An aligning fixture for box welding that is used to internally support a work-piece has a mounting plate and a plurality of supporting legs. Each of the plurality of supporting legs is removably attached to the mounting plate by a plate connector in order to provide adjustability for welding work-pieces of various sizes. A support structure, being a first leg and a second leg, is pivotally connected to the plate connector and a hinge. The hinge supports a roller mount, a roller, and a pad assembly. The roller mount is vertically positioned, wherein the roller is connected to the roller mount opposite the hinge. The roller allows the supporting leg to slide across the bottom surface within the work-piece. The pad assembly is pivotally attached to the hinge and rests flush against the inner wall of the work-piece when the aligning fixture is deployed.