<p>A workpiece-treating machine having a table with a pair of longitudinal edges and a working station between the edges has an apparatus for positioning a workpiece in the station which in turn has a generally square section metal tube extending along one edge of the table and formed with a longitudinally extending inner T-slot to which the one edge of the table is secured by T-fasteners, a pair of transversely spaced but longitudinally extending and upwardly open outer T-slots, and a pair of outwardly open and longitudinally extending outer T-slots. A longitudinally extending guide rod is supported at the one table edge by supports and T-fasteners that fix the guide rod on the table in the outwardly open T-slots at the one edge in a position extending parallel to the longitudinal edges. A carriage longitudinally displaceable along the guide rod is fixed to one end of an elongated traverse extending transverse to the longitudinal edges. A stepless-adjustment clamp on the carriage has a T-fastener engaged in one of the upwardly open T-slots for clamping the carriage on the tube at any position therealong and a toothed retaining element on the carriage engaged in the other upwardly open T-slot can arrest the carriage at any of a plurality of longitudinally offset positions therealong.</p>
