The rake classifier consists of a tilted tank with a rake-like scraper inside. The Dorr rake classifier on display uses two scrapers instead of one. The scrapers move back and forth in the tank, always rising in the upper position and going back down in the lower position. The movement of the scrapers is controlled by an eccentric wheel. The scrapers move the larger and heavier material settled to the bottom up towards the open edge. The lighter and smaller material remains circulating in the tank and exits through the overflow through at the lower end of the tank.

As early as 1928, when industrial concentration began in the old concentration plant, the Dorr rake classifiers were used in the secondary grinding circuit.