Jigs and fixture design prof a k mansuri

Program: B Tech(Mechanical)
Class: SE
Course: Manufacturing Process-2
Unit: Jigs and fixture
Lecture 01: Design principles
School of Engineering and Technology

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www.sandipuniversity.edu.in
1. Prof Arif K Mansuri
2. Years of Experience:-24
3. Domain Expertise:-Advance Production Systems
SCHOOL OF ENGINEERING AND TECHNOLOGY

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Jigs and Fixtures

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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.

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DIFFERENCES
JIG FIXTURE
Definition Locates and Holds
the work and guides
the cutting tool in true
position of the work
Only Holds & Positions
the work, but doesn’t
guide the work
Elements Work Locating
elements, Tool
Guiding elements &
Work Clamping
elements
Work Locating elements,
Tool setting elements &
Work Clamping
elements
Construction Light Heavy
Applications Drilling, reaming ,
Tapping,
Counterboring,
Countersinking
Drill bushes used for
tool guiding
Milling, Turning,
Grinding, Broaching etc.,
Special
features
Feeler gauges, setting
blocks to adjust position
of tool in relation to work

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Uses of J & F in Manufacturing Industries
1) To reduce production cost
2) To increase production rate
3) To ensure high accuracy in part manufacture
4) To enable heavy and complicated complex shaped parts to be machined by being held rigidly to a
machine
5) To provide interchangeability
6) Reduce quality control expenses
7) Less skilled labour & save labour costs
8) Improve work safety Jigs & Fixtures are special purpose tools which are used to facilitate production
in mass scale
9) They eliminate the necessity of a special set up for each individual part
10) Once a Jig or fixture is properly set-up any number of same parts may be readily produced without
additional set-up.

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Jig
Jigs & Fixtures are special purpose tools which are used to facilitate production in mass scale
A jig also guides the cutting tool.

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Fixture
Jigs & Fixtures are special purpose tools which are used to
facilitate production in mass scale
A fixture only locates and
hold the work piece with
reference point for setting
a work piece.

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Major elements of jig and fixtures

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3-2-1 Locating Principle
⚫A workpiece, just like any free solid body, has
twelve (12) degrees of freedom
⚫To confine the workpiece accurately and
positively in another fixed body (Jig or
fixture), the movement of the workpiece in
any of the twelve degrees of freedom must
be restricted.

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⚫A workpiece, just like any free solid body, has
twelve (12) degrees of freedom
⚫To confine the workpiece accurately and
positively in another fixed body (Jig or
fixture), the movement of the workpiece in
any of the twelve degrees of freedom must
be restricted.

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• The workpiece is resting on three pins A, B
and C which are inserted in the base of
the fixed body. The workpiece cannot rotate
about the axes XX and YY and also it
cannot move downward. In this way the
five degrees of freedom 1, 2, 3, and 5
have been arrested.
• Two more pins D and E are inserted in the
fixed body, in a plane perpendicular to the
plane containing the pins A. B and
C. Now the workpiece cannot rotate about
the Z-axis and also it cannot move towards
the left. Hence, the addition of pins D and E
restrict three more degrees of freedom,
namely 6, 7 and 8.
• Another pin F in the second vertical face of the
fixed body, arrests degree of freedom 9.

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Locating Devices

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Locating Devices
-Pins of various designsand made of hardened steel are the most
common locating devices used to locate a workpiece in a jig or fixture
-The locating diameter of the pin is made larger than the shank
to prevent it from being forced into the jig or fixture body due to
the weight of the workpiece or the cutting forces.

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⚫Cylindrical Locators: Used for locating components having drilled
holes.
⚫The cylindrical component to be located is gripped by a cylindrical
locator fitted to the jig’s body and inserted in the drilled hole of the
component.
Locating Devices

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Locating Devices
⚫Conical Locator : Used for locating the workpieces having cylindrical
hole.
⚫It is superior as it has a capacity to accommodate a slight variation in the
hole diameter of the component without affecting the accuracy of
location.

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⚫Jack pin locator: Used to support rough, un-machined surface
⚫Height can be adjusted
⚫A suitable method to accommodate the components
whichare rough like castings.
Locating Devices

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Locating Devices
⚫Vee Locators: Quick and effective method of locating the
workpiece.
⚫Used for locating the circular and semi-circular type of workpieces.

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Locating Devices
workpiece.

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Locating Devices
workpiece.

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Locating Devices
• 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.

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Locating Devices
Support Pins
• With these pins (also known as rest pins),
workpieces with flat surfaces can be
supported at convenient points.

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Locating Devices
Jack Pins
• Jack pins/spring pins are also
used to locate the workpieces
whose dimensions are subject
to variation,
• The pin is allowed to come up under spring pressure or conversely is pressed
down by the workpiece. When the location of the workpiece is secured. the
pin is locked in this position by means of the locking screw

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Locating Devices
Diamond Pin Locator
⚫Diamond pinsareoften used for radial location .
⚫One cylindrical locator (Pin A) arrests five degrees of freedom, second
cylindrical locator at the position B will arrest the sixth degree of
freedom.
⚫If the two holes are identical in size then any pin can be made the
principal locator. However, if one of the holes is larger then the principal
locator will be placed in the larger hole.
⚫The second locator is made slightly smaller than the hole and relieved
from both sides to take care of the variation in the X direction. The
cylindrical surfaces will locate the part in theYdirection.

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Locating Devices
Diamond Pin Locator

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Locating Devices
Diamond Pin Locator
⚫Diamond pinsareoften used for radial location .
⚫One cylindrical locator (Pin A) arrests five degrees of freedom, second
cylindrical locator at the position B will arrest thesixth degree of freedom.
⚫If the two holes are identical in size then any pin can be made the principal
locator. However, if one of the holes is larger then the principal locator will
be placed in the larger hole.
⚫The second locator is made slightly smaller than the hole and relieved
from both sides to take care of the variation in the X direction. The
cylindrical surfaces will locate the part in theYdirection.

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Locating Devices
Diamond Pin Locator

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Locating Devices
Diamond Pin Locator
Diamond pin location is used in a fixture because
(a) It does notwearout
(b)It takes care of any variation in centre distance
between two holes
(c) It is easy toclamp the parton diamond pins
(d) It is easy to manufacture
IES – 1998, 1999

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Clamping
⚫To restrain the workpiece completely a
clamping device is required.
⚫Holds the workpiece securely in a jig or
fixture against the forces applied over it
during on operation.
⚫Device should be incorporated into the
fixture, proper clamp in a fixture directly
influence the accuracy and quality of the
work doneand productioncycle time.

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Principles of Clamping
1) The clamping pressure applied against the workpiece must counteract the
tool forces
2) The clamping pressure should not be directed towards the cutting
operation. Wherever possible it should be directed parallel to it.
3) The clamping pressure must not damage/deform the work surface.
4) Clamps should be arranged directly above the points supporting the work,
otherwise distortion of work may occur.
5) Clamping pressure should be directed towards the points of support, else
the work will tend to rise from support
6) Clamping should be simple, effective and foolproof.
7) Fibre pads should be riveted to clamp faces to avoid damage to fragile
workpieces

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Clamping
•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.
Simple Screw Clamp

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Clamping
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.

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Clamping
Strap Clamp
⚫Based upon the lever principles to amplify the
clamping force required.
⚫By tightening the stud the clamping force is
transferred to the part.
⚫Heel pin is the fulcrum about which the lever acts
while the clamping force is applied at the stud by
tightening thescrew.
⚫The actual amplification of the applied force
depends upon the distance between the stud and
the heel pin (B), and that between the stud and
thepart (A).

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Clamping
Cam Clamps
⚫ Provide clamping force because of the contour of the cam
surface that comes into contact with the plate used for the
clamping.
⚫ Plate is pushed down by the cam against the spring pressure to
hold the part in place.
⚫ Cam clamps arequick in operation.
⚫ Cam clamps are of three types, eccentric cam, flat spiral cam
and cylindrical cam.
⚫ The design shown in Fig. is flat spiral and is the most
commonlyused clamp.
⚫ A cam clamp used forquick and easy clamping a part

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Principles of Clamping

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Clamping
Cam Clamps
⚫ Provide clamping force because of the contour of the cam
surface that comes into contact with the plate used for the
clamping.
⚫ Plate is pushed down by the cam against the spring pressure to
hold the part in place.
⚫ Cam clamps arequick in operation.
⚫ Cam clamps are of three types, eccentric cam, flat spiral cam
and cylindrical cam.
⚫ The design shown in Fig. is flat spiral and is the most
commonlyused clamp.
⚫ A cam clamp used forquick and easy clamping a part

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Clamping
C-Clamps
This is quick clamping device which reduces
time required for clamping and unclamping.
To unload the work piece, the locking nut is
unscrewed by giving it about one turn and
this releases the c- clamp. When the clamp is
removed or swing away the work piece can
freely pass over the nut. Reverse procedure
is adopted for loading the work piece.

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Clamping
Quick Acting Nut
• The threads of the nut are not continuous but are interrupted.
• The length of the nut is about 2 to 3 times the thread diameter.
• The diameter of the clearance ‘D‘ is slightly bigger than the outside
diameter of the thread and the axis of the hole is inclined at angle (3° to
7°) to the axis of nut.
• When the nut is assembled over the male thread.
• It is inclined to the axis of the clearance hole.
• When the nut engages the male thread, it is dropped on to the screw threads
and is then tightly locked by giving it about half a tum.

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Clamping
Quick Acting Clamp Cam operated
• These clamps ﬁnd
application and are fast
broad
and
positive in action. These should
not be used where vibrations are
present or whore the dimensions
of the workpiece vary. e.g.. sand
castings.
ProductionTechnology Prof.

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 Design Principles for Drilling Jigs:
1. A drilling jig should be of light construction consistent with adequate
rigidity to facilitate its handling because it has to be handled
frequently during the operation.
2. A drilling jig which is not normally clamped to the machine table
should be provided with four feet.
3. The stability of a drilling jig should be as good as possible since it is
not usual to clamp it to the machine table and to ensure this, the feet
or base of the jig should extend outside the holes to be drilled.
4. Drill bushings should be fitted in fixed portion of the jig.
Drilling Jigs

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Drilling Bushes

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The stiffness of the cutting tool may be insufficient to perform certain machining operations. To
eliminate the elastic spring back in machining and to locate the tool relative to the work, use is made
of guiding parts, such as, jig bushings/templates. These must be precise, wear resistant and
changeable.
1. Press Fit bushings
2. Renewable bushes.
3. Slip Bushes
4. Screw bush.
5. Liner Bushings
1. Press Fit bushings
• These bushings are used when little importance is put on accuracy
or finish, and the tool used is a twist drill.
• Installed directly in the jig body
When the jig plate into which it is installed is thin, the flanged or headed portion increasing the length of the
bush which provides longer guiding portion to the bush than would otherwise be available. The flange or head
also acts as a stop for the tool.
Drilling Bushes

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Drilling Bushes
2. Renewable bushes
• When bushes require periodic
replacement (due to the wear of
the inside diameter of the bush,
in case of continuous or large
batch production), the
replacement is simplified by
using a renewable bush.
• These are of the flanged type and
are sliding fit into the liner bush,
which is installed (press fitted in
the jig plate).
• Must be prevented rotating or
lifting with drill by using
retaining screw.
3. Slip Renewable bushes
• Slip bushes are used when more than one bushings are to be interchanged
in a given size of the liner. ProductionTechnology Prof.Naman M.Dave

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4. Screw bushes
The screwing of the bush into the jig body not only holds the bush in place,
but it also makes the bush adjustable.
5. Linear bushes
These
known
bushings,
as
also
'master
bushings' are permanently
fixed into the jig body.
These act as guides for
renewable type bushings.
ProductionTechnology Prof.Naman M.Dave
Drilling Bushes

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Drilling Jigs: Types
1. Template Jig
2. Plate Type Jig
3. Open Type Jig
4. Swinging Leaf Jig
5. Box Type Jig
6. Channel Type Jig
7. Sandwich Jig
8. Angular Jig
9. Angle Plate Jig
10.Pot Jig
11.Turn-over Jig
12.Diameter Jig
13.Multi-station Jig
14.Standard Jig
15.Universal Jig
• Simplest type of drilling jig.
• Simply a plate made to the shape and size of the
workpiece with the required number of holes made in
it accurately.
• Placed on the workpiece and the holes in the
workpiece will be made by the drill which will be
guided through the holes in the template.
• The plate should be hardened to avoid its frequent
replacement. This type of jig is suitable if only a few
parts are to be made.

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Plate type Jig
• This is an improvement over the template type of jig. In place of simple holes,
drill bushes are provided in the plate to guide the drill. The workpiece can be
clamped to the plate and the holes drilled
Open type Jig

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Swinging leaf Jig
• A sort of open type jig in
which the top plate is
arranged to swing about a
fulcrum point so that it
completely clears the jig
for easy loading and
unloading of the
workpiece.
• The drill bushes are fitted
into the plate which is also
known as leaf, latch or lid. Video

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Channel type Jig
• Made of standard steel
channel section

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Box type Jig
• When holes are to be drilled
in more than one plane of a
workpiece, the jig has to be
provided with equivalent
number of bush plates. For
positioning the 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
workpiece. Such a jig would
take the form of a box.
• When, one or more sides of
the box jig are kept open for
loading/unloading, it is
known as Tumble type and
Trunnion type box jig.

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

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Indexing Jig
Applicable for those components where holes
more than one in number, having symmetrical
peripheral placement,

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Indexing Devices
Indexing Plate Sliding Indexing Device

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Setting Block used in Fixtures

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Types of Fixtures
Turning Fixture Simple Welding Fixture
Boring Fixture

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Principle of Fool Proofing
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 :-

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Example-1
Answer
Question –Two holes of Dia 10 to be drilled

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Answer
Question-Slot of width 10mm to be machined
Example-2

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Example-3
Answer
Question- Hole of Dia 6 mm to be drilled

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Drawing of a Jig released by Design Dept

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Drawing of a Fixture released by Design Dept

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Go to video Video

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GATE - 2005
When 3-2-1 principle is used to support and locate a
three dimensional work-piece during machining,
of degrees of freedom that are
the number
restricted is
(a) 7
(b) 8
(c) 9
(d) 10

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GATE-2013
In the 3-2-1 principleof fixture design, 3 refers to the
numberof
(a) Clampsequired
(b) Locators on the primarydatum face
(c) Degreesof freedomof theworkpiece
(d) Operationscarried out on the primarydatum face

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IES 2011
In the 3-2-1 principleof fixture 3 refers to numberof
(a) Setups possible
(b) Clamps required
(c) Positions on primary face
(d) Locating positions

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GATE - 1999
Choosethecorrectstatement:
(a)A fixture is used toguide the tool as well as to locate
and clamp theworkpiece
(b)A Jig is used toguide the tool as well as to locateand
clamp theworkpiece
(c)Jigs arc used on CNC machines to locateand clamp
theworkpieceand also toguide the tool
(d) Noarrangement toguide the tool is provided in a jig.

Jigs and fixture design prof a k mansuri

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