A method is described for centring semi-finished parts (2) which are to undergo mechanical machining, comprising the steps of preparing a centring device (1) comprising three centring elements (11) spaced apart angularly at a regular pitch, capable of coming into contact with the semi-finished part (2) to move it into a centred position, each of the centring elements (11) being movable along a preset radial direction (Y), the radial directions intersecting at the geometrical axis (X) of centring of the part. The method further makes provision for the steps of moving each centring element (11) along the corresponding radial direction (Y), with controlled and independent movement of each centring unit relative to the others, by means of a respective drive means (15) associated with respective means of transmitting the motion (16, 17) capable of converting the rotational motion of each drive means (15) into translational motion of the corresponding centring element (11), and of adjusting the position of each centring unit (11) as a function of the torque developed by the respective drive means (15), until a condition of centring is reached in which all the torque forces developed by the drive means of the corresponding centring elements are greater than or equal to a preset threshold value indicating that the desired centring position of the part (2) relative to the geometrical axis (X) of the centring device has been reached. A centring device operating according to the above-mentioned method is also described. |