Originally Posted by audioaficionado
How do you prevent the solvent glue from melting and clearing up the frosted surface of the half sphere?
That was a problem. Weld On #16 is pretty viscous, so it doesn't flow like the almost pure solven glues do. I put a bead of the glue over the end of the tube, working as fast as I could to beat the time it takes for it to skin over. Then I grabbed the half sphere and quickly put it in place (about 1/64" off, but that isn't a problem). The glue didn't run, and grabbed the pieces quickly. After about 5 minutes I ran a bead of glue around the joint, and let that cure for 30 minutes, then ran another bead. After an hour I tested it by weighting it with a fingernail clipper and stuck it into a glass of water. I checked for water inside every half hour or so. No leaks!
I knew this part was going to be difficult, so I bought 3 of the half spheres (45 cents apiece). I was lucky to make it work in two tries.
It is interesting to see what the optical effect of a half sphere is. It seems to act as a lens, as it has to, but it collects light over a large area and concentrates it into a circle about half the diameter of the sphere. With the flat side frosted it diffuses the light so there is just barely an image visible through it.