tumble jig

TUMBLE JIG

Presented byBharat.k.manviReg no : 100926022

CONTENTS Introduction Construction of jig Construction elements of jigs Tool bodies Requirement of tool bodies Tool guiding elements Installation of drill bushings Fastening elements Advantage of tumble jig Uses of jig Fundamental difference between fixture with

a jig

INTRODUCTION

A jig is a special device that holds, supports, or is placed on a part to be machined.

It is a production tool made so that it not only locates and holds the work piece but also guides the cutting tool as the operation is performed.

Jigs are usually fitted with hardened steel bushings for guiding drills or other cutting tools.

A jig is any of a large class of tools in wood working, metal working and some other crafts that help to control the location or motion (or both) of a tool.

The primary purpose for a jig is for repeatability and exact duplication of a part for reproduction.

CONSTRUCTION OF JIG

jigs are made up of the construction elements such as tool bodies, tool guides and fastening elements.

Tool body is the rigid base that holds the locating elements, clamping elements and support the work piece, while the production process is performed.

The size, shape, the material and the construction of the tool body is largely governed by the work piece to be machined.

As jig has to incorporate the additional feature of guiding the tool, tool guiding elements in the form of bushings are inserted in the drill jig plate.

The cutting tool is guided through bushing and drills the work piece as required.

The choice of bushing depends on the type of jig.

Fasteners are yet other element used in construction of jig.

CONSTRUCTION ELEMENTS OF JIGS

Tool bodies.

Tool guiding elements.

Installation of drill bushings.

Fastening elements.

TOOL BODIES

It is the main part of the jig which provides a rigid base to mount all the locating, clamping and guiding elements, as well as all auxiliary parts and mechanisms.

REQUIREMENT OF TOOL BODIES

They should take up all the forces developed during machining process.

They should be rugged rigid and yet light in weight for easy transportability.

They should facilitate convenient and rapid loosening and removal of work piece.

They should provide easy cleaning and disposal of chips and cutting fluids.

The bodies should provide for simple alignments for setting up and clamping the fixtures.

They should be simple and comparatively inexpensive to manufacture.

They should incorporate all safety engineering requirements.

TOOL GUIDING ELEMENTS

In a jig, to guide the tool, such as drills, reamers, boring bars etc. various types of tool guiding elements i.e. bushings are used.

There are three types of bushings. 1.Fixed bushings. 2.Renewable type. 3.Special type.

FIXED BUSHINGS

As the name reveals these are one time bushings. Once fixed they can not be removed.

These are called press fit bushings. These are used in limited production

tooling where no bushing change is required.

These being press fit their removal and replacement results in inaccurate work piece.

There are two types, 1) plain bushings (head less bushings) 2) headed bushings (flanged bushings)

RENEWABLE BUSHINGS

In long run productions inside diameter of drill bushing is subjected to severe wear due to continuous contact with cutting tool. This needs periodical replacement with new bushings.

INSTALLATION OF DRILL BUSHINGS

In jig work correct fitting of drill bushing is important. If they are not properly installed they could fall out during use or bind and break the tool.

FOLLOWING POINTS TO BE OBSERVED WHILE INSTALLATION

Holes meant for receiving the drill bushing must be made undersize and perfectly to allow the bushing to fit correctly in case of press fit bushing.

The bushing should be long enough to support and guide the tool properly. Usually

L = d to 2d where L = length of bushing. d = tool diameter. The wall thickness of the bushing should be

able to withstand all the cutting forces and maintain tool accuracy.

For most applications there should be a gap between the bushing and work for chip clearance known as bushing clearance.

This should be (d to 1.5d)

In case of precision and extreme accuracy works the clearance should be less.

FASTENING ELEMENTS

Many types of fasteners are used in developing the jigs. These are screws, bolts, nuts, washers, keys, dowel pins, etc.

ADVANTAGE OF TUMBLE JIG

It contains bushing on two or more sides for the purpose of the drilling on different sides of the part.

After one face is drilled, the next side may bedrilled by simply flopping the jig to expose this side to the drill spindle.

greater accuracy can be obtained and less part handling is necessary.

ADVANTAGE OF EMPLOYING JIG

It eliminates the marking out, measuring, and other setting methods before machining.

It increases the machining accuracy, because the work piece is automatically located and the tool is guided without making any manual adjustment.

It increases the production capacity by enabling a number of work pieces to be machined in the single set up.

It reduces the operator's labour and consequent fatigue as the handling operations are minimised and simplified.

It reduces the overall cost of machining by fully or partly automatising the process.

USES OF JIGS

Jigs and fixtures are used to reduce the cost of production as there use elimination being out work and setting up of tools.

To increase the production. To assure the high accuracy of the

parts. To control quality control expenses. To provide for interchangeability. To enables heavy and complex shaped

parts to be machined by holding rigidly to a machine.

Less skilled labour. Saving labour. There use partially automates the

machine tool. Improve the safety at work, thereby

lowering the rate of accidents.

FUNDAMENTAL DIFFERENCE BETWEEN FIXTURE WITH A JIG

A Fixture holds and position the work but does not guide the cutting tool, whereas a Jig holds, locates and as well as guides the tool.

The Fixtures are generally 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.

The fixtures are employed for holding work in Milling, Grinding, Planning, or Turning operations, whereas the Jigs are used for holding the work and guiding the tool particularly in Drilling, Reaming or Tapping operations.

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