A blocking arrangement for preventing the elevating table from moving includes a platform with four threaded stems extending downwardly from the underside of the platform. Each threaded stem has a threaded member and a chain wheel screwed thereon. A chain is trained about the four chain wheels so as to drive the chain wheels and the threaded members to elevate the elevating table. A brake wheel is securely mounted to the chain wheel of one of the threaded stems. The blocking arrangement includes a stop block which is movably connected beneath the elevating table so as to be in contact with the brake wheel to set the predetermined height of the elevating table to prevent any movement due to vibration.