I really wasn't going to use this dish, since it looked to be in such bad shape, but as it happened I decided to mount it on a pole and try it. I straightened it as much as I could, trying to get it back into something resembling the original shape, and came pretty close. A couple cans of Rust-Oleum Rust Reformer at least stopped the development of more rust on the worst spots while I decided what to do with it. As I sort of alluded to in my first post, I'm not particularly mechanically inclined, particularly when it comes to working with metal, but it worked well enough (probably at least as good as my 7.5 foot dish, and I know I can do some more tweaking to get it better) to try to do something to repair it.
The inspiration came when I was watching a syndicated home repair program that's transmitted weekly on one of the feeds channels. The guy in that show had to repair a support column with some rotted wood, not enough to replace the entire column, but after the rotted wood was removed there was still kind of a large hole. Now I thought he was going to use some kind of wood filler to repair it, but he used something completely unexpected: Bondo, a substance that is normally used to repair dents in auto bodies. He said that when it cures it's tougher than the original wood, and it sticks to just about anything. It comes in two parts, a white goopy substance and then a tube of some kind of curing agent. You mix the two together (there are several videos on YouTube that show you how to do it, just search for Bondo). It is not like epoxy where you mix equal parts, instead you knead the tube of curing agent and then use just a small amount compared to the amount of Bondo. You then mix them together completely. I do suggest watching at least three or four of the videos since they show you how to do it, and more important, what not to do (don't use too much curing agent, and don't mix it on cardboard or any kind of paper-based surface).
Since Bondo was originally intended for use on metal, it dawned on me that it would be perfect to repair the rusty rim - after all I was going for strength, not appearance. The hardest part of the repair was keeping the Bondo from running down off the metal, since I probably applied a little too much and it is a bit runnier than you would think. Ideally you apply it in ¼" layers but if you are impatient and try to apply it a bit thicker on a vertical surface or someplace with no support underneath, it will tend to sag or drop off after a bit. The solution is go in your kitchen and grab a box of waxed paper, and use pieces of wax paper to hold the Bondo and roughly form it the way you want (the waxed paper will release cleanly after the Bondo is cured enough to be firm). Even then you will probably still need to go over it a few times to fill in the gaps. Here is the result after a coat of black spray paint was applied, it's not pretty but I was going for strength and rust repair, not looks:
An auto body worker would have the tools to sand it down nice and smooth, and make it look like the original rim. I don't have such tools, so I used a surform-type device (a round one that attaches to a power drill) to take down the worst of the high spots, and then just painted it. I applaud you guys that have the patience to make stuff look like the original, but I don't, and the goal here was to keep the rest of the rim from totally rusting away.
One thing I did not do, that you are supposed to do, is sand the original surface down to bare metal. I did not do that for a couple reasons, one is that I had painted it with the Rust Reformer, which converts the rust to a black substance that I really didn't want to remove. But the other is that it would have been nearly impossible to get all the paint off anyway, given the original condition of the frame (how would you get sandpaper into all the cracks and crevices?). I figure that in this particular application it wouldn't matter as much, and so far that seems to be the case. If I were patching a somewhat flat surface like a car body then I would think it much more important to get the paint completely off, but here I was basically replacing part of the tube with Bondo, and it seems to have worked. The stuff seems really tough when cured, I would guess at least as tough as an aluminum tube, if not a steel one.
After getting the dish up onto the pole it became apparent why it rusted so badly. Most C-band dishes cover the ends of the support tubes in the center of the dish. This one didn't, instead they were left wide open so water could run inside during any kind of wind-driven rain or snow event. And, there were no "weep holes" anywhere around the rim of the dish. So I did two things to try and stop this from happening again. First, I drilled a small "weep hole" at the lowest point on the dish rim, so that collected water could drain out - and as soon as I drilled the hole, some water did come out!
The other thing is that on the back side of the dish, I plugged the ends of all of the downward-pointing tubes with Bondo.
I also tried to work some Bondo into the gap in the outer rim on the downward-facing side, just above the repaired section, so that water could not run down and collect just above the Bondo'ed section. What I was trying to do was make sure that any additional collected water has a path to escape, either through the weep hole or out of the gap in the outer rim. This may not be perfect (and I guess I'll know if any additional rust develops) but the real point is that this dish was poorly designed, or maybe poorly assembled, I am not sure which. If by chance you have such a dish, you may also want to drill a "weep hole" at the lowest point. Of course, if you plan on using a positioner arm to move the dish then the lowest point will vary depending on which satellite you have it pointed at, so in that case you may want to drill more than one. I'd also plug any downward-pointing open ends on the support ribs, if not with Bondo then with silicone caulk.
I'm not claiming this is the best way, or even the correct way, to repair such a dish but if you are like me and have almost no metalworking skills whatsoever, it's probably the easiest way. But before applying Bondo I would remove as much surface rust as possible, and then use some kind of rust converter product to change the remaining rust to something that is not rust. This may not last forever, but I'm pretty sure it will extend the life of the dish by at least a few years, and I can always use another C-band dish.
EDIT: Forgot to mention that I had removed the dish from the support ring, both so I could remove the rust and repaint the ring and mount, and because when we got the dish the mount was rusted so badly that we could not get it off the pole until we'd detached the dish (it's kind of a weird mount anyway, not like anything I've seen before, and also rather poorly made in my opinion). Anyway when I put the dish back on the ring I somehow managed to get it at a 90 degree angle from its original position, so that the rusty part of the ring was on the side rather than the bottom. This actually helped when applying the Bondo, because it was much easier to apply from the side than from the bottom up.