Originally Posted by
cwilliamrose
The other side of this is that gaps leave an exposed edge which the welder may try to protect by using less than sufficient heat. The weld gets wider because there's a gap to bridge but the penetration is not improved, it only looks that way because of the filler coming through the gap on the back side of the mating tube. The penetration on the 'main' tube (for example the longeron) is not enhanced in any way due to the gap being filled. The only way to get good penetration on both parts is to use the proper amount of current and good technique. Machine setup, tungsten grind, etc all play a role as well. Simply providing a gap does not insure a good result but can and usually does create more distortion in the finished weldment. There are no shortcuts to good welds and tight fits do not cause poor welds.
I agree that the bushing used in this mount is too thick walled and that extra metal serves no purpose. Getting enough heat into that bushing while dealing with a poor fit would be quite difficult.