Abstract: An improved door mounting system which uses a pair of channel members directly coupled to a guide member to allow an access door to move from a position closing an access opening to a position clearing the access opening. The door can be a single panel or a number of hingedly interconnected panels. The door is movable laterally into a position or vertically. The door does not "swing, but it "slides", shifts or moves relative to and along the walls in contact with the ends of the panels. The particular door assembly of the present invention is for solving the following geometric problem: finding the geometrical locus of a center of a straight line segment when two ends of the segment are forced to move along two perpendicular straight lines.