DO NOT stick the hemisphere up from the bottom, scribe and cut!!! Ostensibly this is good advise but for those who have learned the lesson "measure twice cut once", it might prove disasterous. Also a bit of knowledge about the CF flanges is in order.
The CF weld flange is stepped for a weldment. The lip protrudes out only so far (~ 3/16"). If you come up from the bottom of the flange, you are on the thickest portion. Scribing and cutting at the lip level will, indeed make the system much closer to a sphere, but the cutoff hemisphere will now fall through at top and not rest on the weld lip! Ouch! Some solid geometry investigation and equation fondling might be a bit better to determine the cut plane on the hemisphere.
Frankly, like Jim, I wouldn't worry about the egginess. I am proceeding this way with Fusor IV. It will make for a special egg shaped ionizer grid, but that design is a snap and doesn't involve the geometry calcs.
Neat freaks and perfectionist worry warts can spend the dough and the time to hit absolute spherocity.
Richard Hull
Created on Tuesday, January 09, 2001 6:42 PM EDT by Richard Hull