Abstract: A tool including two flat parallel flanges (2 and 3), defining between them a space (4) which corresponds to the thickness of a cutting blade (5) and including two symmetrical slots which have profiles that are roughly identical to that of a gutter (7) so as to constitute a guiding cradle for cutting the gutter by operation of the cutting blade (5) between flanges (2 and 3). The guiding cradle is defined by slots delimited in an upper zone by a convex contour (6b) of a fixed part of the flanges, and in a lower zone by the concave contour (6a) of a movable part, so that a movable part can be articulated at one of its ends around a fixed axis of rotation (8) like a jaw (9) in the open position (0), to allow free passage of the gutter (7) and in the closed position (F) constitutes a fixed support for cutting.