The present invention relates to a portal to pivot (1), including: - a hollow upright (2) with the upper end (22) and lower (21) configured for guiding the riser in rotation about an axis connecting the upper and lower ends and having a first direction; - a hollow transverse beam (3) fixed on the hollow upright (2) and extending from the lower end (21) of this hollow upright according to a second direction perpendicular to the first direction; - an electric motor (4) housed in the hollow upright (2); - a transmission (5) including: - an endless screw (51) housed in the hollow transverse beam (3) and mounted to rotate in the second direction with respect to the hollow transverse beam, the endless screw (51) is driven in rotation by the electric motor (4); - a toothed element (6) mounted to slide relative to the hollow transverse beam (3), and meshing with the endless screw (51); - a guiding arm (7), comprising a first end (71) integral with the toothed element (6) and a second end (72) is configured in order to guide the arm (7) around an axis of rotation with the first direction and offset with respect to the axis of rotation of the hollow upright.
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