A seed potato cutting system includes a cutting roller unit, including an endless roller chain, having a plurality of parallel roller sets with longitudinal gaps therebetween, configured to convey seed potatoes resting in the gaps in a longitudinal direction through a plurality of pairs of upright cutting blades, a laterally-slidable thumb rake, disposed in each longitudinal gap parallel to the roller sets, having a plurality of upwardly extending thumbs, and a thumb rake alignment device, configured to sequentially laterally slide all thumb rakes in first and second directions, respectively, to contact and laterally align each seed potato with a corresponding pair of cutting blades as the roller chain conveys the seed potatoes theretoward.