Method and arrangement in connection with production line for optic cable

An arrangement in connection with a production line for optic cable, wherein optical fibres (1) are arranged to be guided from starting reels (2) to a coating point (3) comprising feed means for feeding filling gel around the fibres, and extrusion means (3a) for forming a loose tubular casing around the fibres and the filling gel, the arrangement comprising a tubular device (4) through which the fibres are guided to the coating point, characterized in that the tubular device (4) is formed from three parts (4a, 4b, 4c) that are at least partly arranged within each other, that the front end of the tubular device (4) guiding the fibres is supported at the first part (4a) on a first base (5) moving in the travel direction of the fibres, that the front ends of the second and third parts (4b) of the tubular device (4) guiding the fibres are supported on a second base (6) moving in the travel direction of the fibres, that sensors (7, 8) are arranged in the first and the second base (5, 6) for measuring the force acting on the bases (5, 6) in the travel direction of the fibres, and that the arrangement further comprises means (9) for calculating the difference between said measured values for determining the friction force between the fibres and the tubular device (4) guiding the fibres.