Assembly in Action: Coiled Spring Pins Improve Trigger Assembly
February 20, 2009
Founded in 1917, Norica Laurona (Eibar, Spain) manufactures shotguns, and compressed-air pistols and rifles. Recently, the company found it was having problems manufacturing the trigger assemblies for one of its air rifles because of the pins it was using to hold them together.
Each assembly is composed of a housing, a safety lever, three internal mechanisms and the trigger itself. The parts were being held in place with five separate pins, each of which was secured with a pair of E-rings, one at each end.
Four of the machined pins shared the same 3-millimeter diameter, but were of three different lengths. The fifth pin measured 5 millimeters in diameter. Not surprisingly, keeping four different pin sizes and two different E-ring sizes in stock was often a problem. The process of manually installing the five pins and 10 E-rings was also very time consuming, because operators had to pay close attention to ensure the correct pins all went in the correct holes.
To solve the problem, Norica Laurona switched from the solid, machined pins it had been using to a set of self-retaining light-duty coiled pins from Spirol International Corp. (Danielson, CT). Because the new pins are self-retaining, the switch meant the E-rings could be completely done away with. In addition, because they were no longer being held in place by the clips, the four 3-millimeter pins could be standardized at a single length.
In terms of parts numbers, Norica Laurona reduced the number of part types from six to two and the number of parts from 15 to five.
During installation, a coiled spring pin is compressed so that it will fit easily in the hole, or holes in which it is being installed and then allowed to relax. The pins’ inherent flexibility allows them to absorb wide manufacturing tolerances and makes them self-retaining.
In operation, the fasteners serve as a kind of “mini shock absorber,” in that they help isolate the assemblies in which they are installed from shock loads and vibration. The pins provide a uniform radial force against the surfaces of the holes in which they are installed across 270 degrees of contact.
Because of their flexibility, the coiled pins require far less insertion force than solid machined pins. In the case of the Norica Laurona application, this means trigger assemblies are that much easier to disassemble during maintenance in the field. The pins are supplied with a phosphate and oil finish, which provides corrosion protection and matches the color of the rest of the trigger assembly.
For additional information on pins and other mechanical fasteners, call 860-774-8571 or visit www.spirol.com.