Abstract: A method of calibrating and orienting forming rollers of an Assel-type rolling mill, and more particularly, of calibrating an Assel mill for rolling thin-walled tubes of pre-pierced hollow bodies about a mandrel, using at least three generally conical rollers that are circumferentially spaced about the mandrel. The orientation of each forming roller is adjusted so as to position the roller inclination relative to the mandrel axis of roll by an expansion angle .alpha. of approximately 7.degree. to 30.degree.. Each forming roller is also adjustably oriented so that its smoothing part relative to the mandrel axis of roll defines a transport angle .gamma. of approximately 7.degree. to 17.degree.. In further accordance with this invention, each forming roller is configured so as to have an opening angle .beta. of approximately 4.degree. to 15.degree..