Grippers are special forms of supports and rests. The most common ones are round with a diamond serrated face but a wide choice of face materials and configurations are available, as shown in Figure 7-39. Grippers are hard, replaceable inserts used to provide additional holding force and/or wear resistance when installed in a fixture. These grippers are designed to slightly penetrate the workpiece to significantly increase gripping force, rather than relying on static friction alone. There are many different styles of grippers: Round, Round Counterbored, Square, Square Counterbored, Edge Grippers, Gripper Contact Bolts, Gripper Swivel Contact Bolts, Gripper Swivel Pads, and Gripper Contact Pads, shown in Figure 7-40. Standard grippers are made
from M-2 tool steel, heat treated Rc 60-62, black oxide finish.
Figure 7-39. Grippers are available with a wide variety of contact faces
Figure 7-40. Grippers come in a wide variety of styles and for many applications.
Counterbored Grippers are useful whenever fastening from behind or the side is not possible. Fasten with a standard Socket-Head Cap Screw. Round Grippers can be recess-mounted in a flat-bottom hole, or surface mounted to use as a rest pad. When grippers are installed in a hole, they should project 50 to 100% of serration height for maximum effectiveness (serration height is .047" on grippers with .094" x 90° serrations, .062" on grippers with .125" x 90° serrations). Round Grippers are also available with a carbide insert. The Carbide-Tipped Grippers are economical and impact resistant while providing extra durability. They are made from Alloy steel, are heat treated, with brazed carbide insert, and are black oxide finished. These come in either rear mount or counterbored. Round Grippers are also available in solid carbide.
Another variety of Round Gripper is the Diamond-Faced Grippers, which have an abrasive-diamond surface permanently fused to a hardened stainless steel pad. This abrasive surface, comparable to a 100-grit abrasive, provides significant holding force with relatively low clamping pressure and minimal surface marring. The diamond-particle surface also offers excellent wear resistance. The gripper body is made of hardened stainless steel for high strength and excellent corrosion resistance. These grippers are made of 17-4 stainless steel, heat treated Rc 43-46, with a permanently fused abrasive-diamond surface.
A non-abrasive variety of gripper has a urethane surface permanently bonded to a stainless steel pad. This non-marking, non-staining urethane provides excellent protection against damage to finished workpieces. The bubbled texture of the urethane surface offers firm gripping, yet allows air to escape so that no suction is created under load. Urethane also provides excellent wear resistance, and is available in three firmnesses to suit a wide variety of applications.
Flat-Faced Grippers are available with a carbide insert, hardened steel, hardened stainless, or made from Delrin®. The Flat-Faced Carbide Grippers provide extra abrasion and wear resistance, but are otherwise similar to the flat round steel grippers. Flat-Faced Steel Grippers are made from 8620 steel. They are carburized-hardened and have a black oxide finish. The stainless steel pad is made from 17-4 stainless steel, and is heat treated to Rc 43-46. These stainless grippers provide high strength and excellent corrosion resistance. Flat Delrin® grippers are useful to avoid marring a finished part surface. They are made from White Delrin® 500.
Square Grippers have the same serrated faces as the round style. They are available for back mounting, or counterbored for face mounting, and available in steel, steel with a carbide insert, or made from solid carbide. Gripper Contact Bolts are fully threaded contact bolts with a carbide-tipped gripper head. They can be used as an adjustable support, or as a contact bolt in a clamp. Gripper Swivel Contact Bolts are threaded contact bolts with a built-in swivel ball to hold a Round Gripper. This swivel ball, held by a retaining ring, is removable to allow installing any of the six different gripper types. A fastening screw is furnished with the contact bolt. This screw serves as a positive stop to prevent the ball from swiveling too far. A Gripper Swivel Contact Bolt can be used as a contact bolt, or as a support. The mini version of the contact bolt, with thread sizes up to 5/16 or M8, is a threaded contact bolt with a built-in swivel ball held by a retaining ring. You may choose from the three gripper types, serrated, flat steel or Delrin®. The gripper face is machined directly on the swivel ball. A positive stop prevents the ball from swiveling too far.
The Gripper Swivel Pad is a rest pad with a built-in swivel ball to hold a Round Gripper. This swivel ball, held by a retaining ring, is removable to allow installing any of the six different gripper types. A fastening screw is furnished with the swivel pad. This screw serves as a positive stop to prevent the ball from swiveling too far. Gripper Swivel Pads can be surface mounted or installed in a counterbored hole. Since the gripper is attached to the swivel ball, any style of Round Gripper can be attached to the swivel pad. The mini style of these swivel pads does not have a removable gripper pad, but comes in three styles -- serrated and flat steel and Delrin®. Gripper Swivel Screws are screw clamps with a hardened tool steel swivel ball, either serrated or flat. A positive stop prevents the ball from swiveling too far.