An accumulator device with a downward angled input transport (42). Downstream, an accumulating receptacle (44,47) receives sheets. The accumulating receptacle has an upper guide (47) and a lower guide (44) forming a horizontal accumulating channel. Dump rollers (43) act as a stop during sheet accumulation, and as a transport for removing completed accumulations from the sheet accumulating device. A rear portion of sheets (1) buckle downward into a trap arrangement (45) below the input rollers (41). Preferably, the upper guide of the accumulating channel comprises a continuously rotating belt (47) to urge accumulating sheets against the dump rollers (43). Also, a positive air device (49) may be used to assist in the buckling of the rear portion of the sheets. To assist in handling large collations, when a sheet arrives at the dump rollers (43) they advance by a small predetermined incremental displacement slightly shingling the sheets (1) to maintain positive control for later reliable discharge.