Imprinting machine with wheel setting rack mechanism

A variable data imprinting machine comprising an elongated housing defining a substantially rectangular elongated flat printing bed providing a document supporting surface and having first and second sides, a print wheel pack formed of rotatable, coaxial side-by-side closely adjacent print wheels each having circumferentially spaced raised-number-bearing imprint block formations separated by notches about their peripheries for imparting impressions to a document on the document supporting surface, an imprinting carriage movable through advance and return strokes longitudinally along the document support surface having a roller platen for transfer of imprinted characters to the document during one of said strokes, an elongated rack case perpendicularly traversing said housing subjacent the wheel pack having a number-bearing rack control panel portion projecting beyond the first housing side, a plurality of flexible band-like toothed racks slidable longitudinally in said rack case with teeth of each of the racks engaging notches of the respective print wheels to rotatably index the print wheels to selected number-printing positions, the rack case having means forming plural elongated guide slot trackways therein sized to receive and guide the toothed racks therein for their longitudinal wheel-indexing movement, said guide slot trackways defining serpentine paths in top plan providing intermediate laterally closely adjacent path segments underlying and vertically aligned with the respective print wheels and first end portions cur therefrom laterally to form more widely spaced parallel trackway path segments underlying the control panel portion, centering means activated by movement of said carriage during a pre-imprinting part of its advance stroke and including a centering blade member insertible into centering grooves on each rack for precisely aligning the print wheels to ensure proper fine adjustment registration of the imprinting numbers at the printing positions, said centering means including a control lever in the path of movement of the carriage to assume active and release positions responsive to carriage movement, blade lifting means coupled to the control lever for raising said blade member into fine adjustment centering insertion into the grooves when the control lever moves to said active position upon movement of the carriage through said pre-imprinting part of its advance stroke and for releasing said blade member to return to its inactive position when the carriage nears completion of its return stroke, wherein said blade lifting means is a carrier plate pivoted for movement about an axis near and parallel to the pivot axis of the blade member and connected to said control lever to swing upwardly against the blade member for inserting the latter into the centering grooves when the control lever moves to said active position and to swing downwardly to a release position when the control lever moves to its release position, said blade member and centering grooves being shaped to cause the blade member to be cammed downwardly by manual readjustment of any of said racks from the fine adjustment positions produced by the last-preceding lifting of the blade member, and overcenter spring means for resiliently restraining the blade member in raised centering position inserted into the grooves following lowering of the carrier plate to its release position until one of the racks is readjusted.