The purpose of this study was to develop a device to separate stones and other accompanying impurities from milled and paddy rice grains. Separation was accomplished using a combination of oscillating sieves and a variable directional air stream.Three sieve sizes with oval shapes having lengths ranging between 4.55 mm and 6.75 mm and aperture thickness between 2.25 mm and 3.35 mm were used. The reciprocating sieves performed effectively at crank speed of 160 rpm. The machine effectively removedall chaffs and other light impurities from both milled and paddy rice. The machine also performed satisfactorily in removing nearly all the stones in the rice samples. From the performance evaluation of the machine it was observed that 874 kg/h of milledrice and paddy rice could be processed. Although this work did not cover the effects of sieve size, sieve agitation on machine capacity, one could suggest that the capacity of this device could be increased with the use of proper sieve size, sieveagitation and air direction. Tray loss was 2.99 for paddy rice and 17.81 for milled rice. The average separation efficiencies of the machine for paddy and milled rice were 97 and 82, respectively.
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