Two tiny little copper Yo-yos took a bit more effort than you might think to make, so I thought I'd give a summary of how it was done.
Shaping The Hemispheres
I started by annealing 24g copper sheet and cutting 4 discs. Annealed 24g doesn't take much to punch out, so you don't need the fanciest disc cutter(yes, I am making excuses for that cutter. My nice one is in the shop.).
Next, I shaped the discs into domes, not quite full hemispheres, in my dapping block.
Soldering the Spheres
The soldering was pretty simple, using hard solder chips on the inside of the domes and doing all 4 at the same time. Each piece was then cut out with a jewelry saw, filed, and finished.
Finishing the Yo
I used a tube cutter and a miter to square the tiny tube ends. To keep the spheres aligned during soldering, I used pins and small amounts of easy solder chips. This part was the only real challenge, flowing the easy solder to join the tube ends, while not unsoldering the spheres themselves.
One downside to the final soldering step is that the whole piece becomes annealed again just before final finishing. For this design it's not a big deal, just requiring a bit more care when finishing to avoid denting or bending the center tube. A tumbler could be used to harden the spheres, but the center tube would remain a bit soft.