jigs and fixtures.pdf

This presentation gives insight to fundamentals of Jigs and Fixture generally used in manufacturing industry

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Jigs and Fixtures
jigs and fixtures are the devices which help in increasing the rate of identical parts and reducing the
human efforts required for producing these parts, It has already been emphasized earlier that a
centre lathe is a suitable machine tool for producing individual parts of different shapes and sizes,
but for producing similar articles in great number its use will not be economical.
Against this, a capstan and turret lathe can be easily adapted for repetition work on account of the
multi-cooling arrangement and use of transverse stop this increases the rate of production.
However, every type of object cannot be machined on a capstan or turret lathe and may involve the
use of drilling, milling, planning and grinding machines, etc.
If such objects are to be produced in identical shapes and sizes on a mass scale, suitable devices
have to be used for holding and locating purposes so that the repetition work can be done. These
devices are the jigs and fixtures.
Read also: 14 Different Types of Lathe Cutting Tools.
The definitions of jigs and fixtures are given below,
Jig
A jig may be defined as a device which holds and located a workpiece and guides and controls one or
more cutting tools.
The holding of the work and guiding of the tool are such that they are located in true positions
relative to each other.
In construction, a jig comprises a plate, a structure, or box made of metal or in some cases of non-
metal having provisions for handling the components in identical positions one after the other, and
then guiding the tool incorrect positions on the work in accordance with the drawing, specification,
or operation layout.
Fixture
A fixture is a device which holds and locates a workpiece during an inspection or for a manufacturing
operation. The fixture does not guide the tool.
In construction, the fixture comprises a different standard or specially designed work holding the
device, which is clamped on the machine able to hold the work in the position. The tools are set at
the required positions on the work by using gauges or by manual adjustment.
Read also:
1. 7 Types Of Lathe Machine Chucks.
2. Grinding Machine: Types of Grinding Wheel And Grinding Machine Operation

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The main elements of jigs and fixtures:

Body: It is a plate, box or frame type structure in which the components to be machined are located.
It should be quite sturdy and rigid.
Locating elements: These elements locate the workpiece in proper position in relation to the cutting
tool.
Clamping elements: These elements firmly secure the workpiece in the located position.
Grinding and setting elements: These elements guide the cutting tool in case of jig and help in
proper tool acting in case of fixture.
Positioning elements: These elements include different types of fastening devices, which are used in
securing the jig or fixture to the machine at proper position.
Indexing elements: They are not provided always. But, many workpieces may have to be indexed to
different positions in order to perform machining operations on different surfaces or different
locations. In such cases, these elements will have to be incorporated in the jig or fixture.
Read also: Capstan and Turret Lathes
Types of Jigs and Fixtures
The quantity, type, and complexity of jigs and fixtures used to depend on the type of work to be
machined and the scale of production required, A new simple type of jigs are described below.
Types of jig
Following are the seven different types of jig.
1. Template jig
2. Plate jig
3. channel jig

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4. Diameter jig
5. Leaf jig
6. Ring jig
7. Box jig
Template Jig

The template jig is the simplest of all the types. A plate 2 having holes at the desired positions serves
as a which is fixed on component 1 to be drilled. The drill 21 is guided through these holes of the
template 2 and the required holes are drilled on the workpiece at the same relative positions with
each other as on the template. A template jig is shown in the figure.
Read Also: 16 Different Types of Milling Cutters [Complete Guide]
Plate Jig

1. A fixture holds and positions the work but does not guide the tool. Whereas a jig holds,
locates and as well as guides the tool.
2. The fixtures are heavier in construction and are bolted rigidly on the machine table.
Whereas the jigs are made lighter for quicker handling, and clamping with the table is often
unnecessary.
3. The fixtures are employed for handling work in milling, grinding, planing, or turning
operations. Whereas the jigs are used for holding work and guiding the tool particularly in
drilling, reaming or tapping operations.

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A plate jig is an improvement of the template jig by incorporating drill bushes on the template. The
plate jig is employed to drill holes on large parts maintaining accurate spacing with each other. A
plate jig is shown in the above fig.
Read Also: Milling Machine: Main Parts and It’s Working Principle
Channel Jig

The channel jig is illustrated in the fig. It is a simple type of jig having a channel-like cross-section.
The component 1 is fitted within the channel 4 and is located and clamped by rotating the knurled
knob 5. The tool is guided through the drill bush 3.
Diameter Jig

The diameter jig is shown in fig. It is used to drill radial holes on a cylindrical or spherical workpiece.
The work 1 is placed on the fixed V-block 6 and then clamped by the clamping plate 7 which is also
locate the work. The tool is guided through the drill bush 8 which is set radially with the work.
Read Also: Metal Saw Machine and Types of Sawing Machine

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Leaf Jig

The leaf jig is illustrated in the above figure. It has a leaf or a plate 13 hinged on the body at 11 and
the leaf may be swung open or closed on the work for loading or loading purposes. The work 1 is
located by the buttons 10 and is clamped by set screws 12. The drill bush 3 guides the tool.
Read Also: Broaching Machine: Types, Operations, Advantages and Broaching Methods
Ring Jig

The ring jig is shown in the above figure. It is employed to drill holes on circular flanged parts. The
work is securely clamped on the drill body and the holes are drilled by guiding the tool through drill
bushes.
Box Jig

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The box jig is illustrated in the above figure. It is of box-like construction within which the
component is located by the buttons 18. The work 1 is clamped by rotating the cam handle 19 which
also locates it. The drill bush 3 guides the tool. The box jigs are generally employed to drill a number
of holes on a component from different angles.
Read Also: Press Machine and Types of Press Machine
Types of Fixtures
Fixtures are usually named after the type of machining operation for which they are designed and
employed.
Following are the different types of fixtures:
1. Turning fixtures.
2. Milling fixtures.
3. Broaching fixtures.
4. Grinding fixtures.
5. Boring fixtures.
6. Indexing fixtures.
7. Tapping fixtures.
8. Duplex fixtures.
9. Welding fixtures.
10. Assembly fixtures.
Turning fixtures
It is quite easy-to-hold regular workpieces on lathes in standard job holding devices like chucks and
collects, between the centre and on mandrels or faceplates. But irregularly shaped components
offer a lot of difficulties in holding them correctly.

Simple odd shaped jobs can be held in chuck also, say by proper adjustment of jaws in a four-jaw
chuck or by using shaped soft jaws.
However, workpieces having complicated shaped have to be necessarily held in position with the
help of turning fixtures. These fixtures are normally mounted on the nose of the machine spindle or
on a faceplate and the workpieces held them.

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whenever necessary, the fixture may have to be provided with a counterweight or balance the
unbalance fixture. These fixtures should be carefully designed, to be rigid enough, with minimum
overhang should grip the workpieces very firmly, should not carry any dangerous projections for the
machine operator or tool or both and should be able to provide proper support to him to thin and
weak sections of the workpieces during the operation.
Read Also: The Complete List of Milling Machine Operations
Milling fixtures
These fixtures are used on milling for carrying out different milling operations on workpieces. The
fixture is properly located on the table of the machine and secured in position by means of bolts and
nuts.

The table is shifted and set in the proper position, in relation to the cutter. The workpieces are
located no the base of the fixture and clamped before starting the operation.

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Since the cutting forces involved are quite high, and also intermittent, the clamping elements.
Proper locating of the fixture on the machine table is usually achieved with the help of two tenons
provided under the fixture base. These tenons enter a T-slot of the table to provide the required
location. The fixture base can then be secured to the table by means of T-bolts and nuts.
Read Also: 6 Different types of Shaper Machine Operations
Broaching fixtures

These fixtures are used on different types of broaching machines to locate, hold and support the
workpieces during the operations, such as keyway broaching operations, such as keyway broaching,
hole broaching, etc. The use of a clamping plate as a fixture for internal pull-type hole broaching.
Grinding Fixture
Several different forms of fixtures are used in grinding machines to locate, hold and support the
workpieces during the operations. These fixtures may be the standard work-holding devices, such as
chucks, mandrels, chuck with shaped jaws, magnetic chucks, etc.
For example; a vertical surface grinder with a rotary table will normally have a rotary fixture secured
to its table. Similarly, a plain or string fixture may be provided on a surface grinder with the
reciprocating table. A drill grinding attachment is a glaring example of a standard fixture used for
grinding of drill geometry.
Whatever be the types of fixture designed for grinding operation, it should have provisions for
supply and exit of coolant, mounting of wheel dressers and should be properly balanced, if it is a
rotating fixture.
Read Also: 4 Different Types of Shaper Machine Mechanism
Boring Fixture
The operation can be performed in one of the following two ways:
 By keeping the boring bar (tool) stationary and feeding the touting workpiece on to the bar.
 By keeping the workpiece stationary and feeding the rotating boring bar into the work.

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Accordingly, therefore, the boring fixture is made in two common designs.

One of these incorporates the principle of a drilling jig, and in this, the boring bar (tool) is guided
through a pilot bush. such fixture is also often referred to as boring jigs. the other design facilitates
holding of the workpiece incorrect position, relative to the boring bar.
Although, this fixture incorporate almost all the common principles of jig and fixture design, their
construction need not be as sturdy as that of the milling fixtures, because they never have to bear as
heavy cutting loads as involved in milling fixtures, because they never have to bear as heavy cutting
loads as involved in milling operations.
Read Also: Cutting speed, Feed, Depth of cut, Machining time in lathe machine
Indexing Fixture
Several components need machining on the different surface such that their machined surface
surfaces or forms are evenly spaced.

Such components are required to be indexed equally as many as the number of surfaces to be
machined. Obviously, the holding devices (jigs or fixtures) used are made to carry a suitable indexing
mechanism. A fixture carrying such a device is known as an indexing fixture.

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Tapping Fixture
tapping fixture is specially designed to position and firmly secure identical workpieces for cutting
internal threads in drilled holes in them. Odd shaped and unbalanced components will always need
the use of such fixtures, especially when the tapping operation is to be carried out repeatedly on a
mass scale on such components.
Duplex fixtures
It is the name given to the fixture which holds two similar components simultaneously and facilitates
simultaneously machining of these components at two separate stations. While one workpiece is
machined at one station.

Both the operations according to the requirement may be similar or different. Once machining at
both the stations is over, the fixture is indexed through 180 degrees so that the first component is
shifted to the second station for the second operation and the finished component to the first
station.
The finished component is then uploaded here, replaced by a fresh component and the first
operation performed on it. The cycle goes on repeating, which enables mass production of
components at a fairly high speed.
Read Also: 14 Different Types of Lathe Cutting Tools
Welding fixtures
Welding fixtures are carefully designed to hold and support the various components to be welded in
proper locations and prevent distortions in welded structures.
For this, the locating element need to be carefully, clamping has to be light but firm, placement of
clamping elements has to be clear of the welding area. The fixture has to be quite stable and rigid to
withstand the welding stresses.
In many cases, a preferably and commonly used practice is to first tack weld the structure by holding
it in welding jig and then transfer it to a holding fixture for full welding. This helps in reducing the
chances of distortion considerably and the fixture is subjected to lesser stresses.

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Assembly fixture
The function of these fixtures is to hold different components together in their proper relative
position at the time of assembling them. For example, two or more steel plates can be held together
in relative positions and riveted.
These fixtures, which are used for holding the components for performing mechanical operations,
are known as mechanical assembly fixtures. Against this, there are other types of fixtures which the
components are held for joining, such as the welding fixtures are also assembly fixtures, but for hot
joining.
Read Also: Capstan and Turret Lathes
Advantages of employing jigs and fixtures in mass production work
The following are the advantages of jigs and fixtures in mass production work.
1. It eliminates the making out, measuring, and other setting methods before machining.
2. It increases the machining accuracy because the workpiece is automatically located and the
tool is guided without making any manual adjustment.
3. It enables the production of identical parts which are interchangeable. This facilitates the
assembly operation.
4. It increases the production capacity by enabling a number of workpieces to be machined in
the single set up, and in some cases, a number of tools may be made to operate
simultaneously. The handling time is also greatly reduced due to the quick setting and
locating of the work. The speed, feed and depth of cut for machining can be increased due
to high clamping rigidity of jigs and fixtures.
5. It reduces the operator's labour and consequent fatigue as the handling operations are
minimised and simplified.
6. It enables a semi-skilled operator to perform the operations as the setting operation of the
tool and the work is mechanised. This saves labour costs.
7. It reduces the expenditure on the quality control of the finish products.
8. It reduces the overall cost of machining by fully or partly automating the processes.
Principles of Jigs and Fixtures Design
The successful designing of a jig or a fixture depends upon the analysis of several factors which must
be carefully studied before the actual work is taken in hand. The following are the essential factors
which must be considered in designing a jig or a fixture,
1. Study of the component.
2. Study of the type and capacity of the machine.
3. Study of the locating elements.
4. Study of the loading and unloading arrangement.
5. Study of the clamping arrangement.
6. Study of the power devices for operating the clamping elements.
7. Study of the clearance required between the jig and the component.
8. Study of the indexing devices.
9. Study of the tool guiding and cutter setting elements.
10. Study of the fool-proofing arrangement.

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11. Study of the ejecting devices.
12. Study of the swarf removal arrangement.
13. Study of the rigidity and vibration problems.
14. Study of the table fixing arrangement.
15. Study of the safety devices.
16. Study of the methods of manufacturing of the jig base, body or frame.
Read Also: Slotter Machine: Types, Parts and Operations [Complete Guide]
Difference Between Jigs and Fixtures
The following are the fundamental difference between a fixture with a jig
1. A fixture holds and position the work but does not guide the tool, whereas a jig holds,
locates and as well as guide the tool.
2. The fixtures are heavier in construction and are bolted rigidly on the machine table, whereas
the jigs are made lighter for quicker handling and clamping with the table is often
unnecessary.
3. The fixtures are employed for holding work in milling, grinding, planing or turning
operations, whereas the jigs are used for holding the work and guiding the tool, particularly
in drilling reaming or tapping operations.
Read Also: Planer Machine: Parts, Types and It’s Working Principle
Advantages of Jigs and Fixtures
The advantages of jigs and fixtures are:
1. Increases the machining accuracy because the workpiece is automatically located and the
tool is guided without making any manual adjustment.
2. It increases the production capacity by enabling a number of workpieces to be machined in
the single set up and in some cases, a number of tools may be made to operate
simultaneously.
3. The handling time is also greatly reduced due to the quick setting and locating of the work.
4. The speed, feed and depth of cut for machining can be increased due to high clamping
rigidity of jigs and fixtures.
5. Enables the production of identical parts which are interchangeable. This facilitates the
assembly operation.
6. It eliminates the marking out, measuring and other setting methods before machining.
7. These devices reduce the operator's labour and consequent fatigue handling operations, are
minimized and simplified.
8. It reaches the semi-skilled operator to perform the operation as the setting operations of
the tool and the work are mechanized. This saves labour cost.
9. It reduces the expenditure on the quality control of the finished products.
10. Reduces the overall cost of machining by fully or partly automizing the processes.
Read Also:
1. Horizontal Boring Machine [Types, Tools and Operations]

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Applications of Jigs and Fixtures
Applications of jigs are:
 Drilling
 Reaming
 Tapping
Applications of fixtures are:
 Milling
 Grinding
 Planing
 Turning
 Shaping

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