Everything You Need to Know About Jigs and Fixtures

DIFFERENT TYPES OF JIGS
AND FIXTURES

INTRODUCTION
 Jig and Fixture are production work holding
devices used to manufacture duplicate parts
accurately.
 They are special purpose tools used for large
scale production by semi skilled operator.
 They can also be used for small scale
production when interchangeability is important
by skilled machinist when the workpiece is
difficult to hold without special equipment.

INTRODUCTION
They are used in industry:
 To reduce cost of production
 To increase productivity
 To assure accuracy of component
 For mass production of component on its
repeatability basis
 For fully or partial automation of work
 To increase the versatility of the machine tool
 improve quality with greater machining accuracy

INTRODUCTION
 Jigs and fixtures are so closely related that the
terms are sometimes confused or used
interchangeably.
 The difference is in the way the tool is guided to
the work piece.
 Fixture locates, holds and supports the work
securely so the required machining operation
can be performed
 Jig not only locates and supports the workpiece
but also guides the cutting tool

• The main construction difference between a jig
and a fixture is mass
• Because of the increased tool forces , fixtures
are built stronger and heavier than a jig would
be for the same part
• They are made basically the same way as far
as locators and positioners are concerned
INTRODUCTION

INTRODUCTION
• The term jig should be used only for devices
employed while drilling, reaming or tapping holes
• It is not fastened to the machined on which it is
used
• So it may be moved around on the table of the
drilling machine to bring each bushing under the
drill
• It is not fastened to the drill press table for small
w.p, however holes above 0.25 mm inch in
diameter are to be drilled, it is usually necessary to
fasten the jig to the table securely.

INTRODUCTION
• Jigs make it possible to drill, ream and tap
holes at much greater speeds and with
greater accuracy
• Skilled workers are not required
• Responsibility for the accuracy of hole
location is taken from the operator and given
to the jig
• Jigs physically limit and control the path of
the cutting tool with the help of bushings

INTRODUCTION
• For machining operations like milling,
shaping, turning, broaching, etc., the term
fixture should be used
• A fixture hold and locates the work during
machining but does not contain special
arrangements for guiding the cutting tools
• A fixture is also fixed to the machine
• The accuracy of machining depends upon
the operator and construction of machine
tool

TYPES OF DRILL JIGS
• Open Jigs:
Used for simple operations
Work is done only on one side of the part
• Closed or Box Jigs:
Used for parts that must be machined on
more than one side

Operations Common to a Drill Jig

TEMPLATE JIGS
 It is the form of jig consisting of a suitable material having
holes for correct location
 The plate serve as a template which is fixed on the
component to be drilled
 Temple jigs are normally used for accuracy rather than
speed.
 Used for locating hole pattern on large workpieces
 Usually not clamped (self-clamping)
 It is the least expensive
 Simplest type of jigs
 They may or may not have bushings. When the bushings
are not used, the whole jig plate is normally hardened.

PLATE JIGS
 It is the modified form of the template jig
with jig bushes incorporated on the temple
 Consist of a single bush plate with a
provision for locating and clamping of w.p.
 They have built-in clamps to hold the work
 They use a flat plate containing bushing
as their main structural member
 All the details are attached and referenced
to this plate
 May or may not have legs

PLATE JIGS
• Easy part loading and unloading, chip removal by
providing clearance b/w plate and the w.p.
• Also called open jig
• Slip bushings for operations other than drilling
• Thin parts stacked for drilling several parts at one time
• These jigs are sometimes made with legs to raise the jig
off the table for large work.
• This style is called a table jig
• The feet provide square resting surface to the jig.
• The diameter of the jig feet should be bigger than the
slot of machining table to prevent the feet from falling
into the slots.

SANDWICH JIGS
 A form of plate jig with a back plate
 The w.p is clamped like a sandwich b/w
the base plate and the jig plate.
 This type of jig is ideal for thin or soft parts
that could bend or wrap in another style of
jig.
 Here, the use of bushings is determined
by the number of parts to be made and
diameter of the hole.

ANGLE-PLATE JIGS
• Used to machine parts at right angles to
their locators
• Pulleys and Gears use this type of jig

MODIFIED ANGLE-PLATE JIG
 which is used for machining angles
other than 90 degrees.
 Both of these examples have clearance
problems with the cutting tool.

BOX JIGS
• Surround the part totally
• Shape resembles a box
• In the figure, for loading, the cam rod is taken
out of the jig and the w.p placed in position
inside the jig
• The cam rod is then replaced and rotated to its
locking position
• This holds the work-piece firmly so that the
drilling operation can be performed
• Such jigs are generally used for components
having irregular shapes or that cannot be held
by common methods.

BOX JIGS
• Number of holes can be drilled
economically with box jig.
• One side is open for loading and
unloading the w.p and provided bushing
arrangements.
• The box jig can permits drilling of holes in
three sides of the work-piece and saves
times and increase production.

Trunnion Jig
• Jig is constructed like a box with jig bushes on
various sides.
• It is generally used for large and odd shaped
parts.
• The jig is well suited for large, heavy parts that
must be machined with several separate plate
type jig.
• Due to large size and weight of the workpiece
and the jig, it is not possible to move jig
manually for drilling the hole on the various
sides.

CHANNEL JIGS
• The work-piece is mounted against the top and
one side of the jig
• It is clamped from the third side
• It’s a type of box jig
• Provides better stability and support for work-
piece
• This type is limited to work-pieces of simple
symmetrical shapes
• It mainly consist of the jig body, jig bush and
screws and w.p is clamped inside the channel
with the help of screw.

LEAF JIGS
• They are similar to box jigs, but main differences
are size and part location.
• Distinguished by their hinged cover, or leaf
• Leaf carrying the bushing can be swung open to
load and unload quickly
• Suitable for complicated workpieces with irregular
contours
• Equipped with a handle for easy movement
• It consist of drill bush, hinge pin, set screw leaf
• Chips may accumulate inside and cause trouble

INDEXING JIGS
 Many components require holes at stated
angular positions.
 Used to drill a series of holes in a circle on the
face of a work-piece under a single bushing
 Brings the hole portion under the drill each time
it is indexed
 To do this a reference plate and a plunger is
used
 For this purpose multi head machine is used at
regular intervals.
 The operation can also be performed on single
spindle machine

PUMP or UNIVERSAL JIGS
• They are similar version of sandwich jig.
• Produced commercially as basic units and are
adapted to specific jobs by tool makers
• The lever activated plate makes this tool very
fast to load and unload
• Rigid, low weight, ample chip clearance and
ease of operation
• Handle connected to a cam or rack to clamp
workpiece
• It is also known as universal jig used for any
given part by adding the necessary locators and
bushes.

PUMP or UNIVERSAL JIGS
• The guide pillars attached to the jig plate have
rack gear teeth on one side.
• Purpose of gear meshing by rotating the handle
is to raise or lower the rack pillar with the jig
plate.
• Pump jigs are suitable for drilling only a single
hole on a fixed spindle drilling machine.
• One pump can be used for number of
workpieces by providing detachable jig plate and
base plate for different workpieces..

MULTISTATION JIGS
 Commonly used on multi-spindle machines
 Facilitates more than one workpieces at a time
 For example one part being drilled, another can
be reamed and third counter-bored
 The final station is used for unloading the finished
part and loading fresh part
 It is the complex and specialized type of the jig
that cannot be further classified and skilled
worker is required to operate,

V-BLOCK JIGS
• Used to drilling radial holes in cylindrical or
spherical workpiece.
• It mainly consist of the V-block clamping plate.
• The component is placed on the V-block and
clamped rigidly by means of a clamping plate
and bolt.

V-BLOCK JIGS
• These jigs may also be called diameter
jigs by some toolmakers.

VISE JIGS
• Constructed by attaching special inserts to the
jaws of a regular machine vise
• Generally used for low volume and short
production runs.
• It is generally used for drilling the shafts and
consists of a pair of specially designed jaws,
setting stops and support.

GENERAL CONSIDERATIONS IN
THE DESIGN OF DRILL JIGS
Rigidity:
• Jig must be strong enough to withstand all forces
applied to it
• It must also resist deflections that may be the result
of excessive tightening of clamps that hold the w.p
in place
• The work must also be supported so that it does
not bend under drilling pressure
• Cast iron is generally used because it absorb
shocks and compressive forces.

 The type of machine in which operation is
performed needs careful considerations
 The layout of the jig must provide adequate
hand clearance for easily loading and unloading
and process for loading and unloading must be
quick
 Errors arise in components due to wear, dirt,
chips burns and wear resistance surfaces
should be small and easily replaceable.
 Bushes are provided on a jig for guiding drills,
reamers and borings, for the desired positioning

 To increase tool life and keep the components
cool, a coolant is provided in cutting edge in
sufficient quantity.
 Design considerations require easy ejection of
the component from jig (particularly for heavy
ones) to save the operation time and increase
the productivity, pneumatic devices are very
suitable for easy and quick ejection.

Chip Control:
• Types of chips: segmental and continuous
• The segmental chip is preferred
• Space between the work and bottom of drill
bushings to allow chips to pass b/w the work
and busing plate (1- 11/2 times dia. of drill)
• Three ways of chip removal: coolant,
manually with brush or hook, compressed air

Jig feet and legs:
• A drill jig should stand on four feet (Or legs)
rather than a flat surface
• Jig feet may be built into the jig body or purchased as
standard parts
• They are usually placed on the extremities of the jig
• Feet should be ground so that they are all in one
plane after they are mounted on the jig base
• When jig is bolted to machine table, usually provides
with four feet instead of a flat bottom, squaring
provides easily chip removal and sustainability.

Miscellaneous considerations:
• Sharp corners should be eliminated
• Provisions should be made for the coolant to get
to the drill
• Holes or passages for escape of the coolant
• Gripping surfaces should be knurled
• The jig should be large enough to hold it against
the torque of the drilling machine
• It must be easy to handle

METHODS OF CONSTRUCTION
• Generally jigs are constructed by holding the
components together mechanically
• This is referred to as built-up construction
• Adv.: All parts can be completely machined before
assembly and worn parts can be easily replaced
• Minor adjustments can be made during assembly
• Jigs of this type are held together by socket-head
cap screws and dowels
• Screw serve to hold the components together while
the dowels serve to hold the parts in alignment

METHODS OF CONSTRUCTION
• Welded construction is also used in
building a drill jig
• Drill jigs are sometimes constructed by a
combination of welding and mechanical
assembly
• The main body may be of welded
construction with the smaller components
attached by screws and dowels
• The main body of a drill jig may also be
cast

Materials for Jigs and fixtures
Following points for selection:
 Easily available
 Ability to withstand the stress expected in service
 Ability to retain its shape and size
 Corrosion resistance
 Cast iron is generally used as materials for jig and
fixture, light materials like brass, bronze, steels,
plastic can also be used.
 The choice of the proper material can also be
selected when the operating conditions are known.

FIXTURES
• Used to hold workpiece during machining
• Fixture is always fixed to the m/c table
• Classified by the type of machine on which
they are used

VISE FIXTURES
• Sometimes standard m/c vises are adapted
with special jaws
• Special jaws are designed for workpieces
with irregular contours
• Used with various types of m/c tools

MILLING FIXTURES
• Used to hold the w.piece in correct relation
to the cutter
• Attached to m/c table with T-slots
PARTS OF MILLING FIXTURE:
(1) Base (2) Clamps (3) Rest Blocks
(4) Locating Points (5) Gaging Surfaces

BASE:
• Consists of base plate with flat & accurate under
surface
• Various components are mounted on it
• It mates with the surface of milling m/c table
• Used as reference plane
• Has slots to clamp fixture to the table
• It has a keyway running lengthwise in the base for
two keys used to align the fixture on the milling
machine table
• The keys are pressed into the keyway at both
ends of the fixture and held there by socket-head
cap screws

BASE:
• The fixture is attached to the milling-
machine table and held in alignment by
two keys attached to the fixture base
• These keys fit very closely into the T slot
of the mill table
• The fixture is held firmly to the table by T
bolts or hold-down clamps

Underside of Mill-fixture Base

• The type of milling machine
• Dimensions of T slots
• The center-to-center distance of T slots
• The dimensions of the milling machine table
• The length of table travel in all three feed
movements
The center-to-center distance of T slots varies
from machine to machine
If the fixture is to be used on more than one
machine, it may be well to hold the fixture with
strap clamps
Data required before starting the
design of a milling fixture

Strap Clamp Holding Fixture to
Machine Table

Effect of Cutting Forces on
Workpiece at Beginning of Cut
• Cutting forces exerted by a milling cutter
change as the cutter leaves or enters the
work and throw an extra load on clamps
• Clamps must not loosen by vibration
caused by interrupted cutting of mill cutter
• Interrupted cutting occurs at the beginning
and end of the cut

Effect of Cutting Forces on
Workpiece at Beginning of Cut
(a) Conventional milling: work is lifted up at
beginning of cut
(b) Climb milling: work is forced down at one
end but lifted up at the other

Accuracy of Contact Between
Bearing Surface and Workpiece
• A feeler gage of predetermined thickness
is inserted between the bearing surface
and the workpiece resting upon it
• Bearing surfaces are usually in the form of
pins, pads and plates

Use of Setting Gages to Locate Mill
Fixture in Correct Relationship to Cutter

TYPES OF MILLING FIXTURES
• Milling Fixtures can be classified in a
variety of ways:
(1) According to the way the workpiece is
clamped, such as hand-clamping fixtures,
power-clamping fixtures, toggle fixtures
etc.
(2) According to the way the workpiece is
located, such as center fixtures, V-block
fixtures etc.

(3) According to the method of presenting the
workpiece to the cutter, as rotary fixtures
where the workpiece is rotated under the
cutter. Indexing fixtures where the workpiece
is indexed into the next position during the
machining cycle.
(4) According to the milling operation performed
on work, such as face-milling fixtures, slab-
milling fixtures, slotting fixtures, string-milling
fixtures etc.
TYPES OF MILLING FIXTURES

MILLING FIXTURES
STRING or LINE MILLING FIXTURES:
• A number of components strung behind each other in
a line
• The fixture moves relative to the cutters

MILLING FIXTURES
HYDRAULIC CLAMPING FIXTURE:

MILLING FIXTURES
SPRING TYPE FIXTURE:

MILLING FIXTURES
CLAMP TYPE FIXTURE:

MILLING FIXTURES
VACUUM FIXTURE:
• It’s a suction holding device
• Used where holding without distortion is
vital
• Uses a vacuum pump
• Part acted upon by atm. Pressure
• It exerts a downward force on all sides
exposed to vacuum

BROACHING FIXTURES
• A broach is a series of progressively taller
chisel points mounted on a single piece of
steel
• Use of a broach is to cut splines or a
square keyway on objects such as gears,
driveshafts, pulleys etc.

GRINDING FIXTURES (Magnetic
chucking devices)
• Workpiece can be quickly mounted &
removed
• Distortion caused by mechanical clamping
eliminated
• Mild steel plates separated by nonferrous
ones
• Magnetic flux passes from magnetic chuck
through steel plates and workpiece

GRINDING FIXTURES (use of
magnetic chuck parallels)

GRINDING FIXTURES (use of
magnetic-chuck V block)

LATHE FIXTURES
Three-jaw Universal Chucks:
• Three-jaw chucks used for circular and
hexagonal work
• Three-jaw chucks are usually self-centering
• Three jaws move simultaneously when
adjusted
• This simultaneous movement is caused by a
scroll plate into which all three jaws fit
• They are usually provided with two set of jaws,
one for outside chucking and the other for
inside chucking

LATHE FIXTURES
Four-jaw Independent Chucks:
• 4-jaw chucks are usually non-self-centering
• Each jaw can be moved independently
• Ideal for gripping round, square, hexagonal and
irregularly shaped workpieces
• The jaws can be reversed to hold work by
inside diameter
• Multi-jaw chucks (6 or 8 jaws) for special
purpose and high standards of accuracy

LATHE FIXTURES
Magnetic Chuck:
• It has the advantage of holding iron or steel
parts
• The parts that are too thin or that may be
damaged if held in a conventional chuck
• Suitable only for light operations
• A magnetic chuck consists of an accurately
centered permanent magnet face

LATHE FIXTURES
Faceplates:
• Circular metal plate fixed to the end of spindle
• Used to hold work that is too large or of such a
shape that it cannot be held in a chuck or
between centers
• It has slots or threaded holes
• W.piece is clamped using T-nuts in the slots or
threaded holes

LATHE FIXTURES
Collet Chucks:
• that forms a collar around the object to be held and exerts a strong
clamping force on the object when it is tightened.
• A external collet is a sleeve with a (normally) cylindrical inner
surface and a conical outer surface
• Used for very small parts

LATHE FIXTURES
Mandrels:
• Mandrels are internal locators used for machining of the
outside diameter of the workpiece concentric with finished
bores.
• Mandrels are shafts specially made to hold work to be
machined concentrically around a previously bored or drilled
hole
• There are two general types, plain and expanding
• Plain mandrels have a 0.006-in. taper per foot
• There must be a mandrel for each hole size

LATHE FIXTURES
Plain Mandrels:

LATHE FIXTURES
Sleeve-type Expanding Mandrels:
• It is used for high degree of concentricity.
• It provides the adjustment of locating
diameter to suite the variation in the bore
size of the workpiece.

LATHE FIXTURES
Mandrel for Threaded Parts:
• Used for holding previously threaded
workpiece or w.p with internal threads

Everything You Need to Know About Jigs and Fixtures

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