JIG AND FIXTURE TOOL - USE AND CONSTRUCTION KNOWLEDGE - FITTER ONLINE NOTE

 Jigs 

1- In metal working a jig is a type of tool used to control the location and motion of another tool.

2- A jigs primary purpose is to provide repeatability , accuracy and interchangeability in manufacturing products . 

3- A jig is often confused with a fixture holds the work in a fixed location 

4- A device that does both functions ( holding the work and guiding a tool ) is called a jig . 

5- Jigs or templates have been known long before the industrial age . 

6- There are many types of jigs and each one is custom - tailored to do a specific job . 

7- Many jigs are created because there is a necessity to do so by the tradesmen . 

8-  To increase productivity , to do repetitious activities and to do a job more precisely .

9- Faster rate of production . Easy to perform the operations even by unskilled workers . 

10-  Layout and marking on individual parts eliminated .

DRILL JIGS

1- A drill jig is a type of jig that expedites repetitive hole center location on multiple interchangeable parts.

2- It is done by acting as a template to guide the twist drill or other boring device into the precise location of each intended hole center .

3- In metal working practice, typically a hardened drill bushing lines have each hole on the jig plate to keep the tool from damaging the jig.

 Types of drill jigs 

 1- Plate and channel jigs, 

2-  Solid jig, 

3- Post jig, 

4- Table jig, 

5-  Box jig, 

6- Sandwich jig. 

7-  Trunnion jig.

 1- Plate and channel jigs- 

1- Jig consists of a drill plate which rests on the component to be drilled. 

 

2- For correct positioning and locating, pins and clips are provided. 

3- For heavier piece parts, sometimes clamps are not used. 

4- Generally a base plate will not be available for this type of jigs.

2- Solid jig 

1- This can be used while drilling small piece parts. 

 

2- The body of this type of jig is machined from a solid block of steel. 

3- Post Jig

1- This is used for location from a bore. 

 

2- The post should be as short as possible to facilitate loading at the same time, it must be long enough to support the work piece.

4- Table Jig

1- It is used, when it necessary to locate the piece part from its face. 

 

2- Accurate seating of the jig on the machine table, four legs will be provided on this type of jig.

5- Box Jig

1- This is made in the form of a box or frame work.

 

2- The component is located and clamped at one position but drilling can be done from different directions as required. 

3- When a box jig contains bushings on two or more sides for drilling from different directions, it is called a tumbler jig. 

4- This jig is meant for small components only. 

6- Sandwich jig 

1- It is ideal for thin or soft work piece which may bend or warp due to force while machining.

 

In this type of jigs, component will be sandwiched between the base plate and the drill plate. 

7- Trunnion jig 

1- This can be used when large or awkwardly shaped workpieces are to be drilled from different directions.

 

2- This is a further modification of the box jig which is carried on trunnions and rotated from station to station and positioned, using an indexing device. 

Constructional features of drill jig 

The basic features of a drill jig are

1-  Base plate or jig body .

2- Drill plate or jig plate .

3- Drill bushes locating pins .

4- Clamps.

1- Base plate

 1- This provides a rigid support for mounting piece parts, locating pins etc. 

2- In some drill jigs like plate and clamp jigs there will be no base plate.

2-  Drill plate 

1- It holds the drill bushes. Cutting tools are guided by means of the drill bushes. 

2- Un bushed holes made on the drill plate are sometimes used for small runs. 

3- Drill Bushes

1- They are used to locate and guide drills, reamers, taps and any other revolving Drill bushes tools commonly used to make or modify holes.

Types of drill bushes 

1- Press fit bushes.

2- Renewable bushes.

3- Liner bushes.

4- Press fit bushes are made in two forms.

5- Head.

6- Headless.

7- These bushes are used where frequent change of bushes is not anticipated.

Renewable bushes are divided into two groups 

1- Slip renewable bushes (slip bushes) 

2-  Fixed renewable bushes 

Slip renewable bushes (slip bushes) 

1- These bushes are used when more than one operation is performed in the same location. 

2- Eg : drilling and reaming.

3-  These bushes are used with press-fitted liner bushes and a lock clamp.

 

Fixed renewable bushes 

1- These bushes are used where only one operation is to be performed with each bush, whereas several bushes may be used during the life of the jig. 

2- These are also held in a liner and retained by a screw. 

3- Liner bushes are used to provide a hardened hole where renewable bushes are located. Liner bushes are press fitted to the jig plate.

 

Locating pins or locaters are used 

1- To restrict the movement of the component.

2- To position the piece part with respect to the tool .

3- To facilitate easy loading and unloading of component piece parts.

4- To assist the operator for correct loading (fool proofing).

5- Different types of locating pins are used according to the shape of the component and also according to the hole locators.

6- A few types of locating pins.

 

Clamps 

1- Clamps in jigs are meant for holding the component in position against the cutting force.

2- They also help in rapid loading and unloading of the components.

3- Clamps are fitted in such a way that they do not interfere with the cutting operation.

4- The commonly used types of clamps are: 

1- Strap clamp.

 

2- Cam clamp.

 

3-  Screw clamp.

 

4- Wedge clamp.

FIXTURE

1- A fixture is a work-holding or support device used in the manufacturing industry. 

2- Main purpose of a fixture is to locate and in some cases hold a work piece during either a machining operation or some other industrial process. 

3- A jig differs from a fixture in. that it guides the tool to its correct position in addition to locating and supporting the work piece. 

4- The common type of fixture used for machining operations are.,

1- Milling Fixture.

2- Drilling Fixture.

3- Grinding Fixture.

1- Milling Fixture

2- Turning Fixture.

3- Base Plate 

1- The base plate for a milling fixture is provided with tenons at its bottom for proper location of the fixture with the machine table through tee slots.

2- Two or four hold-down slots are provided in the base plate for rigid clamping of the fixture with the machine table

4- Settings Blocks 

It is used to position the fixture and work relative to the cutter before machining.

5- Balancing Weight

1- It used dynamically balancing the irregular work piece fixed to the turning grinding fixture. 

2- In turning fixture the base plate of the fixture is clamped to the face plate.

6- Vice Plate

Machine vices attached with jaws,that provided an easy method of hold the parts for machining purpose.

Constructional features of a fixture 

1- Common types of fixtures used for the machining operations are 

1- Milling fixture .

2- Turning fixture.

3- Grinding fixture etc. 

2- These fixtures consist of a base plate, standard clamps and locators, setting blocks and balancing weights. 

1- Milling fixture.

2- Turning Fixture.

3- Grinding Fixture.

Base Plate

1- The base plate for a milling fixture is provided with tenons at its bottom for proper location of the fixture with the machine table through Tee slots. 

2- Two or four hold-down slots are provided in the base plate for rigid clamping of the fixture with the machine table. 

3- Standard clamps and locators.

4- These are provided for clamping and locating the work pieces with the fixture as in the case of drill jigs. 

5- The clamps used in the fixtures are very rigid and sturdy.

The Setting Blocks

1- These are used to position the fixture and work relative to the cutter before machining.

2- A feeler is introduced between the cutter and the setting faces of the block for correct positioning of the cutter with the fixture.

Balancing Weight

1- This is used dynamically balancing the irregular workpiece fixed to the turning or cylindrical grinding fixture. 

2- In the case of a turning fixture, normally the base plate of the fixture is clamped to the face plate.

Vice Fixture

1- Standard machine vices, attached with special jaws, provide an easy method of holding parts for machining. 

2- Other types of tooling used for positioning parts relative to each other for fabricating purposes are also commonly referred to as fixtures. 

3- Bending fixtures, assembly fixtures and welding fixtures are examples of this type. 

4- The construction of a fixture depends upon the machining and fabricating methods employed.

Difference between jigs and fixtures 

Jigs

1- jig holds and positions the work piece, guides the cutting tool.

2- Jig is not fixed to the machine table .

3- Jigs are used in drilling machine for drilling, tapping.counter boring, and countersinking etc.

Fixtures 

1- Fixture only hold and position the work piece, does not guide the cutting tool. 

2- Fixture is usually fixed to the machine table.

3- Fixtures are used in grinding, milling, turning, bending and assembling.

Use of fixtures 

1- A great deal of importance is placed today on improving productivity in manufacturing processes. 

2- Application of jigs and fixtures has contributed a lot towards this direction. 

3- Jigs and fixtures are devices used in manufacturing or assembling. 

4- They also facilitate in carrying out special operations accurately.

5- Fixture is a production tool that locates and holds the work-piece.

6- It does not guide the cutting tools, but the tools can be positioned before cutting with the help of setting blocks and feeler gauges etc.

7- Fixtures of different types are made for 

1- Milling.

2- Turning.

3- Grinding.

4- Welding.

5- Assembly.

7- Bending etc.