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Design News, February 2013

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Materials & Assembly Specifying Captive Panel Screws By Design Understanding the key drivers that influence the choice of captive panel screws helps engineers select the best ones for their application. by Lillyanna Penn, Pennengineering MISALIGNED AXIS will often be considered for equipping panels, covers, drawers, racks, and other access points. In addition to providing secure attachment and controlled access, these types of fasteners are designed to keep the parts count to a minimum for easy and efficient handling and installation. They also mount permanently to eliminate any risks associated with loose hardware that could fall out, get lost, or be misplaced, potentially causing damage to other components. While all panel fastener assemblies with captive screws deliver these fundamental advantages, dozens of potential choices abound within this hardware category. How should the design engineer proceed on the road to specification? By identifying which mounting style is best suited for the application and determining which features of the fastener will be appropriate for the application. The standard mounting styles of THREADS CAM captive panel screws are self-clinching, flare-mounted, or float/flare-mounted technologies. Self-clinching types install flush, when using the shortest screw length, on the backside of a panel, so there are no protrusions on the side of the sheet opposite installation. These screws require minimal panel preparation. No secondary operations will be necessary, which can help maximize productivity along the line. The fastener is inserted into a properly sized hole in the mounting sheet and, by applying sufficient squeezing force from a press, becomes a permanent part of the assembly. As a result, the sheet material surrounding the hole is forced into the fastener's undercut, securing against axial movement and against rotation by a displacer. For any self-clinching fastener the relationship between fastener and sheet material is critical. Three basic requirements are necessary for a suc- THREADS DRIVE NORMALLY Design News | february 2013 | www.d esign n ews.com –46– Anti-cross threading technology can correct off-angle installations of self-clinching, flaremounted, and floating captive panel screws. Source: PennEngineering A fter a design engineer makes the initial decision to specify fastening hardware for an attachment application, the process turns to narrowing the field of candidates by evaluating application requirements, identifying the most appropriate fastener solution, and then choosing the best fastener for the job. During the decision-making process, engineers consider a fastener's mounting style, features and functions, and costs, among other critical drivers that ultimately govern proper selection. An understanding of such key drivers, and how a particular fastener does or does not conform to them, can make all the difference in achieving application success. One example offers universal lessons for the selection of other hardware. This is a well-populated family of panel fastener assemblies that integrate captive screws. These assemblies

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