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.

INTRODUCTIONThey 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 operationsWork 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.

TEMPLATE JIGS

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.

PLATE JIG

PLATE JIG

TABLE JIG

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.

SANDWICH JIG

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.

MODIFIED ANGLE-PLATE JIG

MODIFIED ANGLE-PLATE JIG

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.

BOX JIG

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.

CHANNEL JIGS

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

LEAF JIGS

LEAF JIGS

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

INDEXING JIGS

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..

PUMP JIG

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

GENERAL CONSIDERATIONS IN THE DESIGN OF DRILL JIGS

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.

GENERAL CONSIDERATIONS IN THE DESIGN OF DRILL JIGS

GENERAL CONSIDERATIONS IN THE DESIGN OF DRILL JIGS

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

Chip Control:

GENERAL CONSIDERATIONS IN THE DESIGN OF DRILL JIGS

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.

Types of Standard Jig Feet:

GENERAL CONSIDERATIONS IN THE DESIGN OF DRILL JIGS

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 fixturesFollowing 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

MILLING MACHINE VISES

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

SPECIAL VISE JAWS

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 FIXTURESHYDRAULIC CLAMPING FIXTURE:

MILLING FIXTURESSPRING TYPE FIXTURE:

MILLING FIXTURESCLAMP 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

VACUUM FIXTURE

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.

INTERNAL BROACHING FIXTURES

INTERNAL BROACHING FIXTURES

EXTERNAL BROACHING FIXTURES

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

GRINDING FIXTURES (use of magnetic chuck parallels)

GRINDING FIXTURES (use of magnetic-chuck V block)

GRINDING FIXTURES

LATHE FIXTURESThree-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

THREE-JAW UNIVERSAL CHUCK

LATHE FIXTURESFour-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

FOUR-JAW AND SIX-JAW CHUCKS

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

MAGNETIC CHUCKS

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

FACEPLATE AND T-NUTS

FACEPLATES

FACEPLATES

LATHE FIXTURESCollet 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 FIXTURESCollet Chucks:

LATHE FIXTURESMandrels:

• 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 FIXTURESPlain Mandrels:

LATHE FIXTURESSleeve-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 FIXTURESMandrel for Threaded Parts:• Used for holding previously threaded

workpiece or w.p with internal threads