The pieces for the base frame are cut from 1x2x.090  wall rectangular steel tubing.  (Photo 1)

 

 

 

 

 

A bird’s beak notch is cut into the inside of each rail to make a bend in the  fame.   (Photo 2)

 

 

 

 

 

Side rails are bent at the notch (see arrows in photo)  and the perimeter pieces of the frame are aligned and clamped together for tack welding.  Note the plumb line used to insure the front, center and rear cross pieces are all on center.   (Photo 3)

 

 

Final welds complete the frame base. (Photo 4)