Clamping devices:

• If the work piece cannot be restrained by the locating devices or elements, it become necessary to clamp the work piece in jig or fixture body.
• The most common example of clamping devices is bench vice.
• The purpose of the clamping is to exert a pressure to press a work piece against the locating surfaces and hold it there in a position to the cutting forces.
• In bench vice the movable jaw of the vice exert force on the work piece, there by holding it in correct position of location in the fixed jaw of the vice.
• The commonly used clamping devices are follows:

(A): Clamping Screws:

Clamping screws are used for light clamping. Clamping screws are shown in fig.

(B): Hook Bolt Clamp: This is very simple clamping device and is only suitable for light work and where usual tip of the clamp is inconvenient. The typical hook bolt clamp is shown.

(C): Bridge Clamp:

It is very simple and reliable clamping device. The clamping force is applied by spring loaded nut.

(D): Heel Clamp: These consist of a rusted plate, center stud and heel. This trap should be strengthen at the point where the hole for the stud is cut out, by increasing the thickness around the hole. The design differ from simple bridge clamp in that a heel is provided at the outer end of the clamp to guide its sliding motion for loading and unloading the work piece.

(E): Swinging Strap (Latch Clamp):

This is a special type of clamp which provides a means of intry for loading and unloading the work piece. For this the strap (latch or lid) can be swing out from the work piece. The typical swing strap or latch clamp is shown in figure.

(F): C-Clamp:

To unload the work piece, the locking nut is unscrewed by giving it about one turn and this releases the c- clamp. When the clamp is removed or swing away the work piece can freely pass over the nut. To reverse procedure is adopted for loading the work piece.

Locating Devices

• The pins of various design and made of hardened steel are the most common locating devices used to locate a work piece in a jig or fixture.
• The shank of the pin is press fitted or driven into the body of jig or fixture.
• The locating diameter of the pin is made larger than the shank to prevent it from being forced into the jig or fixture body due to the weight of the work piece or cutting forces.
• Depending upon the mutual relation between the work piece and the pin.
• The pin may be classify as follows:

(A): Locating Pins:

When reamed or finally finished holes are available in work piece, these can be used for locating purpose of the manner as shown, and these are two types of locating pins: - Conical locating pins - Cylindrical locating pins

(B): Support Locating Pins:

• With these pins (also known as rest pins) buttons or pads the work piece with flat surfaces supported at convenient.
• In the fixed support pins the locating face is either ground flat or curved.
• Support pins with flat head are usually employed and provided location and support to machine surface, because more contact area is available during location.
• It would insure accurate and stable location. The spherical head or round head rest buttons are used for supporting rough surfaces (unmachined and cast surfaces) because they provide a point support which may be stable under these circumstances.
• Adjustable type support pins are used for work piece whose dimension can vary.
• For example sand casting, forging or unmachined faces.

(C): Jack Pins:

• Jack pins or spring pins are also used to locate the work piece whose dimension are subjected to variation.
• The pin is allow to come up under spring pressure or conversely is pressed down by the work piece.
• When the location of the work piece is secured the pin is locked in this position by means of locking screw.