Ken, Don't waste your time building a special table on which you can weld/braze. An ordinary common red brick on top of anything will do and probably be better than anything you can dream up. What you have to be careful about is that the pieces being brazed, silver soldered, together are clean, there is a sufficient volume (not temperature) of heat available, and that a borax type flux is used. Another important point is that there should be some way to steady the pieces being joined so that they don't move around during the brazing process.
Arthur Mexico City
