JIGS AND JIG BUSHES

A drill jig is a device for ensuring that a hole to be

drilled, tapped or reamed in a workpiece will be

machined in the proper place.

The position of each hole on the workpiece need not

be located with the aid of a square, straight edge,

scriber and centre punch.scriber and centre punch.

In addition to locating and clamping elements, jig

has bushings to guide the tool (drill).

Locating and clamping elements in drill jigs are

subjected to high torque along the axis (force in the

direction perpendicular to the axis) of the cutting

tool.

Requirements of a good drill jig:

1. Quick and accurate location of the workpiece.

2. Easy loading and unloading of the workpiece and

prevention of wrong loading.

3. Prevention of bending or movement of the

workpiece during drilling.

4. Ample chip clearance with facilities for swarf4. Ample chip clearance with facilities for swarf

removal and cleaning.

5. Light weight to minimize operator fatigue due to

repeated handling.

6. Prevention of loss of loose parts by chaining

them to the jig body.

7. Clearance for overshoot of the drill.2

DRILL BUSHES

Bushes are made up of water hardened carbon steel

with 0.85 to 1% carbon and 0.5 to 0.9% manganese.

The material is hardened to HRC60-64 to minimize wear

due to contact with hard rotating tools.

Inside and outside bore are ground within 0.001mm

concentricity.concentricity.

Inside diameter is ground precision running fit (F7) with

the drill/reamer.

Outside diameter is made press fit (p6), precision

location fit (h6) or precision running fit (f6), depending

upon the function and application of the bush.3

These are the most common type of bushes.

Pressed (interference fit) in the bush plate (jig plate).

Two types: Headed bush, headless bush

Headed bushes are preferred to headless because

headless bush may slide axially into the bush plate

PRESS FIT BUSHES

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�Used for continuous or large batch production.

�After wear and tear these bushes are replaced.

�Replacement is simplified by making the outsidediameter precision location fit (h6).

�The use of liner in the jig plate provides hardenedwear resistant mating surface to the renewable bush.

RENEWABLE BUSHES

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�When a hole in the workpiece

requires two operations such

as drilling and reaming, slip

bushes are used.

�In mass production the

changeover of these bushes

should be effected quickly.

SLIP BUSHES

should be effected quickly.

�The bush is provided with a

flat on the head similar to the

renewable bush and a circular

cutout in the flange to

facilitate quick assembly and

removal.

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These bushes are part of the clamping system.

Along with the threaded bush a liner bush is used foraccurate location.

Collar of the liner bush is placed in the opposite side totake the axial thrust of the screw.

The liner bush is prevented from rotation by a grubscrew.

THREADED BUSHES

screw.

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Some workpieces/ operations require unusual type

of bushes.

Ex: Drill bush for curved surface, drill bush for

inclined surface, plate bush (when centre distance

between two holes is less)

These are modified forms of standard bushes.

SPECIAL BUSHES

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Depending upon their construction and method of

operation, drill jigs can be classified as follows:

1. Plate jigs and channel jigs with workpiece pots

2. Angle plate jigs

3. Turn-over jigs

4. Leaf or latch jigs

VARIOUS TYPES OF JIGS

4. Leaf or latch jigs

5. Box jigs

6. Trunnion-type indexing jigs

7. Sandwich and pump jigs

8. Jigs for multi-spindle machines

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PLATE JIG AND CHANNEL JIG

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1. Plate-type jigs mainly consist of a single bush

plate with a provision for location and the

clamping of workpiece.

2. The workpiece profile is located by six location

pins and clamped by two knurled screws

against the location pins.

PLATE JIG AND CHANNEL JIG

3. Sometimes, the jig is made channel shaped.

4. There should be enough clearance below the

workpiece for overshoot of the drill after

passing through the workpiece. This can be

achieved by providing a resting pot for the

workpiece.11

LEAF OR LATCH JIG

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LEAF OR LATCH JIG

1. These have a hinged jig (bush) plate.

2. The jig plate can be swung aside to provide

clear path for loading and unloading the

workpiece from the top.

3. The jig plate must have a positive resting face

to ensure that the axes of bushes are verticalto ensure that the axes of bushes are vertical

during drilling.

4. The jig plate is clamped against the resting

face by an eyebolt.

5. The open slot in the jig plate quick clamping

and unclamping of the jig plate.13

BOX JIG

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1. Workpieces having holes on a number of sides

can be drilled economically with box jigs.

2. One side is open for loading and unloading of

the job.

3. The open side is provided with a hinged latch

which often houses bushes and clamping

BOX JIG

which often houses bushes and clamping

screws.

4. The jig is fitted with bushes on various sides

and suitable jig feet on the opposite sides.

5. It reduces number of setting steps, thereby

increasing the accuracy of location.15

TUMBLE JIG

� When a box jig

contains bushings on

two or more sides for

the purpose of

drilling, it is known as

a tumble jig.

� It has sets of jig feet

on opposite sides of

the workpiece faces.

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TRUNNION JIG

1. Used for drilling from a number of sides on large and

heavy workpieces.

2. It is similar to box jig.

3. For easy tumbling, the jig body is provided with

pivots at both ends.

4. The pivots are supported with ball bearings in

supporting brackets at both ends.supporting brackets at both ends.

5. The heavy jig and the trunnion remain stationary

during drilling.

6. The drill machine spindle must be moved to align

with the drill bushes in the jig.

7. Consequently, trunnion type jigs can be used on only

moveable spindle machines such as radial drilling

machine. 18

LEAF TYPE DIAMETER JIG

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SANDWICH JIG

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SANDWICH JIG

1. These are plate jigs with guide pillars for

alignment of jig plate with the base plate.

2. The workpiece is located on the base plate by

pins. The base is aligned with the jig plate by

guide pillars.

3. In sandwich jig, the workpiece is clamped like a

sandwich between the base plate and the jigsandwich between the base plate and the jig

plate.

4. The jig plate can be removed to load and unload

the workpiece.

5. Theses jigs are best suited to workpieces having

two parallel machined surface square to the axis

of drilling.21

PUMP JIG

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PUMP JIG

1. These are smaller versions of sandwich jig.

2. Instead of removing the jig plate completely

from guide pillars, it is merely raised above to

provide passage for loading and unloading of

the workpiece.

3. The guide pillars attached to the jig plate have

rack gear teeth on one side.

4. The pinion gear meshing with the rack can be

rotated by a handle to raise or lower the rack

pillars and jig plate attached to them.

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Thank You

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27Fig. 2. Hardness of cutting tool materials as a function of

temperature