Spring Locating Pins Information
A workholder is any device that is used to lock and hold a part against the forces of machining. Workholders are also used at other stages of manufacturing, such as assembly or welding, that require the workpiece to be held in place for repeatability, precision, production efficiency, safety, and other benefits to production and productivity. A basic workholder is a simple clamp. However, holding a workpiece in place can also include complex solutions that are specially designed using both off-the-shelf and custom-manufactured parts.
Locating pins and fixturing pins align or affix workpieces to a workholder with very tight tolerances. When regular part handling mechanisms in machining or assembly applications are not steady or precise enough to place objects in position for a particular process, standard locating and fixturing pins can ensure an accurate alignment. These pins can be activated manually, pneumatically, hydraulically, or electrically. When space in the workholder is tight, special pins, spring locating pins, are often used to apply lateral pressure or side force to the workpiece. Often, the part is positioned in place against fixed pins.
Spring locating pins consist of a barrel, a spring inside of the barrel, and a specially shaped pin assembled into the barrel with a preloaded force on the spring. The spring locating pin is usually press fit into a hole in the workholder for use in fixturing or locating applications. This design allows the pin head to apply a force on the workpiece that is perpendicular to the centerline of the spring locating pin.
The series of images above shows the sequence of a part being placed in the workholder. First, the part is moved toward the fixture. Next, the part is positioned against the locating pins. Finally, with additional pressure to overcome the pin spring force, the part is secured and held in place. Additional clamping may be applied once the part is precisely located.
When specifying spring locating pins, the three main properties to take into consideration are shape/dimensions, material type, and side force. The four dimensional components of a spring locating pin are body diameter, body length, toggle (pin) diameter, and toggle length. Material selection for the spring locating pins themselves is usually plastic, stainless steel, or steel. The body is often constructed of steel, stainless steel, or aluminum. Side force required is the force at right angles to the spring locating pin and can be as light as a pound or up to one hundred or more pounds.
Spring locating pins should be considered an option whenever you need to apply light workpiece holding pressure or to temporarily hold the part in a precise location while heavier clamping pressure is applied. They are especially useful in tight spaces where force cannot be easily applied by other means.