How do you set tiny stones in an openwork cage without them falling out?

I've done a bunch of openwork cages and the answer is almost always the same: you need some kind of seat under the stone, even a minimal one. Prongs alone pushed over a girdle with nothing behind will always feel sketchy, expecially at 3mm where the prongs are barely grabbing anything. The trick is that the seat doesn't have to kill the airy look. Instead of a full plate, I cut a thin ledge or a couple of little notches into the inside of the cage wires right at the height where the girdle sits. The stone rests on those tiny ledges, and from the front you can still see light coming through the cutouts around it. You only need a fraction of a millimeter of contact under the stone for it to feel solid. Another option is a very small cup or dished disc, drilled with holes so light still passes through, soldered in behind the stone. Drilled plate sounds heavy but if you pierce it with a pattern it reads as part of the cage. On the soldering question, garnets and rubies can actually tolerate heat better than people assume, but I still wouldn't risk it. My usual order is: build and solder the cage completley, set the stone last. With a seat under it, setting after assembly is easy becuase the stone has nowhere to go. Push the prongs over with a pusher rather than a burnisher at first, then clean up with the burnisher once they're gripping. Trim the prong tips short and round them, long tips flex and that's often why things feel loose.

If a stone ever does need to go somewhere you can't reach with a pusher, you can set it on a short section of fine silver wire and solder that little assembly in as a unit, since fine silver moves easier and takes the burnish better. The tap test against your palm is the right instinct, by the way. If it rattles now it'll rattle worse after a week on an ear. Add the seat and you'll stop worrying about the carpet.

I tried something like this with tiny glass beads in a wire frame I made and everything kept sliding around while I worked, so I ended up stuffing a bit of that tacky blue wax stuff under the stone just to hold it still while I bent the wires over. Worked okay-ish but the beads weren't precious so I wasn't too fussy. When you're pushing those little metal fingers down over the stone, how do you even keep it from popping out sideways while you work? That's the part that scares me more than the finished piece.

I've had good luck making the seat out of the cage wires themselves instead of adding a plate. Flatten the bottom inch or so of each wire with a riveting hammer before you solder, so you get little paddles about a millimeter wide sitting right where the girdle lands. Four of those under a 3mm stone is plenty, and it reads as part of the design rather than some hidden shelf. I did this on a pair of aquamarine drops two years ago and the stones have never budged, even with one earring getting caught in a scarf and yanked around.

Update: took the advice about flattening the cage wires into little paddles and reworked both pairs. The stones sit on those flat spots now and the prongs just keep them from tipping, no hidden plate needed. Tapped them hard against my palm over a towel and nothing moved. Still get light coming thru all the cutouts like I wanted. Rubies went in last and they look great.