positioned so that the inner ends or beds 43a of shallow bed slots 44a are off axis i e are not coincident with pivot axis 30 in addition with the embodiment shown in fig1 the distance 41b from the transverse end member 24 to the slot beds 43a should exceed the distance 41a from transverse end member 24 to the pivot axis 30 thus as illustrated in fig4 and 7 the second ends 38a 38b of the grizzly bars 34a 34b respectively will drop within slots 44a 44b respectively to engage the slot beds 43a 43b respectively and adjacent bars 34a 34b will be differentially lowered as the frame 16 is raised while the horizontal separation distance 54 fig6 between grizzly bars 34 remains substantially constant the actual maximum separation distance 54b fig7 between adjacent bars 34 increases as bars 34b are lowered relative to bars 34a the actual maximum separation distance 54b between the centers of the bars is the product of the horizontal separation distance 54a between the centers of the bars and the secant of the angle 49 where angle 49 is the angle shown in fig7 between the plane 53 defined by the center lines of the grizzly bars 34b or alternatively bars 34a and the longest line 55 connecting adjacent grizzly.