the assembly 26 each comprise a multiplicity of control arms such as the arms 36 and 42 and since each arm and its associated feed rollers are substantially identical and operate in the same manner only one such control arm i e a lower arm 42 is illustrated and described hereinafter in connection with fig2 through 4 referring to fig2 each control arm 42 comprises a flat plate having a substantially rectangular configuration the plate preferably being constructed from metal such as aluminum so as to minimize its weight the feed rollers 38 and 40 are also formed from metal such as aluminum pressed onto the outer race of a respective bearing 66 67 having the inner races pressed onto a respective stud shaft 68 69 secured to the arm 42 so that each feed roller 38 40 may freely rotate relative to the control arm 42 as illustrated each roller is mounted with its periphery projecting slightly beyond an elongated edge 70 of the control arm so that it may engage the respective drive roller 58 60 when and as desired as hereinafter described the amount of projection of the periphery being such that engagement with the drive roller will not occur until desired fixed on the control arm 42 adjacent to and above each roller and superposed over the edge 70 is a respective guide member 72 73 each guide member having a substantially rectangular configuration but truncated to have a lower portion with a pair of joining concave edge surfaces 74 75 thus the guide member has three straight edges and a pair of adjoining arcuate edges the contour of the surface 74 corresponds substantially to that of the periphery of the feed rollers 38 40 while the contour of the surface 75 corresponds.