In addition to fixed and adjustable locators, spring-loaded devices are also used with many jigs and fixtures. Spring-loaded devices include spring locating pins, spring stop buttons, ball plungers, and spring plungers. They play an important role in the operation of many workholders.
Spring Locating Pins
No matter how well a locating system is designed, unless the parts are properly positioned against the locators every time, mistakes result. One device that reduces locating errors is the spring locating pin, Figure 7-41.
The spring locating pins push the part against the fixed locators. This ensures proper contact during the clamping operation. Although not actually locating devices, the spring locating pins do help reduce errors by correctly positioning the part against the locators. In addition, the pins also eliminate the need for a “third hand” when clamping some parts. Their small size and compact design make them very useful for smaller parts or confined space. A protective rubber seal around the contact pin helps seal out chips and coolant.
Figure 7-41. Spring locating pins push the workpiece against the fixed locators to ensure proper contact when the workpiece is clamped.
Figure 7-42. Spring locating pins can be mounted directly in a hole or in an eccentric liner.
Figure 7-43. The eccentric liner allows spring-locating-pin adjustment for parts with greater size variations.
Figure 7-44 shows parts positioned with spring locating pins. These devices can also be used as grippers, or light clamps.
Figure 7-44. Spring locating pins are useful in many workholding applications.
Spring Stop Buttons
The spring stop button, Figure 7-45, is another commonly used spring-loaded device. These units work much like the spring pins, but they are designed for larger parts or where more force is need. Spring stop buttons are made with three different contact faces. The first is a spherical button contact; the other two have a flat contact. The flat-face contacts are made either with or without a tang, Figure 7-46.
Figure 7-45. Spring stop buttons are another form of spring-loaded device. They are used to hold larger parts or when more force is needed.
Figure 7-46. Spring stop buttons are available with a spherical contact button, flat face, or flat face with tag (for thin sheets).
Ball Plungers
Ball plungers are spring-loaded devices. They are used for a variety of workholding applications. As shown in Figure 7-47, the ball plunger contains a hardened ball as a plunger. In many applications, the ball plunger is combined with a ball detent. The ball detent acts as a hardened locating and referencing device for the ball plunger. The ball plunger has a nylon-type locating element on the threads to prevent backing out after installation.
Figure 7-47. A ball plunger and matching ball detent.
Ball plungers often locate workholder elements. As shown in Figure 4-48, one application of the units is for locating an indexing arrangement. Here the part is mounted on a pin and held in place with a knurled knob. The first hole is drilled; then the part is rotated until the ball plunger engages the second ball detent. Finally, the mandrel is locked and the second hole is drilled.
Figure 7-48. Ball plungers and ball detents are often used for indexing operations.
Spring Plungers
Spring plungers are similar to ball plungers, except with a longer stroke. Instead of a ball, the spring plunger has a cylindrical plunger with a rounded end. Spring plungers are well suited for a variety of applications, such as the workpiece ejector shown in Figure 7-49.
Spring plungers are available in various lengths and end pressures, in stainless and mild steel. They are also available with Delrin® plungers for applications where marring is a concern. Like the ball plungers, spring plungers have nylon-type locking element on the threads.
Figure 7-49. Spring plungers have a cylindrical plunger with a rounded end. They are sometimes uses as part ejectors.
Hand-Retractable Plungers
Hand-retractable plungers, Figure 7-50, are another style of spring plunger. Their purpose is to accurately align workholder elements. Like ball plungers, the hand-retractable plungers often provide indexing, but they engage an indexing hole rather than a ball detent. Such alignment both ensures the correct position and provides a positive lock. As shown in Figure 7-51, these plungers are hand operated and must be pulled back to disengage the indexing hole. When the handle is released, a spring advances the plunger into the hole.
Figure 7-50. Hand-retractable plungers are spring-loaded plungers used to accurately align workholder elements in an indexing or referencing hole.
Figure 7-51. Hand-retractable plungers are advanced with a spring action and retracted manually.
Index Plungers and Bushings
Index plungers are precision, heavy-duty assemblies with a retractable spring-loaded plunger and a matching locating bushing. Tapered Index Plungers feature a 15° taper on the plunger tip with a mating taper in the bushing. The taper makes alignment easier and also eliminates any binding during retraction. The rotary-cam version completely retracts when the handle is rotated 180°. Cam surfaces are hardened steel. The standard mount configuration shown in Figure 7-52 has a precision ground body with a whistle notch for orientation with a setscrew (also available with a slightly oversize unground body to allow custom grinding to size).
Figure 7-52. Standard mount style, with whistle notch for alignment.
The flange-mount configuration shown in Figure 7-53 has a precision ground body with a flange used for orientation by fastening with two Socket-Head Cap Screws (also available with a slightly oversize unground body to allow custom grinding to size). Flange mounting is designed for installations where a cross hole for a set screw is not practical.
Figure 7-53. Flange-mount version of index plunger.
The version shown in Figure 7-54 has a blank machinable end for easy adaptation to various actuating devices, including automated setups. Precision ground body (also available with a slightly oversize unground body to allow custom grinding to size).
Figure 7-54. Straight index plunger with blank machinable end.