Left and right frames are formed of a resin containing no glass fibers and bridged
together by a tray formed of steel, a chute formed of resin, and underbars formed
of steel. Each frame has a box-shape configured of a plate surface and side surfaces
formed by bending the edges of plate surface in a common direction perpendicular
to the plate surface, thereby preventing the plate surface from bending significantly.
When the tray and underbars expand, then the frames bend slightly to absorb the load.
