profdant139 wrote:
Chum lee, by drilling and tapping, you do not mean self tapping, right? Do you mean using a tap and die set to accommodate a threaded bolt or machine screw?
Just trying to make sure I am on the same page with you.
It really depends on the thickness of the steel structure you are attaching to. In your initial post you say "pretty beefy -- either I beams or box beams." As an engineer myself, that means nothing to me. Something more like "the flange is .250" thick mild steel" tells me what I need to know.
If your structure is much more than about .125" (1/8") thick, IMO you are getting to the reliable limit of the best self drilling/tapping machine screws and you would be best to pre-drill a pilot hole of the appropriate truncation diameter for the treads you choose to use. You could try (test) using the fasteners you select to see how well they perform (penetrate) in your intended application. As others have pointed out there are literally thousands of different types of threaded fasteners, some/many which may not be available to you at your current location. Remember, you may need to remove/reuse these fasteners at some future date. If they fail upon intallation/removal for what ever reason (corrosion, time, over torque, etc.) where does that leave you? Think about that, . . . . . now.
IMO, the correct way to do what you are doing is to use a captive nut and an SAE or ISO grade fastener, but because your trailer is already built, and this is an addition, so that may not be practical.
IMO, hand tapping the treads and using the appropriate (automotive grade or SAE) fastener gives you the best chance of holding your belly pan in place, then being able to remove/reinstall it should the need arise. Good luck whatever you decide.
Chum lee
