Oversized holes can be caused by inadequate workpiece support,worn guide bushings, worn or loose spindle bearings, or bent reamer shanks. When reamers gradually start cutting larger holes,it may be because of the work material galling or forming a builtup edge on reamer cutting surfaces (Figure H-128). Mild steel and some aluminum alloys are particularly troublesome in this area. Changing to a different coolant may help. Reamers with highly polished flutes,margins,and relief angles or reamers that have special surface treatment may also improve the cutting action.