A substrate plating processor has a vessel on a support structure and a head support fixed in place relative to the support structure. A head having a rotor is attached to the head support. A lifter associated with the head support moves the head into and out of engagement with the vessel. An alignment assembly attachable to the rotor has at least one sensor adapted to detect a position of an inside surface of the vessel when the head is engaged with the vessel. The sensor may be a physical contact sensor positioned to contact the inside surface of the vessel.