloading such that idle
time is minimum.
Cleanliness of machining process – Design must be such that not much time is
wasted in cleaning of scarfs, burrs, chips etc.
Replaceable part or standardization – The locating and supporting surfaces as far as
possible should be replaceable, should be standardized so that their interchangeable
manufacture is possible.
Provision for coolant – Provision should be there so that the tool is cooled and the
swarfs and chips are washed away.

8. Hardened surfaces – All locating and supporting surfaces should be
hardened materials as far as conditions permit so that they are not quickly
worn out and accuracy is retained.
Inserts and pads – Should always be riveted to those faces of the clamps
which will come in contact with finished surfaces of the work piece so that
they are not spoilt.
Fool-proofing – Pins and other devices of simple nature incorporated in
such a position that they will always spoil the placement of the component
or hinder the fitting of the cutting tool until the latter are in correct position.

9. Economic soundness – Equipment should be economically sound, cost of design
and manufacture should be in proportion to the quantity and price of producer.
 Easy manipulation – It should be as light in weight as possible and easy to
handle so that workman is not subjected to fatigue, should be provided with
adequate lift aids.
Initial location – Should be ensured that work piece is not located on more than
3 points in anyone plane test to avoid rocking, spring loading should be done.
 Position of clamps – Clamping should occur directly above the points
supporting the work piece to avoid distortion and springing.

10. Clearance – Sufficient amount of clearance should be provided around the
work so that operator’s hands can easily enter the body for placing the
work piece and any variations of work can be accommodated.
Ejecting devices – Proper ejecting devices should be incorporated in the
body to push the work piece out after operation.
Rigidity and stability – It should remain perfectly rigid and stable during
operation. Provision should be made for proper positioning and rigidly
holding the jigs and fixtures.
Safety – The design should assure perfect safety of the operator.

11. LOCATING PRINCIPLES
Location of the component is very important aspect to influence the
accuracy of the finished product.
 The each successive work piece when loaded and clamped will occupy
the same position in the jig or fixture.
 Work holding device mainly depends on the nature of work piece and
requirement of the machining operation.

12. Principles of location
Principles of Six point Location
Principle of least point
Principle of Extreme positions
Principle of mutually perpendicular planes
Principle of fool proofing
Redundant Locators

14. Six point Location Principles
Pin 1,2 and 3
for z-z axis translation
y-y axis rotation
x-x axis rotation
Pin 4 and 5
for y-y axis translation
z-z axis rotation
Pin 6
for x-x translation

16. 3-2-1 Principle
FIGURE 27-4 Workpiece location is based on the 3-2-1 principle. Three points will define a
base surface, two points in a vertical plane will establish an end reference, and one point
in a third plane will positively locate most parts.

17. Principle of fool proofing

18. Principle of mutually perpendicular planes
•The "3-2-1" principle can
also be put as a work piece
may be fully located by
supporting it against three
points in one plane, two
points in second plane and
one point in a third plane.
• These three planes are not
parallel and are preferably
perpendicular to one another.
• If the locating surfaces are
not perpendicular to one
another, the difficulties will
arise

19. LOCATING METHODS AND DEVICES
Locators are those parts of a jigs or fixture which helps a work piece to
seat in proper position in it .
Depend upon type of work, locators are designed .
The various locating devices and methods are shown in next.

20. PIN AND BUTTON LOCATORS
Button is used to support the job firmly and holds it in position.
Only difference between pins and buttons is length .
The length of the buttons smaller than pins.
Buttons generally used for vertical locations.
Pins generally used for horizontal locations.

22. DIFFERENT TYPE OF PINS USED FOR LOCATING
1. Cylindrical locating pins
2. Conical locating pins
3. Supporting pins or flat locators
4. Adjustable pin locator
5. Jack pin locator
6. Diamond pin locators

23. • Cylindrical pin used to locate a work
piece from a hole produced by
previous operation.
• The locating diameter of the pin is
made a push fit with the hole in the
work piece.
• The top portion of theses pins is given
a sufficient lead by chamfering.
1. Cylindrical locating pins

24. 2.Conical locating pins
• Locators are proffered over the
cylindrical locators where it is
necessary to accommodate
variation in the diameter of the
work piece with out affecting the
accuracy location .

25. Exercise 4-4
• Determine the basic size and type of fit given the limits for the shaft
and hole.
Shaft Limits Hole Limits Basic
Size
Type of fit
1.498 - 1.500 1.503 - 1.505
.751 - .755 .747 - .750
.373 - .378 .371 - .375
.247 - .250 .250 - .255
1.5 Clearance
.75 Interference
.375 Transition
.25 Line

26. 3.Supporting pins or flat locators
Supporting work piece by supporting pins from a flat surface .
Pins are fitted into the jigs or fixture body with interference fit.

27. 3.Adjustable pin locator
Adjustable pin locators are used when the surface is rough or uneven, such
as in castings ,forgings or non machined surfaces.
Lock nut
Jig
body
Adjustable
knob

28. Prepared Compression Die
Bottom Die plate Top Punch Plate
Height Adjustment Pin
1/8/2015 28

29. 4.Diamond pin locators

31. 6.V -Locator
V-locators are widely used for locating cylindrical surfaces from
outside .
V-locators are classified in two types
1.Fixed V-locator
2.Adjustable type V-locators
(a)Cam –operated adjustable type V-locator

32. 1.Fixed V-locator

33. 1.Fixed V-locator

34. 2.Adjustable Type V-locator
The sliding Vee block may be actuated by means of a hand
operated screw.

35. 7.Bush Locators
• Shaft type work pieces can be
easily locate in a hardened steel
bushes.
• The bushes can be plain or
flanged type.

36. Nest or cavity Locators

40. Principles of Clamping
1. It is used to hold the work piece in the correct relative position .
2. The clamping pressure must only hold the work piece and should never be
great enough so as to damage, deform or change any dimensions of the work
piece.
3.The clamping and cutting forces should be directed towards the locating
pins, otherwise the work piece may get bent or forced away from the locating
pins during machining.

41. 4. Clamping should be simple, quick and foolproof. Complicated clamps
lose their effectiveness as they wear.
5.The movement of a clamp should be strictly limited and if possible it
should be positively guided.
6.Whenever possible, the lifting of the clamp by hand should be avoided if
it can be done by means of a spring fitted to it.

42. 7.The clamps should always be arranged directly above the points supporting
the work, otherwise the distortion of the work can occur.
8.Fiber pads should be riveted to the clamp faces, otherwise soft and fragile
work piece can get damaged.
9.Clamping pressure should be directed towards the points of support,
otherwise work will tend to rise from its support.
10. The clamps should always be arranged directly above the points supporting
the work, otherwise the distortion of the work can occur.

43. Clamping pressure

44. Clamping pressure

45. Position of Clamping

46. Distortion During Clamping

47. Clamping Examples

48. Clamping Devices
1.Mechanical actuating clamps
1. Screw clamps
2. Lever clamp or Strap clamp
• Bridge clamp
• Heel clamp
• Edge clamp
3.Latch clamps
4.Hinged clamps
5. C-clamps
6.Cam operated clamps
7.Wedge clamp
8.Quick acting nut
9.Toggle clamps
10.Bayonet clamp
11.Hook bolt clamp
12.Equalizing clamp

49. 1.Screw clamp

51. 2.Lever clamp or Strap clamp

52. a. Bridge clamp

53. b. Heel clamp

54. c.Sliding heel clamp
Clamping movement
Keyway

55. solid heel clamp

56. e. Edge clamp

57. 3.Swinging latch clamp

59. 4. Hinged clamps

60. a. Cam-operated clamp

61. c. Two way hinged clamp

62. 5.Free ‘C’ clamp

63. a. Captive C-clamp

64. 6.Cam actuated plate clamp

65. 7. Wedge clamp

66. 8.Quick acting nut

67. 9.C-frame type toggle clamp

68. A.Pusher type toggle clamp

69. 11. Bayonet clamp

70. 12. Hook clamp

71. 13.Equalising clamp

72. 14.Hydraulic clamping

73. 15.Air to hydraulic booster

74. Parts of Jigs and Fixture
• Base
• Buttons
• Pins
• Handles and knobs
• Lifting ring
• Stock section
• Press fit Bushes
• Renewable Bushes
• Slip Bushes
• Linear Bushes
• Threaded Fasteners

75. Parts of Jigs and Fixture
• Base
• Buttons
• Pins
• Handles and knobs
• Lifting ring
• Stock section
• Press fit Bushes
• Renewable Bushes
• Slip Bushes
• Linear Bushes
• Threaded Fasteners

76. Base

77. Buttons

78. Pins

79. Handles and knobs

80. Lifting ring

81. Stock section

82. Press fit Bushes

83. Renewable Bushes

84. Slip Bushes

85. Linear Bushes

86. Threaded Fasteners