The aluminum tubing was secured through a local industrial supply company that sells remnants to the public. I spent about twenty minutes digging through their stock and scored 3 feet of the 4" OD and 2 feet 5" OD tube for about $25. I was thrilled with scoring both the same day (their stock continually changes). The wall thickness on the 5" is beyond overkill, but I couldn't beat the price given what you can pay through online suppliers. I cut both of them to the appropriate length (approx 15 3/4" for the 4" OD and 12 3/4" for the 5" OD respectively) at home. I used a miter saw with a standard carbide tipped blade to get perfect square cuts. I don't recommend or suggest for someone to attempt these cuts without previous aluminum working experience. So, I won't document or show pics on how to cut such large pieces on a miter saw. But, it can be done with the proper jig and technique.
The hemispheres are from King Architectural Metals:
http://www.kingmetals.com/Catalog/Catal ... tailId=228
$3.00 for the 4" and about $5.00 for the 5" hemispheres. I went with steel because it is considerably cheaper compared to aluminum. The weight difference was about a pound or so at the most, so I voted with my wallet.
As far as attaching each hemisphere, I used .125" thick .5" aluminum bar stock. Do not purchase the crap they sell at a big box store. Their aluminum stock is garbage; any attempt to put even the slightest bend will cause it to snap. Trust me on this. I cut 3" strips on the miter saw and then attached them to the cylinder using .125" rivets. I used a .244" drill bit to countersink each .125" pilot hole. It lets each rivet seat below the curvature of the tubing, making filling each hole a breeze.
I put a slight bend in each strip to account for the curvature of the hemisphere. I then drilled the corresponding countersunk holes for the hemisphere, making sure that everything was properly lined up.
At this point, it would take some considerable effort to remove the hemispheres (I loathe drilling out steel rivets). After attaching the other end and giving it a quick hit on the belt sander, the results are as follows...
That's the current state of progress for now. I hope to periodically update as I continue, but we know how long that can take....