A releasable pen block guide for releasably holding the pen block carriage of an X-Y plotter against the track during horizontal traverse movement. A first pair of wheel sets disposed in 90.degree. relationship are rigidly attached to one side of the pen block so as to guide the pen block carriage along the track when held in contact with one of the edges of the track. A pair of second, double, bogey-mounted wheel sets similarly aligned are carried by the pen block carriage and adapted for movement between a first position in contact with the other of the edges of the track and a second position out of contact with the other of the edges of the track and spaced from the first wheel sets sufficiently to allow the pen block carriage to be removed from the track. The second wheel sets are mounted to respective ends of a leaf spring extending outwardly from the pen block carriage in opposite directions along the edge of the track and parallel thereto, wherein the second wheel sets are bogey-mounted to the outward ends of the leaf spring for pivotal movement between the first and second positions.