Page 41 - CITS - Fitter - Trade Theory

FITTER - CITS

Work holding device for different jobs

Definition

Work holding device is a general term for devices that attach and fix a work piece to a machine tool. If the
workpiece is not attached correctly, the machine will not be able to make the work piece precisely. This is why
work holding devices are essential peripheral devices.
Among work holding devices, jigs are the most well-known tool. Jigs are aids for attaching and fixing the workpiece
to the machine tool and for correctly applying the cutting tool to the desired cutting point. There are various types
of jigs.
Principle: The process of locating (or positioning) and securing a work piece for machining process.
 Holding devices for lathe

a Chuck
Generally, chucks are used to attach a work piece to a lathe. Chucks are one of the types of jigs. A chuck is
attached to the main spindle of a lathe and plays the role of transmitting the rotation of the spindle to the work
piece and of holding the work piece tightly so that the work piece, which is rotating at a high speed, does not fly
away due to centrifugal force.

Chucks are widely used to hold cylindrical work pieces that are relatively short in length. When a long, narrow
work piece is set in the chuck, the center of the end face that is not gripped by the chuck must be supported by a
device called a lathe center to prevent deflection (explained later).

Chucks commonly use jaws to hold the work piece. There are a wide variety of chucks, distinguished by the
number of jaws, structure, and drive system.
First, chucks are classified as 2-jaw, 3-jaw, and 4-jaw chucks according to the number of jaws. Generally, 3- jaw
chucks are most commonly used. 2-jaw chucks have two jaws facing each other and are suitable for holding
irregularly shaped work pieces, but the gripping force is not high. Four-jaw chucks can support a work piece at
four points, so they are suitable for holding a plate or block-shaped work pieces.
The architecture of the chuck can be divided into two types: the solid type and the hollow type, which has a
through-hole in the center of the chuck and is hollow. The solid type is more rigid and suitable for heavy cutting,
while the hollow type is lighter and suitable for high-speed rotation.
In terms of jaw drive systems, there are two main types: hand chucks and power chucks. There are also collect
chucks that do not use jaws, instead using a part called a collect to grip cylindrical work pieces.
b Manual chuck
Manual chucks are chucks in which the jaws are opened and closed manually by using a special tool. There are
two types of manual chucks: scroll chucks and independent-jaw chucks.
Manual chucks are chucks in which the jaws are opened and closed manually by using a special tool. There are
two types of manual chucks: scroll chucks and independent-jaw chucks.

26

CITS : CG & M - Fitter - Lesson 4