Originally Posted by Skee75
Msmoto, after the pilot hole is through the interior ceiling, could I use the hole to drill my 2 1/4" from inside the trailer and then keep going through the exterior metal as well?
I suspect one could do this, but why? I have found drilling up creates issues of the waste potentially falling into eyes, and aluminum dust is a disaster if one gets into an eye, cannot be removed with a magnet as steel filings are.
When measured about three times, checked by a second person, drilling from the top is preferred, IMO. The key is to do this very slowly, using a sharp high quality hole saw designed for drilling thin sheet metal. My technique is to use a hole saw and keep touching and withdrawing, very slow RPM, as once an initial break through is obtained the risk of distortion, drill grabbing, etc., is high. Although I did not do this, taping the inside with several layers of duct tape may be helpful, or have someone hold a thick board up to the inside surface to support it during the cutting process. Using the tape would also tend to catch some of the metal filings.
I think it may be easier to use something to allow a pilot hole in the roof... maybe even a small piece of masonite glued in place.....