Page 42 - CITS - Fitter - Trade Theory

FITTER - CITS

Scroll chucks are chucks in which each jaw moves simultaneously by turning the open/close screw on the side
of the chuck. Since the jaws move simultaneously, the center point of the workpiece and the center of the chuck
always coincide.
The main advantage of this chuck is that it can be easily handled even by beginners. Most scroll chucks are of
the 3-jaw type.
In the case of independent-jaw chucks, each jaw moves independently. For this type of chuck, 4-jawed chucks are
the most common. Since each jaw moves individually, a certain level of skill is required to operate the independent-
jaw chuck. However, it has the advantage of being able to grasp a variety of workpiece shapes.
c Power chuck
Power chucks are chucks that use hydraulic or pneumatic pressure to automatically open and close the jaws
to grip the workpiece, and are widely used in processing sites. There are automatic bar feeders that enable
continuous processing of bars, and oscillating chucks that can firmly hold even rough-surfaced workpieces.

d Collet chuck
Collet chucks are a type of chuck that uses a collet, a cylindrical part with multiple slits, to hold a workpiece. Since
the collet holds the workpiece as if wrapping it, the force is dispersed and the workpiece will not be damaged.
Collet chucks are used in lathes to hold workpieces and in machining centers (MC) to hold tools.
e Other chucks
There are special chucks designed for specific workpiece shapes or indexing chucks that can index to 90
degrees, 120 degrees, etc. while gripping the workpiece. Indexing means moving the rotary axis to the target
angle precisely.

Chucks that are compatible with automation include the automatic jaw changer (AJC) system, which can
automatically change jaws, and the automatic chuck changer (ACC) system, which can automatically change the
chuck itself.
• Lathe center
When machining a relatively long workpiece with a small diameter, the workpiece will not be chucked, but
supported by a device called a lathe center on both sides of the workpiece. The lathe center is attached to both
the headstock and the tailstock. Since the lathe center supports the end faces of the workpiece, the workpiece
can be machined to the very edge of both ends.
Since the rotation of the main spindle is not transmitted to the workpiece by just attaching both ends to the lathe
center, a driving plate or work carry is used to transmit the rotation of the main spindle to the workpiece. This
method can hold thin or rectangular-shaped workpieces that cannot be gripped by the chuck.
• Holding devices for grinding machine
1 For cylindrical shaped workpiece for cylindrical grinding machines, which grind the periphery and end faces
of cylindrical workpieces, the method of gripping the workpiece is similar to lathes. Thus, like lathes, they
mainly use chucks and centers.
However, centerless grinding machines, which are more powerful for mass-production machining, do not
use jigs or other fixtures. In centerless grinders, the workpiece is supported and machined at three points:
the grindstone, the supporting plate, and the regulating wheel.

27

CITS : CG & M - Fitter - Lesson 4 CITS : CG & M - Fitter - Lesson 4