the frame 12 and is rigidly connected with a horizontal fork 214 each arm of which has at its tip a roller 216 the fork arms and the rollers are so located that they enter between the flanges 200 and 202 whereby the rollers 216 216 will encounter one flange or the other as they move up and down with the platform 210 a vertical drive screw 218 is centrally mounted and is journaled near its opposite ends and prevented from moving axially by the subframe 206 the screw 218 is threadedly connected with the platform 210 for lowering and raising motion thereof as the drive screw 218 is rotated the upper end of the drive screw 218 is connected with a flexible rotating drive cable 220 which at its other end is connected with a hand wheel 222 located at the upper center of the machine near the operator 39 s handle 28 a power drive assembly 224 is mounted upon the upper surface of the frame 12 and includes a power source such as the internal combustion engine 226 and fuel tank 228 and speed reduction gearing 230 as seen in fig1 and 2 the gearing 230 is arranged on the longitudinal centerline of the frame 12 and has an input pulley 232 driven by a belt 234 from an output pulley 236 of the engine 226 a suitable adjustable belt tightener 238 is.