Abstract: A tool positioning system comprises a discontinuity detection means, such as an eddy current system, for detecting a discontinuity within a workpiece resulting from a joint between a first piece of material relative to a second piece of material, the discontinuity being detected from the back side of the second piece of material. The discontinuity is detected at a plurality of points by translating an eddy current probe over the back side of the second piece of material, the individual points thereafter being utilized to compute line elements that define the joint between the first and second pieces of material in a continuous fashion over the surface of the second piece of material. Thereafter a tool, such as a laser welding tool, is guided along the computed position along the backside of the second piece of material such that the first and second pieces of material are welded together along the joint.