Abstract: A duplex filter cloth for chamber type filters has two initially separate pieces secured together, as by stitching, around circumferential terminal edges of turned-down collar portions of the respective pieces, which portions are closely and smoothly interlapped to provide a barrel neck for the duplex filter cloth. Turning down of the collar portions is accomplished by an elongate conical mandrel of a jig press which operates relative to mandrel-receiving openings in pairs of bed plates, inserted in turn in such jig press, to effectively turn-down circumferential marginal portions of filtrate feed openings of respective flat filter cloth sheets.