After thinking about the distortion caused by the riveting, I decided to try machine countersinking these holes rather than dimpling. Here is my sample with countersinks on either side of the hole.

I squeezed a rivet. This looks a lot better. I'm going to get some soft rivets. I bet they will allow the shop head to fill the countersink.

Here is the lid with the (soon to be) aft wedge bonded on. This needs sanded smooth.

After sanding the excess epoxy away, I planned to mixup a batch of micro. I'm hoping to use this little container of microballoons from the place I used to work. This sample container has microballoons from Trelleborg...they use them to construct subsea buoyancy which can withstand deep ocean pressures.

Also, the epoxy shown here is what I have available for quick curing epoxy. It's 15 minute expoxy from a hobby store back in Ohio. Actually, I don't even know whether the store exists anymore. I probably purchased this epoxy at least 25 years ago. The hardener has gotten really thick...so much so that it doesn't run down to the spout when the bottle is inverted. I have it warming up in this photo in a glass of hot water.

So, warming up the hardener worked. I measured out a gram of resin and hardener and mixed it up, then added the microballoons. Considering that I'm using nonstandard microballoons as well as ancient epoxy, I decided to just let this first batch cure on a piece of cardboard to make sure all is OK.

Umm, yeah...I'm glad I didn't smear that first batch on my part. After 3 hours, the blob (the one in the back) was still a bit tacky. I mixed up another batch...this time with more hardener. Instead of 1:1, I mixed it 1.4:1. Unfortunately, that batch didn't really cure very well either. I think I'm going to dispose of this old epoxy at our local hazardous waste facility. I found a kit of West Systems G5, 5 minute epoxy on Amazon and ordered that.