Originally Posted by
Cassius
Doug: So wall thickness isn't the real issue, it's the tempered steel that's the problem? (Due to the odds that a rookie won't be able to control the temp good enough)
It is true that it is more difficult to control the heat on thin wall tubing so the joint doesn't get too hot. But the other more challenging problem is applying even heat so the frame doesn't warp and get out of alignment. You need to use a pattern that minimizes warpedge while at the same time making sure the joint doesn't get too hot. Just to be clear, heat will bend a tube to the side that is being heated so you have to figure out how to correct for that. The easiest way is to bend the tube back after it has been brazed. Of course while that is possible, it isn't the best method. However thin wall heat treated tubing doesn't bend like old Reynolds 531 and it might buckle instead. The other option is to just leave it crooked.
Accurate frame alignment involves a number of factors that begins with good miters and includes placing the spots to keep them together in the plane of the frame. In addition you have to consider the sequence of how to braze the frame together. After you have taken those steps you need to follow a heating pattern that minimizes distortion when brazing each joint. These complications are why everyone is suggesting that you use heavier non-heat treated tubing that absorbs brazing mistakes better and can be bent back into alignment after each joint has cooled.