a well casing scraping apparatus includes a generally cylindrical mandrel connected to a power driven rotatable work string or conduit . at least one peripheral ramp surface is formed on the mandrel and an annular scraping means is formed by the assembly of a plurality of externally toothed arcuate segments around the ramp surface portion of the tool support , with each segment having an internal arcuate ramp surface conforming to the adjacent portion of the mandrel ramp surface . retaining sleeves are provided for the tool segments which not only retain the segments against radial outward movement but confine the segments axially to engagement with a particular portion of the ramp surfaces , whereby the effective working diameter of the segmented scraping means may be effectively controlled by changing the axial position of the retaining sleeves .