From: "Gabriel L Romeu" <romeug_at_erols.com> > Just out of curiosity Mike, would a flanged, tight fitting mechanical > fastener (nut, bolt, and washers/ or rivet) transfer the stress as if it > weren't drilled? In general, no. Or at least I wouldn't take it into consideration without considerable analysis to justify. Tension across the hole would not transfer, shear would be iffy and only pure compression would be likely. But in the latter, other factors, such as the way the hole is made (cut, drilled, punched), the stresses induced by making the hole and even thermally induced changes in the properties around the hole are a factor. Even the difference in the alloy used in the base metal and the bolt would come into effect. Tight fitting would have to be just that - and that's too tricky to guarantee. It's too complicated to consider most of the time. If in doubt, get a heavier crossbar before drilling. > > My conjecture is that these general rules would be far different for a > solid material as opposed to tubing as tubing relies on continuous > surface runs for strength. Is this true? The only significant difference that comes to mind is that thin-walled tubing has buckling near the hole to consider. Other than that, there isn't much difference. BTW, I hope no one read my previous post to imply _no_ reduction in strength. Any hole will reduce the strength. However, small holes in the right place minimize the strength reduction and the sizes I suggested for kayak loads probably won't reduce the strength in a significant way. If you stack four or more kayaks on a l-o-n-g crossbar, YMMV; I'm thinking two on a car-width bar. Make sure you do a clean job on the hole. If you want to make a lot of changes to a crossbar, consider using the crossbar as a support to hold a 2x4 or 2x6 on the roof and do all the fiddling to that. If you shape the bottom of the wood (thin side down) to fit the roof and pad it with carpeting or solid foam, little stress is put into the vehicle roof. The wood can take a lot - a 1/4" hole in a nominal 4" deep piece of wood is nothing compared to a 1/4 hole in a steel crossbar that's 1" deep or less. Mike *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************Received on Sat Dec 15 2001 - 13:35:00 PST
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