O'Hanlon's book on vacuum technique and Coplan's book on scientific instrument construction both talk a lot about welding and joining for vacuum components. As Richard Hull has mentioned, both pieces should be of similar thickness. If one piece is significantly thicker than the other, a weld lip should be machined on the thicker piece. The weld should be on the inside surface if possible. If not, the weld should fully penetrate the material to avoid leaving voids and potential virtual leaks on the inner surface. The weld should be allowed to cool down fairly quickly to avoid carbon migration.
Both references I have mentioned above have helpful "do" and "dont" diagrams to illustrate the proper setups for welding or brazing. I just checked last night on the web, and used copies of the O'Hanlon book are fairly abundant. I have also been able to snag a clean copy of the Coplans book, though I believe it is out of print. Both are valuable references.
Created on Monday, May 07, 2001 5:09 PM EDT by Richard L. Hester