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Sorry, I didn't mean to suggest that you wouldn't have to remove any rivets to peel back the interior panels--you do. However, there are, IMO, four advantages to removing only interior rivets:
-They're easier to drill out, since they have "pilot holes" in them
-You can put back exact replacements with common tools
-You don't compromise the strength of the shell
-And best of all, you haven't created new opportunities for leaks
I would urge others to remove exterior rivets only as a last resort. You simply can't do as good a job of replacing them as the original work (unless you have the equipment).
The spiral saw is the tool used to cut openings in drywall and tile. The bit spins, but does not reciprocate. It is a lot like a laminate trimmer. I made a jig out of plywood to hold it at 45 degrees. It was two planes glued against a 45 degree wedge. I simply laid the tool flat against it and slid it along. The angle jig was butted up against a wooden strip that I screwed to the floor. This kept the cut straight. This arrangement gave me the freedom of movement to cut partly into the wood that was in the U-channel. A chisel and some grunting did the rest.
My U-channel was, well, a U-channel : ) The edge of the plywood could enter or exit only from one side. It was a close fit. In fact, I had to push in some bumps in the channel that were created when the assembler put staples through the channel and into the wood.
The channel was formed sheet aluminum. So, there was no rust, though some areas were noticably corroded. It went along the entire perimeter of the plywood, including the section where the frame was attached. There were "Vees" cut out of the inside of the curved sections.
The frame was attached via a different channel along the underside of the access panel. This channel faced up. It was attached to the inside and outside skins. It was the primary point of load transfer to the skin from the steel rib that spanned between the frame members. I would strongly urge you NOT to drill out the rivets that attach it to the outer skin.
I would draw a sketch, but I don't have a way to digitize it easily. Just think of three "U" channels. One faces in to and surrounds the edge of the plywood. One (steel) faces/opens down to the street and is welded at both end to the steel frame. One faces up and is riveted to the skins. Steel bolts go through the top of the down-facing U, the sides of the inward facing U, and the bottom of the top facing U.
The steel bolts were mostly rusted out, and the rest made big holes in the channel when they pulled through. I put some heavy (1/4" web) 1" Al angle into the the top facing/opening aluminum U. This was much thicker than the original and helped spread the load more evenly.
I know this sounds complicated, but it isn't. Go have a look at your unit and you'll figure it out.
One last tip--seal all of the new plywood with penetrating epoxy. Do the sealing after drilling holes, etc. This way, even if there is a leak--who cares?
Jon in SC
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