1,078,327. Seaming and folding edges of non- metallic sheet material. R. G. E. DURAT. April 22, 1965 [April 30, 1964], No. 17006/65. Heading B5K. [Also in Divisions B8 and F2] Overlapping edges of sheet material 1, e.g. cardboard, previously coated on one face with a film 2 of thermoplastic resin, are joined by cutting a chamfer 4 through the thickness of the sheet material 1 alone along that edge thereof which is to form the inner portion of the lap joint, folding the chamfer 4 away from its coating 2 and effecting the joint by welding this folded portion 24 against the inner coating 2 of the outer overlapping edge 25 of the joint. To effect the chamfering, the coated sheet A is positioned with the coating 2 upwards and held by a natural or synthetic rubber block 5, Fig. 5 (not shown), on a lever 6 rotatable about a fixed pivot 7 on which is mounted a fixed support 8 through which extend screws 9 screwing into the lever 6. A spring 10 on each screw 9 forces the block 5 against the sheet A. A rotating cutter 12 chamfers the edge 3. A blade 13 is provided to clean the cutter 12. The edge 3 is folded at right-angles away from the coating 2 by apparatus, Fig. 6 (not shown), comprising a lever 14 pivotable about a fixed pivot 15 and having pivotally connected thereto an arm 16 pivoted to a slide 17 movable in a slideway 18. A right-angled crank 19 having one arm 20 terminating in a bevel 21 is secured to the slide 17. When the lever 14 moves from position B to position C the bevel 21 folds the chamfer 4 away from the coating 2 and a heated blade 23 penetrates into the fold thus formed to impart rigidity thereto.