Welding captive nuts and filling holes on the frame

The rear subframe had a few holes drilled in it for unknown reasons (but probably alarm related) by previous owners. I decided I disliked them sufficiently that I should try filling them with weld. 

There was a large diameter (c. 13mm) hole in a cross-brace with the VIN plate and a small hole next to it, probably for a self-tapping screw. I scraped off the sticker then ground the rust from the hole perimeter with a mini grinder. 

 Next came the MIG work. It went pretty well, carefully adding bead to bead with enough time to cool between each burst to stop the whole thing from dropping through. It only needed a few seconds between each bead for this. Finally, a flap wheel on an angle grinder restored the level of the material. There are a couple of little imperfections in the surface but rather than risk sorting them with more weld, I decided they'd fill with primer easily enough. 

The other welding I needed to do was to restore six captive nuts that had split away from the frame. Three were M8s for the exhaust mounting brackets, two M8s for the grab rail and rear fairing panels, one was an M8 for the left-hand rear indicator bracket, and one M6 for the right-hand rear fairing panel. The mini-grinder came out again to get enough shiny metal for me to weld to. This was very tricky as it turned out because of restricted access to all but the M6. In each case, I wound a bolt tight into the nut to ensure there was good electrical contact, then welded some wire into the frame near it, running up to the nut itself.

A captive nut - that's captive again!

Rear subframe after all welding
and grinding was complete.

Finally, I used a wire brush on a drill to bring all the rust off where it had developed. In most cases, these places were on factory frame welds, in the others it was nicks and scratches. I finished up with zinc primer, pending rubbing back on main spar sections and a coat of black.

Rear subframe after derusting and priming