plurality of elongated upright shaft members includes a pair of externally threaded mandrels 227 having the respective remote ends thereof journaled to the cabinet 13 or to suitable frame structure as at 257 preferably utilizing bearing structure not shown like the bearing 67 for the principal embodiment the plurality of restraining members for this embodiment includes a pair of yoke elements 228 respectively including upper and lower internally threaded stabilizing control members 125 127 threadedly engaging the respective pair of externally threaded mandrels 227 from the above disclosure it should now be apparent to those skilled in the art that the alternate embodiment per se includes considerable duplicate structure i e the pair of threaded mandrels 227 the pair of yoke elements 228 and the pairs of upper and lower internally threaded stabilized control members 125 127 accordingly the disclosure herein for one of each of these duplicated structural components will be intended to be applicable to the other additionally each of the mandrels 227 is threadedly engaged with both upper and lower stabilizing control members 125 127 as clearly shown in fig6 of the drawings further each yoke element 229 is fixedly attached to the carriage assembly 221 whereby proper rotation of the mandrels 227 is effective to selectively raise.