So I know when you but weld you want 100% penetration, I know what that looks like. But I'm curious, how do you know you have gotten 100% or at least good penetration, when welding a flange ? I know its not suppose to go all the way threw because it would mess the back site up. So what would you look for ?

 

Most flanges are not butt welds, they are fillet welds. In other words, 2 pieces that are 90 degrees (or some angle) from each other...NOT inline and on the same plane.

When doing a fillet weld, the general rule is to make the weld as large as the metal is thick. This will be overkill for your application if you have 1/4" material. All you will need is a beat that's about 1/8-3/16". Just weld it and don't worry about it.