A system for forming bends in a portion of a tubular work piece includes a roller assembly having rollers. The work piece is supported such that the portion thereof is aligned with the rollers along an axial direction, and such that the work piece can be advanced in the axial direction. At least some of the rollers are guided along a path around the perimeter of the work piece, such that a pressure exerted by the rollers on the work piece increases from a minimum value to a maximum value along a first half of the path and decreases from the maximum value to approximately the minimum value along a second half of the path. The system includes an adjuster assembly for moving the roller guide structure along a direction that is inclined relative to the axial direction, for varying the maximum value of the applied pressure.