to various components of the invention a vertically disposed support 26 is also secured to the support 18 and has a vertically disposed gear rack 28 associated with a channel 30 into which a vertically adjustable device 32 may be positioned in a vertically adjustable manner the device 32 includes a flat bar 34 which is received by the channel 30 with the gear teeth 36 and 38 extending laterally therefrom which are selectively movable into contact with the gear rack 28 by means of the vertically movable actuator 40 bracket 42 is secured to the lower end of bar 34 and extends therefrom and has a hollow bushing or opening 44 formed in the outer end thereof the numeral 46 refers to an elongated second support having an inner end 48 and an outer end 50 the support 46 is channel shaped in cross section and has a pair of longitudinally extending grooves or channels 52 and 54 formed in the interior thereof the inner end 48 of support 46 is pivotally secured to the bushing 44 by means of pin 56 which extends through the inner end of the support 46 and through the bushing 44 the numeral 58 refers to an air motor having a drive shaft or power shaft 60 extending inwardly through the opening 62 formed in support 46 with the motor 58 being secured to the support 46 by any convenient means a pulley 64 is mounted on the shaft 60 within support 46 for rotation therewith and has a drive belt or cable 66 extending therearound a pulley 68 is also mounted in the interior of support 46 at the outer end of the support 46 and is rotatably mounted on the shaft 70 with the cable 66 extending around.