@Brook_Drumm , the bed I was referring to was on an original PB Plus, and I remember discussing it with you at San Mateo Maker Faire years ago. Looking back, I was trying to manage a couple of constraints: I wanted the heat flux to be fast since I was using 12V, and the current was near the limit. Also I didn’t want to wait a long time for it to heat up. So I started with 1/4" material and machined away about half of that thickness for the pocket. I too thought the rib around the edge would be beneficial. I also cut a channel and a round recess in the center of the pocket, and epoxied the thermistor there. This created a really thin spot in the center of the bed. @Kyle1 , you may have way better luck than I did since you’re machining relatively less of it away than I did.
The major benefit of this was the consistency of the heat was fantastic. But I think this thing was really on the edge of what could reasonably be done on 12V. If I wind up building something with big heat via an SSR, I might try Mic 6 again, but I would sandwich the element between two pieces with through hardware and try flipping the bed occasionally. I would also be very careful not to over constrain the bed. As you said, aluminum moves when you heat it!
it’s faster!