The sieve shaker apparatus shown in FIGS. 1, 2, and 3 comprises a stationary or base frame 12 having a pair of vertical upright members or support columns 14 at its rear. This frame is provided with threaded adjusting feet 16 at each of its lower corners for leveling the apparatus. A substantially U-shaped housing 18 having opposite parallel side panels 20 and 22 may be provided to enclose the two sides and back of the base 12. The front opening may be closed by a hinged door 24 to provide access to the interior when loading and unloading a stack of screen trays 90 for a screening operation by the apparatus. The top may be closed by a cover 26 having a hinged door 28 for accessibility to the sieve shaker unit when supplying the screens with samples of aggregate to be separated. The doors 24 and 28 each may be provided with a handle 30 for convenience in opening and closing them, and fastening means such as clips or permanent magnets (not shown) may be provided to hold these doors 24 and 28 against their openings.