Abstract: The invention provides that a strip of flat steel is formed at its edges with channels which face in opposite directions and the strip is perforated between the channels. The strip is spirally coiled into tube form and a flange of one of the channels engages in the other channel and the adjacent flanges are crimped to form a helical seam in the finished tube. The tube is cut to lengths and the lengths are used in filter elements. The channel flanges are deformed prior to spiralling to facilitate the crimping and the spiralling is enhanced by the use of forming plates having edges which helically follow the curvature of the mandrel leaving a gap for the material so that the edges fit in one of the channels holding the edge of the strip captive until the strip is coiled and the captive edge is properly presented into the other channel. The machine provides a novel form of cutting head for cutting the tube to lengths, embodying a cutting tool which orbits the tube in performing the cutting.