Abstract: The invention provides that a sewing machine is used for sewing the adjacent edges of a flat felt web which is folded to bring the edges together. The web moves past the sewing machine, and the sewing machine is mounted so as to reciprocate in a forward stroke in the direction of the web during the stitching, and to move rearward back to an initial position to effect the next stitch. The drive mechanism of the sewing machine is such that from the commencement of the forward stroke the machine is accelerated up to the speed of the web the needle penetrates the web and effects the stitch, the needle is removed from the web, and then is decelerated to zero before completing the backstroke. The invention also relates to an optical sensing mechanism for examining the presence of stitches.