An improved horizontally-oriented machine capable of forming a trays or other similar fiberboard containers from single blanks. The improved machine includes three distinct sections: (1) a loading bay which includes a vertical lift, a sheet feeders and a unique set of gates for pre-positioning the end flaps of container blanks for later folding; (2) an adhesion and flap-folding section which includes adhesive applicators, a series of folding plows and a compression area for pre-folding the end flaps of the container to be formed; and (3) a final forming section including an adjustable vertically mounted mandrel surrounded by adjustable forming plows for making the final container. The flap-folding section includes a flight chain assembly which can be easily lowered when the machine is not operating, to allow service access to the interior of the machine in the event of a jam or misfeed, thereby avoiding the time consuming task of cutting or tearing out the misfeed, and allowing the machine to be quickly brought back on line.