here be are building an angle steel box frame that will contain a box or whatever

Step 1: Cut the Angle Steel With Cold Saw

the angle iron needs to be cut with a special orientation so that it doesn't hop/catch/ or bind. see second picture you need to orient it so that the flat part is orientated to be facing you.

Step 2: Mitr Cuts

so we are going to use the cold saw again. first we set the saw to right to bottom left 45 degree cut. now we are going to cut right on the tip of the corner of the angle steel using the same anti bind orientation as before. we are only doing one cut per piece as the next cut will be from the other orientation. make sure that were you and going to cut is going to support the box which means that all pieces with the bottom support piece is facing in and will the other piece facing up

Step 3: Weld It Together

now you might want to weld it from the bottom to allow whatever you put in there to sit flat. or you can weld it on both sides and just grind the side flat were the box will sit. if your gap is a little big to weld you can use the angle and cut it at the same alternating 45 degree angles but it will no longer have square edges. I did have a edge that needed to be longer but on everything else I just bridged it with a weld.