I sold the 200-500 but this is on a Sigma 150-600. This was the first one I did and learned a couple things that made the 200-500 turn out better.
1) I drilled the 200-500 with my drill press. This was hand held.
2) secure the foot in a vice. Trying to hold the foot and drill was tough. On the 2nd one, I secured the foot in my drill press vice.
3) it is soft cast aluminum, drill a smaller pilot hole first so that the larger bit (5/16 for the rivet nuts I was using) doesn't want to bind as much.
4) I did a better job on the 200-500 at lining the hole up on the center line of the foot. The aluminum doesnt' work as well with a center punch as I would have liked. The drill press made it easier to keep the bit from walking when I drilled.
(because my bit bound up on exit, the rivet nut didn't seat totally flush with the lens foot to I had to file a little off. Looks ugly on this one but it worked. On the 200-500, I seated it slightly below the surface of the lens foot so I didn't have to do any subsequent filing.)
For the rivet nut, once I had the appropriate hole drilled, I mixed up some JB Weld (any epoxy will work) and smeared some on the nut before inserting into the foot to be sure it stays where I wanted it.
Just to test things out on the 150-600 before doing it on the 200-500, after the epoxy had cured for a day, I inserted a 1/4X20 bolt, clamped the head of the bolt in my 6" Bench vice and tried to pull it out. It was, and is) in there forever. The one I did for the 200-500 didn't even leave a shiny spot on the foot. When I sold the lens, the person who bought it said "wow, that's a great idea". Didn't hurt resale value at all and did make me feel more secure about it. 2 bolts coming loose is far less likely than one.
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