In selecting the proper fastener one must look at all values that the fastener will be subject to: shear, tensile, torsion...there are cases made for either threaded fastener or rivet and even a newer approach: the rivnut which is essentially a rivet with a threaded insert to allow the use of machine screws. One must carefully calculate the loads that the fastener will be subjected to, allowing for a margin of safety and error. When those parameters have been discovered then it is time to determine the appropriate fastener.
When the fastener is selected, the installation of that fastener becomes paramount. The best rivet is useless if the installation was not performed correctly, which also holds true to an improperly tapped machine screw.
I have seen many cases of booms and masts where the owners hated the rivets, drilled them out, replaced them with machine screws, only to call me in to ask why their outhaul was pulled out of the boom, or the tang on the boom for the vang ripped the screws straight out. Or, the best yet, the owner drilled out his gooseneck on his Selden Spar...replaced them by tapping in 1/4-20 MS...first jybe and the gooseneck parted from the mast, the threads pulled smooth.
Use caution, and practice solid engineering principals.
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01-23-2008, 08:01 AM
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