Abstract: Apparatus for assembling plate and tube heat exchangers of the type having tube end portions joined to end plates includes a carriage for longitudinally carrying an assembled but unjoined heat exchanger. An upright stationary frame supports a tool holder for movement transversely of the heat exchanger longitudinal axis. The tool holder is movable so that tools carried thereby are located in facing relationship to an end plate for joining tube end portions thereto. The tool holder is also transversely movable to a clearance position for providing longitudinal movement of the heat exchanger and carriage therepast. A clamping device at the opposite end portion of the heat exchanger clamps the opposite tube end portions for holding the tubes against longitudinal and rotational movement while the other tube end portions are joined to an end plate. The clamping device is also movable transversely of the heat exchanger longitudinal axis.