Types of Jigs and Milling Fixtures, Locating System, Clamping System, Tool Guiding and Setting sysetem

1. Rahul A. Pasale
Asst. Professor
AMGOI Vathar
Maharashtra
rhlpasale@gmail.com
+91-9823131203

2. Most common machining processes used are
• Turning
• Drilling
• Reaming
• Milling
• Boring
• Internal and External threading
When these operations are used for mass production, there is need
of toolings to reduce the operational time and enhance the production.
e.g. Machining of two holes at 40 mm center distance.

3. Jigs and Fixtures
• Jigs are used for operations like drilling, reaming, tapping, spot facing etc.
• Fixtures are used for operations like milling, boring, turning, broaching, slotting
grinding etc.
• Jigs and fixtures are used for a specific operation and for a specific job only.
Basic elements of Jigs and Fixtures:
• A locating system:
For accommodating the component at the desired place,
• A clamping system:
For holding the component firmly at the located place,
• A skeleton or body:
To contain locating and clamping elements and other elements as well
as the component.

4. Locating System
The purpose of the locating system is to receive and accommodate the
component at the specific desired place with respect to the cutting tool and
assure consistency.
e.g. As shown in fig. if
M12 hole is to be at specific position
from side AB and side AC, then the
component has to be located under the
drilling spindle to assure the position.

5. 3-2-1 Principle
The degrees of freedom of a free body are 6.
1. Linear motion parallel to
+/- X axis.
2. Linear motion parallel to
+/- Y axis.
3. Linear motion parallel to
+/- Z axis.
4. Rotational motion around X axis.
5. Rotational motion around Y axis.
6. Rotational motion around Z axis.
If a locating system is able to curtail these six degrees of freedom, it shall be
called as an ideal locating system.

6. 1. The group of 3 pads (A, B and C) restrict the freedom for linear motion
along Z axis and rotational freedom around X and Y axis.
2. The group of 2 pads (D and E) restrict the freedom for linear motion along
Y axis and rotational freedom around Z axis.
3. The single pad F restricts the remaining freedom for linear motion along X
axis.
Hence to curtail these 6 degrees of freedom optimum requirement shall be a
group of 3+2+1= 6 local surfaces.
This principle provision is known as “3-2-1 principle for location”, or
“Six point principle for location”

7. Surface Locators

8. Axis Location : Pin Locators
• Components with drilled / reamed / bored
holes are preferred pin locators.
• With clamping, it is capable of restricting
4 degrees of freedoms.
• Able to prevent the component to move
along X and Y axis and to rotate around X
and y axis.
• Larger pins having diameter like 30 mm,
35 mm…… are called as posts.
• A suitable relief is provided in order to
reduce the contacting area.

9. • The pins or posts should have their own integral resting pads offering
appropriate resting area.
• The junction of the pad and post diameter is always provided with an
undercut to avoid fouling of the sharp corners / burr at the mouth of the burred
hole.

10. Two Pin Location
• A single pin with a pad is able to
restrict five degrees of freedom except
the permission for the component of
revolve around the axis of the pin.
• Sixth degree of freedom is curtailed
by adding one more pin i.e. diamond
pin.
• When two pin locator is used, the
smaller pin is converted in to a
diamond pin. To fit the job on two
pins, when center distance between
two holes is not accurate.

11. Edge Locators
• In this case, the line contacts provided by the pin surfaces are more reliable
than the contact provided by a surface locator due to minimization of
contacting area.

12. “V” blocks location offer two parallel line contacts for cylindrical
or convex components.
V block ensures self aligning of the work piece parallel to the “V”
axis.

13. Adjustable Pin Locators
•Sometimes due to space limitations it
is prepared to insert the locating pin in
the component hole rather than
mounting the component over the pin.
• The actuation can be using rack and
pinion arrangement, cam arrangement
of compression spring.
• Adjustable locators are preferred for
heavy large size components.

14. Conical Locators
• The conical location is of self aligning type.
• Minor variations at the component size (bore) can be accepted at the location
without disturbing the alignment of component.

15. Nest Locators
• Nesting provides locating surface
from all sides of component, is
unable to move in any direction.
• e.g. connecting rods, base
bracket, flanged components with
hexagonal, octagonal flanges,
valve body ends.

16. Adjustable ‘V’ Locator
• Components like raw castings / forgings are required to be sometimes located
on their as cast/as forged circular part profiles.
• An adjustable or sliding V locator is used which accommodate the size
variation at the profile.
• The actuation can be cam operated, screw operated or rack – pinion operated.

17. Characteristics of a Good
Locating System
1. Rest pads should have their contacting area as small as possible but
strong enough against warpage and wear.
2. Locating elements should be as far as possible.
3. While locating elements like raw material of cast surface, care should
be taken to see that location bears no contact with the zones having
flash lines, fins or burrs etc.
4. To locate mutually perpendicular surfaces, locating pin diameter with
its own rest pads etc. should provide undercut reliefs to accommodate
component sharp corners / burrs.

18. Characteristics of a Good
Locating System
1. Locating elements should be visible to the operator in absence of the
workpiece.
2. Locating elements should not make loading / unloading difficult.
3. Redundency in location must be avoided.
4. Locating elements used as resting surfaces shoud be symmetrical at
the arrangement.
5. The locating system should not create accumulation of chips and
swarf.

19. Clamping System
A clamping system is supposed to hold or retain the component at
the located place.
Simple Screw Clamp
• It blocks one side of the jig /
fixture which makes loading and
unloading difficult.
• Due to direct contact with the
workpiece, it tries to rotate the
workpiece.

20. Swinging Screw Clamp
During loading and unloading the swinging clamp is switch to off
position, so it will not affect the loading and unloading of the component.
Due care is taken at the fitment of fulcrum pin to see that the pin itself
dose not come out while clamping.

21. Screw Clamp with Float Pad
By using screw clamp with floating pad, tendency of the workpiece
rotating with clamp is avoided.

22. Post Clamp
The post clamp is usable for
components carrying through, central,
precise bores.

23. Strap Clamp

24. Bridge Clamp
Bridge clamp is able to provide clamping force horizontally, when
clamping area is not available at the top surface.

25. Latch Clamp
For central vertical downward clamping force.

26. Two Way Clamp
This clamp can provide two mutually perpendicular clamping forces
in a single clamping action.

27. Equalizer Clamp
This clamp is helpful in providing two clamping force of equal
magnitude at two different points over a component.
This clamp is suitable for components with uneven surfaces exposed
for clamping.

28. Clamps Operated using Eccentric

29. Cam Clamp

30. Toggle Clamp

31. Other Clamping Aids– C Washer
For design of C washer: If the bolt / stud size is “d” mm, then
Slot width – 1.1d to 1.2d,
Outer diameter – 3.5d to 4d,
Thickness – 0.75d to 1.25 d

32. Spherical Washer
A set of Spherical washers is able to restore the surface contact and
ensure proper clamping.

33. Quick Acting Nut
This is the device which ensures quick action of the nut while clamping
and de-clamping.

34. Characteristics of Good Clamping System
1. It should secure the work piece against the influences of cutting and other
forces
2. The clamping force should not be opposite to the cutting force of self weight
of the component.
3. It should be easily accessible to the operator.
4. It should not be eccentric of offset. Clamping force should not inbalance the
component.
5. The clamping system should not dislocate the component.
6. The clamping action should not deform of deflect the component.
7. It should be simple and quick to operate.

35. Automated Clamping

36. Fool Proofing Arrangements
While locating a workpiece within a locating system, it is sometimes
the work-piece does not have a unique single orientation.
To locate workpiece at its predefined position fool proofing
arrangement is made in the jigs or fixtures.
Examples :

37. Fool Proofing Arrangements

38. Fool Proofing Arrangements

39. Design of Drilling Jigs
Drilling jigs are used for operations like drilling, tapping, reaming,
counter boring etc.
The jig contains –
1. A body or skeleton
2. A locating system
3. A clamping system
4. A system for guiding cutting tools

40. Guide Bushes
The guide bushes are cylindrical passages to guide a drill towards the
component at the desired place and in the desired direction.
The guide bush is made of high wear resistant alloy steel and case
hardened.
The plate on which bushes are fit is known as jig plate or bush plate.

41. The upper portion is known as Head
and lower one is Shank.
The tolerance on the size of the shank
O.D. and passage I.D. can be order of IT 6 or IT 7
grade.
Fundamental deviation to the bore size
is of the F type.
e.g. If drilling size 15 mm diameter, then I.D.
specification as 15.00 F 7
i.e. 15.017 / 15.035

42. Fixed Bushes
These bushes are fixed at the jig plate. The jig plate carries bore having
nominal size that of the shank of the bush.
There is interference fit between shank O.D. and bore. O.D. of the
bush shank is ground to the fundamental deviation of ‘n’ or ‘p’ type, while the
bore is of ‘H’ type.
These type of bushes are suitable for small or medium quantity.

43. Renewable Bushes
These bushes are used where the
replacement of the bushes is expected
to be frequent due to quantum of
production and relatively faster wear
and tear.
e.g. A production programme of
around 4000-5000 components/month
may required to change the bush every
after 45 to 60 days.

44. Liner is press fitted in the jig plate
where bush is press fitted in the
liner.
Liner maintained its size as H6 or
H7 fitment.
Bush maintained its size as f6 or f7
or g7 fitment.

45. Slip Bushes
The slip bushes are used for paired operations
like Drilling + Reaming or Drilling + Tapping.

46. Recommendations for Bush sizes
Particulars Size
Drill Bush I.D.
For reamed hole 1 mm less than “d” i.e. 15 mm
For tapped hole 0.8 times “d”
i.e. 16 X 0.8 = 12.8 mm ~ 13 mm
Bush O.D. (assuming 4 to 5 mm wall
thickness)
For tapping bush 16 + 8=24 mm
For drilling bush 13 + 8= 21 mm
So common bush OD is 24 mm
Shank length In the steps of 15, 20, 25 and 30 mm depends on size
of holes.
Head diameter 2.0 to 2.5 times “d”
Head thickness Around 4 to 5 mm
Liner OD (assuming 4 to 5 mm wall
thickness)
24 + 8 = 32 mm
e.g. For 16H8 reamed hole or M16 tapped hole

47. Special Bushes

48. Types of Jigs
Jigs are tailor made to suit to the specific component processing requirements.
1. Template Jig
This is the simplest type of jig; It is simply a plate made to the shape and
size of the work piece; with the require number of holes made it. It is placed on
the work piece and the hole will be made by the drill; which will be guided
through the holes in the template plate should be hardened to avoid its frequent
replacement This type of jig is suitable if only a few part are to be made.

49. 2. Box jig
When the holes are to drill more than one plane of the work piece ,
the jig has to be provided with equivalent number of bush plates. For
positioning jig on the machine table feet have to be provided opposite each
drilling bush plate. One side of the jig will be provided with a swinging leaf
for loading and unloading the work piece, such a jig would take the form of
a box.

50. 3. Leaf Jig
• Swinging jig plate is provided to accommodate the component form top,
• Locating is provided on bottom plate of the jig,
• Loaded and unloaded in vertical direction,
• The processing axis is parallel to the loading direction,

51. 4. Sandwich Jig
• Suitable for the components with through, machined bore which can be
used for location.

52. 5. Turnover Jig
• Suitable for light weight components
• Loaded / unloaded and located in vertical direction,
• Locating surface and processing surface is same

53. Types of Jigs Contd….
6. Indexing Jig
• Applicable for those components where holes more than one in
number, having symmetrical peripheral placement,

54. 7. Angular Hole Jig
• Applicable for the components with hole axis inclined to normal
component axis,

55. 8. Tumble Jig
• Applicable for small sized components with number of similar and
dissimilar holes on different sides,
9. Pot Jig
• Used for larger size external machined diameter components,
• Processing axis is parallel to the external diameter,

56. Indexing Mechanism

57. 6 basic steps of Jig design
1. Assumptions regarding earlier performed operations,
2. Selection of type of jig with justifications,
3. Selection and conceptual finalization of the location system,
4. Selection and conceptual finalization of the clamping system,
5. Designing the liner bush system,
6. Any other specific features to be adopted,

58. • Design and draw a jig for 2 holes M14 at 60 +/- 0.1 C.D. for the
component shown in figure.
1. Operations performed earlier
a. Facing of Ø 150 base
b. Facing of opposite face maintaining 70 mm dia.
c. Drilling of 16 dia. Holes at the base.

59. 2. Selection of type of jig
For this component, base is suitable for the location , so it shall be
required to be loaded/unloaded in vertical direction. The processing of the
component is at opposite side of the locating surface. Therefore a Leaf Jig is
suitable for this component.
3. Selection of locating system
The component can be given a two pin location at a any pair of
opposite holes at the base. One pin shall be cylindrical with a diameter 16f7
and clear length of 18 mm. Other pin shall be a diamond shaped.
For resting purpose 4 pads are preferred of size 30 mm dia. and 15
mm height. These pads can be placed on the same PCD, but in between a
pair of holes.

60. 4. Selection of clamping system
The clamping of work piece shall be preferred from upper side
centrally. Hence an adjustable clamping pad can be provided at the swinging
jig plate. Hence latch clamp is preferred.
5. Design of Bush / Liner system.
6. Specific Features
a) The height of the fulcrum pin shall be responsible for maintaining the
horizontally of the jig plate. So it is selected as
H = Rest pad thickness (15 mm) + Component Height (70 mm) + Chip
removal gap (10 mm) + ½ X Jig plate thickness
= 105 mm
Item I.D. O.D. Quantity
Component M 14 - 2 tapped holes
Tapping bush 14 F7 24 g6 1 slip bush
Drilling bush 12 F7 24 g6 1 slip bush
Liner 24 H7 34 p6 2 nos.
Jig plate 34 H7 - 2 bored holes

61. b. On the other side, there shall be a similar clamping post with its clamping
surface height = 15 + 70 + 10 = 95 mm
c. The clamping pad preferably softer than Mild steel, shall be adjustable to
impart required clamping pressure.
c. All items of the jig shall be of mild steel expect the liner bushes.
d. The clamping pad shall be of semicircular shape.

63. Design of Fixture
Milling fixture consists of
1. Locating system
2. Clamping system
3. Body of the fixture
4. Setting block to set the cutter
Setting Block height = H + t (without feeler gauge)
Metal Feeler strips of size available 0.1 mm, 0.25 mm, 0.5 mm, 1.0 mm etc.
Setting Block height = H + t – feeler gauge size ( with feeler gauge)

65. Design and draw a milling fixture for producing the 16 +/- 0.05 wide slot at the
component shown in the fig.
1. Operations performed earlier
a. Plain milling of the base
b. Drilling of the 12 dia. holes at the base
c. Boring of 16 +/- 0.1 dia. Hole
2. Selection of the type of fixture
a slot milling fixture to be used on a horizontal milling machine, (with a side and
face cutter with 16 mm width) can be selected for design.
3. Selection of location system
the component has to rest on its base on 4 pads of equal height 15 mm, out of 4 pads
2 opposite pads have locating pins of 12f6 size. One should be diamond pin out of
two pins.

66. 4. Selection of clamping system
two strap clamp can be provided along the 140 mm sides. Maximum height of
the stud has to be less than (Rest pads height 15 mm ) + (Slot height from component
base 45 mm) = 60 mm
5. Design of setting block
the setting block shall need two setting surfaces. The horizontal setting surface
shall be at a height of
H = Rest pad height 15 mm + Slot height 45 mm – paper feeler 0.08 mm
= 59.92 mm from fixture
The vertical setting surface shall be at a distance of
S = (0.5 X slot width 16 mm) + paper feeler 0.08
= 8.08 mm from fixture center line
For effective cutting, the required minimum cutter radius
R = slot depth 50 mm + arbor sleeve radius 20 mm + relief for component 10 mm
= 80 mm
Assuming cutter diameter 160 mm, the setting block shall be required to be 160 mm away
from nearest component edge.
6. Design of tenons
two tenons shall be required at the two colinear slots at the bottom side of the
fixture. Tenon thickness should match with the machine T slot i.e. 16 f6.