Wear-resistant chuck for driving hard-shank bits

A chuck having:

• a base body for affixation to a drive spindle, said base body defining an axis of rotation;
• radially movable clamping jaws carrie din said base body, situated for engaging and clamping a shift of a bit,
• each said clamping jaws, or a clamping part affixed to a respective jaw having at least one clamping surface for engaging said shaft of a bit,
• means rotatably mounted on said base body for positioning said clamping jaws,
• wherein said clamping surfaces in said clamping jaws or clamping parts are directed exactly parallel to said axis of rotation and have a shape resulting, when engaging said shaft of a bit, in an essentially linear or stripleike contact with said shaft;
• and
• wherein said clamping jaws or said clamping parts affixed thereto, at last in the region of their clamping surfaces, are coated with a layer of grains of diamond dust, and the material of said clamping jaws or said clamping parts affixed thereto in said regions is softer than said diamond dust, to permit grains of said diamond dust to embed themselves and to bury themselves in said material, whereby, at least in said regions, said clamping surfaces have the property of greater resistance to abrasion than hardened steel.