Abstract: A swivel head swivels on its support along a plane face that is perpendicular to the axis of rotation. The face has the shape of a movable disk that slides on a stationary disk. The movable disk is rotated by means that ensure centering with a predetermined clearance. The stationary disk is pierced by two diametrically opposite bores and the movable disk is pierced by at least one pair of diametrically opposite bores with the same diameter and with the same distance between centers, and located at the same distance from the center, within the clearance. The positions of a pair of bores may be generated from those of another pair, by rotation of predetermined angle. The support features means for inserting, across the two disks, two expandable rings, for expanding them, and for retracting them.

Abstract: A spindle head can rotate on a support about an axis which forms, with the working plane, an angle .alpha. which advantageously equals 35.degree. 15'52"; the angle between axis of the spindle itself and the axis of rotation of the head is the complement of angle .alpha.. The projection of the axis of rotation of the head on the working plane is slanted in relation to the horizontal projection of the main axis of advance, with a slant that is preferably equal to 45.degree..