Introduction to

Jigs and Fixtures

 Introduction
• The successful running of any mass production
depends upon the interchangeability to facilitate easy
assembly and reduction of unit cost. Mass production
methods demand a fast and easy method of
positioning work for accurate operations on it.
• Jigs and fixtures are production tools used to
accurately manufacture duplicate and interchangeable
parts. Jigs and fixtures are specially designed so that
large numbers of components can be machined or
assembled identically, and to ensure interchangeability
of components.
Comparison of machining cost
 JIG
• It is a work holding device that holds, supports and
locates the work piece and guides the cutting tool for a
specific operation.
• Jigs are usually fitted with hardened steel bushings for
guiding cutting tools. A jig is a type of tool used to
control the location and/or motion of another tool.
• A jig's primary purpose is to provide repeatability,
accuracy, and interchangeability in the manufacturing
of products.
• A device that does both functions (holding the work
and guiding a tool) is called a jig.
 Fixture
• It is a work holding device that holds, supports and
locates the workpiece for a specific operation but does
not guide the cutting tool.
• It provides only a reference surface or a device. What
makes a fixture unique is that each one is built to fit a
particular part or shape.
• The main purpose of a fixture is to locate and in some
cases hold a workpiece during either a machining
operation or some other industrial process.
• A jig differs from a fixture in that a it guides the tool to
its correct position in addition to locating and
supporting the workpiece.
• Examples: Vises, chucks
Jig and Fixture
 Advantages of Jigs and Fixtures
 Use of Jigs and Fixtures has the following advantages….

• It is an important aspect of workshop engineering to

produce the products in large quantities with high degree of
accuracy and inter-changeability at a competitive cost,
which can be achieved by use of Jigs and Fixtures.
• It facilitates the holding and supporting of the components,
to ensures the proper positioning of components and guide
the cutting tools.
• Reduction in machining time by eliminating or decreasing,
handling time & setting up time of components, which
increases the productivity.
 Advantages of Jigs and Fixtures
• Use of Jigs and Fixtures ensures the Uniformity of finished
products.
• It becomes possible to accommodate several components at
one setting and thus taking advantage of multiple machining.
• And it makes possible to employ unskilled or semi-skilled
machine operators to reduce operator’s labour and skill –
requirement.
• It reduces the measurement and its cost, and reduce overall
cost.
• It enhances the technological capacity of the machine tool.
• It improves the safety at work, thereby lowering the rate of
accidents.
 How do jigs and fixtures differ
Jigs Fixtures
1. It is a work holding device that holds, 1. It is a work holding device that holds,
supports and locates the workpiece and supports and locates the workpiece for a
guides the cutting tool for a specific specific operation but does not guide the
Operation. cutting tool

2. Jigs are not clamped to the drill press 2. Fixtures should be securely clamped to
table unless large diameters to be drilled the table of the machine upon which the
and there is a necessity to move the jig to work is done.
bring one each bush directly under the
drill.

3. The jigs are special tools particularly in 3. Fixtures are specific tools used
drilling, reaming, tapping and boring particularly in milling machine, shapers
operation. and slotting machine.
 How do jigs and fixtures differ
Jigs Fixtures
4. Gauge blocks are not necessary. 4. Gauge blocks may be provided for
effective handling.

5. Lighter in construction 5. Heavier in construction.

 Design considerations in Jigs & Fixtures
jigs and fixtures are comprised of several elements as indicated in Fig.
 Base and body or frame with clamping features
 Locating elements for proper positioning and orientation of the blank
 Supporting surfaces and base
 Clamping elements
 Tool guiding frame and bushes (for jig), indexing plates or systems if
necessary
 Auxiliary elements and fastening parts.
 Design considerations in Jigs & Fixtures
The design of jigs and fixtures should be simple and economical.
The principal considerations in jig and fixture design are…

i. Clamping and locating: The component should be properly

clamped and located. The method of location and clamping
should be such as to reduce the idle time to a minimum.
ii. Positioning of tool: The cutting tool should be properly
positioned relative to the component.
iii. It should be ensure that tool can be loaded and unloaded
easily.
iv. The clamp or workholder, should be strong enough to resist
the cutting forces.
v. Clamps should allow rapid loading and unloading of the
components.
 Design considerations in Jigs & Fixtures
vi. Adequate space in the form of channel ways should be
provided to enable the metal chips to be disposed easily.
vii. Adequate arrangements must be made for the supply of
coolant to the cutting edges.
viii. The equipment should be fool proof beside being safe to use.
ix. There should be safety of operation.
x. Use of minimum number of parts for making the jig or
fixture, and use of standard parts as much as possible. And
should be lighter in weight.
xi. Manufacturability i.e., ease of manufacture
xii. Durability and maintainability
 Location of Workpiece
 In the design of jig and fixtures the location of the workpiece
is very important aspect as the correct location influences
the accuracy of the finished product.
 The workpiece must be accurately located to establish a
definite relationship between the cutting tool and some
points or surfaces of the workpiece.
 The locating device should be designed such that each
successive workpiece when loaded and clamped will occupy
the same position in the work holding device.
 The locating device selected for a given work holding device
will mainly depend on nature of the work piece and
requirements of the metal removing operation.
 Basic rules for Location
 Locators should be as spaced as far apart as possible thus
using fewer locators and insuring complete contact over
the locating surface.
 Locating devices should reduce the degrees of freedom to
zero with no redundant location feature.
 Locators should be positioned to contact the work on a
machined surface.
 Locating features should have clearance provided where
necessary to clear machining burrs or chips.
 Locators provided should be fool proof.
 Principles of pin location
1. Principle of minimum locating elements:
2. Principle of mutually perpendicular planes:
3.Principle of extreme location: The locating points should
be placed as far away from one another as possible, to get
the greatest accuracy in the location of the workpiece.
 Degrees of Freedom

• A body in space have 12 degrees of freedom which is

capable of moving into space in twelve directions as shown.
 Choosing a Locating Surface
• The locating surface will be based on the geometry of
work piece and machining operation.

1. Locating from Plane surfaces

The machine table which is a flat surface will support
the workpiece with a plane surface. The machine table acts
as a reference plane.
 Choosing a Locating Surface
2. Locating from circular surfaces.
In this method also the basic reference plane for
location is the flat plane of the machine tool table
surface. V-method is used to locate round workpiece, but
V should be directed in such a way that variations in
workpiece size will not effect location.
 Choosing a Locating Surface
• V-blocks can be used both for locating and clamping a
workpiece. For this two Vees are used, one is fixed and
another one is sliding one. The fixed V acts to locate and
the sliding V acts to clamp and hold the workpiece at
one end and forces it against the fixed V at other end.
• The Vess may be provided with inclined locating
surfaces, instead of perpendicular surfaces to get the
advantage of double clamping effect.
• With inclined faces of the Vees a vertical downward
component of the clamping force is obtained in
addition to the horizontal component. The vertical
component presses the workpiece on the base of the jig
or fixture. The usual inclination of the face is 3° to 5°
Choosing a Locating Surface
 Choosing a Locating Surface
3. Locating from irregular surface.
when the dimensions of the workpiece vary from
part to part, and further if the surface is rough (casted,
forged.,), the unevenness of the irregular surface allows a
maximum of three contact points.
 General methods used for locating
• In machine tools like drilling machine, boring machine,
milling machine, planing machine, broaching machine and
surface grinding machine the job remains fixed on the bed
or work table of those machine tools.
• Fixtures are mostly used in the aforesaid machine tools
and jig specially for drilling, reaming etc. For machining in
those jigs and fixtures, the job is located in several ways
which include the followings :
1. Locating by flat surfaces
2. Locating by holes (Radial or Angular location)
3. Locating by pin and V-block
4. Locating on mandrel or plug
 General methods used for locating
1. Locating by flat surfaces
 General methods used for locating
2. Locating by holes (Radial or Angular location)
 Fig.1.Locating by two holes
 Fig.2.Locating by one hole and pin
 General methods used for locating
3. Locating by pin and V-block
 General methods used for locating
4. Locating on mandrel or plug
 Locating devices
• Locating methods and devices used depend on the
shape of the component.
• Pins or buttons are of various designs (generally round
pins) and made of hardened steel are the most
common locating devices used to locate, support or
hold the workpiece.
 Locating devices
• The shank of the pin is press fitted or driven(screw
type) into the body of the jig or fixture.
• The locating diameter of the pin is made larger than the
shank diameter to prevent it from being forced into jig
or fixture body due to weight of the workpiece or the
cutting forces.
 Locating devices
• Main difference between pin and button is in length.
Buttons are generally shorter in length than pins and
buttons are generally used for vertical location where as
pins are usually used for horizontal location. Large sizes
are referred as plugs.
• Locating buttons may be either press fit type or screwed
type. Screwed type buttons are used where wear and
tear is more and is to be replaced at quick intervals.
 Locating devices
• Depending upon the mutual relation between the
workpiece and pin, the pins may be classified as
1). Locating pins/ buttons, 2). Support pins/rest pins, 3).
Jack pins

1) Locating pins/buttons: when finely finished pre holes

are available in the workpiece, can be used for locating
purpose.
Depending upon their form, the locating pins are
classified as
(i). Cylindrical locating pins,
(ii). Conical locating pins
 Locating devices
Cylindrical locating pins: These pins are suitable when fine
finished holes are available for positioning purpose. The top
portion of these pins are provided with chamfering or rounded
corners, to facilitate the ease loading of workpiece. And these
pins may be provided with a flange.
 Locating devices
Conical locating pins: These pins are used to locate a
workpiece which is cylindrical and with or without a hole.
And any variation in the size will be easily accommodated
due to conical shape of the pin.
 Locating devices
2) Support pins (rest pins): With these pins, workpieces
with flat surfaces can be supported at convenient
points. These may be
fixed type or,
adjustable type.
 Locating devices
In fixed type of rest pins the locating surface is either
flat surface or,
curved surface
Flat headed support pins are usually employed to provide
location and support to machined surfaces, because of more
available contact area during location.
And they ensure accurate and stable location and would
not indent the workpiece.
 Locating devices
Spherical headed rest pins are conveniently used to
support rough surfaces, because these pins provide a
point support which is stable and suitable for rough
surfaces.
Adjustable type support pins are used for
workpieces whose dimensions can vary (casted, forged
etc.,)
 Locating with support pins / with out
pins...?
If the component is to be located in the jig/fixture
body, with out the use of support pins, then the surface of
the jig or fixture body has to be machined, which will
support the component. Which involves unnecessary
machining time.
Where as use of support pins save machining time,
as it is enough to arrange the machined surfaces for the
seats of the pins, instead of entire body of the fixture/jig.
However for locating a smaller workpiece where
support pins are not necessary, the fixture body is to be a
machined surface, which provide the locating surface.
 Locating with support pins / with out
pins...?
But sufficient recess should be provided so that burr on
the workpiece corners or dirt do not obstruct the proper
location of the workpiece.
 Locating devices
3) Jack pins: Jack pins or spring pins are also used to locate
the workpieces whose dimensions are subjected to variation.
In this the pins are allowed to come up under spring pressure,
and can be pressed down because of weight of workpiece.
When the location of the workpiece is secured, the pin can be
locked at that position by means of locking screw.
 Other locating devices
Profile Locators: These are used to locate workpiece from an
external profile or outside edge. These profile locators may be

i) Nesting type (cavity location), or

ii) V-locators
a). Fixed type
b). Sliding type
 Other locating devices
Diamond pin locator: A workpiece with drilled holes may
use rounnd pins for location, but any dimensional variation
between centre to centre distance of holes will cause the
workpiece to bind of round pins. Use of one round pin and one
diamond will overcome the binding.
 Other locating devices
Spherical locating plug: Use of spherical locating plugs
helps in preventing the workpieces from sticking because
of misalignment. This is because of the fact that a sphere
has only one dimension and therefore will not bind in a
hole no matter which way it is turned.
 Other locating devices
Equalising Jacks: They provide nearly equal contact
pressure between the locators. Below figure shows
mechanical equalising jack.
 Jig Bushes
Cutting tools like drills, reamers and counter boring
cutters are located and guided by jig bushes. They are fitted
into that portion of the jig known as the bush plate. Drill
bushes are hardened and ground to exact size.
They are subjected to wear because of action of chips.
Therefore consideration should be given to the necessity of
replacing the bushings in the design of jig. Drill bushes are
made of mild steel and case hardened.
Drill bushes may be classified as follows:
(i). Fixed bushes :
(a)Plain type
(b)Head type.
 Jig Bushes
1) Fixed Bushes: These bushings are pressed directly in
the jig body and are intended to remain in the jig until
they wear out.
 Jig Bushes
2) liner bushes: liner bushes are also press fitted and
are used to act as hardened guide for both renewable and
slip bushes.
Below figure shows plain type liner bush and
headed type liner bush.
 Jig Bushes
3) Renewable bush: These bushes can be replaced
easily when they get worn out. To replace the bush the
retaining screw is removed and worn bush is taken out.
 Jig Bushes
4) Slip bushes:
 They can be easily taken out of the liner bush without
opening the retaining screw.
 The head of the bush is knurled and by rotating the
head counter clockwise until the through slot coincides
with the screw head and then pulling upward the bush can
be removed.
 They are used to guide various sized tools. They are
available in several inside diameter sizes for each outside
diameter size.
 Therefore the bushing may be used, removed and a
larger inside diameter bushing may be used.
 Jig Bushes
4) Slip bushes:
 Jig Bushes
5) Screw are clamping bushes: They are used where
work piece is also to be clamped such as when alight work
piece is to be drilled. They have external threads. Due to rapid
wear of threads these bushes are not preferred for accurate
work.
 Jig Bushes
6) Special bushes: These bushes are used for special
operations such as bottom of a bushes requires shaping
to suit the profile of the component to prevent deflection
of tool as shown figure.
Clearance between workpiece and Bushing
There should be proper clearance between workpiece
and bushing to permit the removal of chips. Below figure
shows no clearance between bushing and workpiece used for
maximum precision drilling only.
Clearance (C) = 0.5 D for metals like cast iron (small chips)
= D to 1.5 D for metals like steels (long chips)
 Design principles of locating purposes

1) One or more pre machined surfaces or holes are to be

for reference from which subsequent machining will be
done. Also location must be done from the machined
surface.

2) For ease of cleaning, locating should be as small as

possible, with adequate wearing qualities.
 Design principles of locating purposes
3) Locating surfaces should not hold the swarf (which
misalign the workpiece). Proper relief should be provided
where burr or swarf will get collected.
 Design principles of locating purposes
4) Locating surfaces should be raised above surrounding
surfaces of the jig or fixture, so that chips fall or can be
swept off easily.
 Design principles of locating purposes
4) Sharp corners in the locating surfaces must be avoided.
5) Adjustable type of locators must be used for location on
rough surfaces.
6) Locating pins should be easily accessible and visible to
operator.
7) The workpiece must be supported properly, to avoid the
distortion of the wokpiece during machining.
 Clamping and Clamping devices
 If the work piece can not be restrained by the locating
devices or elements, it become necessary to clamp the
work piece in jig or fixture body.
 The most common example of clamping devices is
bench vice.
 The purpose of the clamping is to exert a pressure to
press a work piece against the locating surfaces and hold it
there in a position to the cutting forces.
 In bench vice the movable jaw of the vice exert force
on the work piece, their by holding it in correct position of
location in the fixed jaw of the vice.
 Principles of clamping purposes
 The clamping pressure should directed such that the
cutting forces should not counteract the clamping pressure.
 Clamps should never be relied upon for holding the
wokpiece against the cutting force. The cutting force be
arranged against a fixed stop or part of the fixture body.
 Principles of clamping purposes
 The movement of clamp should be strictly limited and if
possible it should be positively guided.
 Whenever possible, the lifting of clamp by hand should be
avoided if it can be done by means of a spring fitted to it.
 Clamps should always be arranged directly above the
points supporting the work, otherwise the distortion of work
can occur.
Principles of clamping purposes
 Principles of clamping purposes
 Fiber pads should be riveted to clamp faces, otherwise soft
and fragile workpieces can be damaged.
 A clamp should be designed to deliver the required
clamping force when operated by the smallest force expected.
 Clamping pressure should be directed towards the point of
support, otherwise work will tend to raise from its support.
 Clamping devices
Clamping method and system are basically of two categories :
(a) general type (without much consideration on speed
of clamping operations)
(b) quick acting types.
a).General clamping methods of common use :
1) Clamping screws: Clamping screws are used for light
clamping.
 Clamping devices
2) Hook bolt clamp: This is a simple clamping device and is
only suitable for light workpieces, where the usual type of
clamp is inconvenient.
 Clamping devices
3) Lever type clamps: The various designs in lever type
clamps are
i). Bridge clamp
ii). Heel clamp
iii). Swing strap clamp (Latch clamp)
iv). Hinged clamp
i. Bridge clamp: It is very simple and reliable clamping
device. The clamping force is applied by the spring loaded nut.
The relative position of the nut, the point of contact of
the clamp with the work and with other support should be
carefully considered, since the compressive force of the nut is
shared between the workpiece and the clamp support in the
inverse ratio of their distances from the nut.
 Clamping devices
Always x ≤ y and x should not be greater than y.
 Clamping devices
 Heel clamps: The various types of heel clamps are shown in
Fig 1.25. These consist of a robust plate or strap, centre stud and a
heel. The strap should be strengthened at the point where the hole
for the stud is cut out, by increasing the thickness around the hole.
The design [Fig. 1.25 (a)] differs from the simple bridge clamp [Fig.
1.24(a)] in that a heel is provided at the outer end of the clamp to
guide its sliding motion for loading and unloading the workpiece.
In design [Fig. 1.25(b)], the heel is solid and one piece with the
clamp. The workpiece is loaded into the jig or fixture or removed
from these, by rotating the clamp. In design [Fig. 1.25(c)], The
clamp is guided by the loose heel which is driven into the jig or
fixture body. A short stem is turned on the end of the heel which
fits loosely into a keyway in the clamp strap. The loading and
unloading of the workpiece is obtained by reciprocating the clamp
by hand. The design [Fig 1.25 (d)] is similar to that in Fig 1.25(c)
but, here the stem is provided at the end of the heel which forms
part of the jig or fixture body casting.
 Clamping devices
 Swinging strap (Latch) clamp: This is a special type of clamp
which provides a means of entry for loading and unloading the
workpieces. For this, the strap(Latch or Lid)can be swung out or in.
Two designs of swinging latch clamps are shown in Fig. 1.26.

 Hinged clamps: This clamp is similar to swinging latch lamp in

which the latch is hinged to enable the workpiece to be loaded and
unloaded. The clamp can be made integral with the latch. Fig.
1.27(a)shows a hinged clamp which is locked by means of a bolt. Fig
1.27.(b) shows a hinged clamp provided with a hook cam. This clamp
is much quicker than the bolt type and is suitable for workpieces
which maintain dimensional accuracy. The hooked end of the
operating liver acts as a cam and engages a pin. Fig 1.28 shows
some other designs of the lids or straps which may be used for
swinging latch or hinged clamps

• 4. Quick acting clamps: There are many mechanical
clamping devices(pneumatic and hydraulic devices will be
discussed later), which can be termed as quick acting.
These devices are costlier than the other types but
ultimately prove economical since these help in reducing
the total operating time. Some of the quick acting
clamping devices are discussed below:
C-clamps: The two types of C-clamps, free and captive are shown
in Fig. 1.29. To unload the workpiece, the locking nut is
unscrewed by giving it about one turn and this releases the C-
clamp. When the clamp is removed or swung away, the
workpiece can freely pass over the nut. The reverse procedure is
adopted for loading the workpiece. The free C-clamp may be
fastened to jig or fixture body to prevent it from being lost.
 Clamping devices
 Quick acting nut. This nut is shown in Fig. 1.30. 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 the nut. The use of the quick acting nut is explained in Fig. 1.31.
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 turn.
 Cam-operated clamp: These clamps find broad application and are fast and
positive in action. These should not be used where vibrations are present or
where the dimensions of the workpiece vary, e.g., sand castings. A cam operated
clamp is shown in Fig. 1.32.
 Note: No clamping devices are used if a very heavy stable job is to be
machined, whose weight is very great compared to the forces developed in the
cutting process, if these forces are in a direction that cannot disturb the setting of
the job (as, for example, in drilling holes in a heavy base plate). Clamping devices
are also unnecessary if the job is deprived of all of its degrees of freedom when it
is located into a fixture (as. for example, turning a job between centers on a
centre lathe and milling the two end pins from its two end holes, Fig. 1.9).

Clamping devices
Clamping devices
Clamping devices
Clamping devices
Clamping devices
Clamping devices
Clamping devices
Clamping devices
Clamping devices
Clamping devices
Clamping devices
Clamping devices
Clamping devices
Clamping devices
Clamping devices
A round pins or buttons are used to support or hold the
workpiece.
Main difference between pin and button is in
length. Buttons are generally shorter in length than pins
and buttons are generally used for vertical location where
as pins are usually used for horizontal location. Large sizes
are referred as plugs.
Locating buttons may be either press fit type or
screwed type. Screwed type buttons are used where wear
and tear is more and is to be replaced at quick intervals.
• • General methods of locating

• Δ Locating blanks for machining in lathes

• In lathes, where the job rotates, the blanks are located by
• ο fitting into self centering chuck
• ο fitting into 4 – independent jaw chuck and dead centre
• ο in self – centering collets
• ο in between live and dead centres
• ο by using mandrel fitted into the head stock – spindle
• ο fitting in a separate fixture which is properly clamped on a driving plate which is coaxially fitted into the lathe spindle.

– Δ Locating for machining in other than lathes

• In machine tools like drilling machine, boring machine, milling machine, planing machine, broaching machine and surface grinding machine the job
remains fixed on the bed or work table of those machine tools.
• Fixtures are mostly used in the aforesaid machine tools and jig specially for drilling, reaming etc. for batch production.
• For machining in those jigs and fixtures, the blank is located in several ways which include the followings :
• ο Locating by flat surfaces
• Fig. 8.1.8 typically shows locating jobs by their flat surfaces using various types of flat ended pins and buttons.

• Fig. 8.1.8 Locating by (a) flat surfaces and (b) types of pins used for that. (a) (b)
• Version 2
Steps usually followed in machining without
fixture:
Marking and punching
Mount and fix the blank on the machine
bed or in a vise with proper alignment
,support and clamp
Adjust the tool-work position by shifting job,
vice or tool
Initiate machining & Check/correct tool-
Work position
Complete machining
Inspection of final part
WHY GEARS ARE INTRODUCED

WHERE GEARS ARE USED

POWER TRANSMISSION
YES YOU ARE RIGHT
BUT
HOW????
•Slipping of a belt is common phenomenon
in the transmission of motion or power b/w
two shafts.
•In precision machines in which a definite
velocity ratio is of importance the only
positive drive is by means of gears or
toothed wheels
•Gear drive is provided when the distance
between the driver and follower is very
small.
 UNIT II
Unconventional Machining
Processes
Introduction, principles of
operation, equipment and
applications of AJM, USM,
WJM, EDM, ECM,CHM,
EBM, LBM and PAM
UNIT III
Press Working Tools :
Major components of a press, shear action in die
cutting operation, Blanking and Punching
operations, clearance and shear as applied to
punching / blanking operations, centre of pressure
and its calculation, scrap strip layout for blanking,
simple related problems
Types of dies - compound die, combination die,
progressive die.
Drawing die - Calculation of blank size, number of
draws, percentage
reduction, radius on punch and die, total drawing
force.
Bending die - Bending methods, spring back,
bending allowance, bending force.
UNIT - IV
Computer Aided Inspection : Types of CMM
(Coordinate Measuring Machines), CMM
construction, CMM operation and
programming, CMM software, Flexible
inspection systems, CMM applications and
benefits.
Machine vision: principle and introduction to
stages in machine vision,image acquisition and
digitization, image processing and analysis,
interpretation, machine vision applications.