Lockable drill chuck

A lockable drill chuck comprising:

• a chuck body rotatable about an axis;
• an adjustment body rotatable on the chuck body relative to the axis and formed with
• a rim engaging inwardly over the chuck body,
• an outer skirt projecting axially forward and formed with a radially inwardly open arm pocket and with a pair of radially inwardly open abutment pockets, and
• an inner collar projecting axially forward and forming with the outer skirt an forwardly open annular space, one of the bodies being formed with a plurality of angled guides spaced about the axis and the other body being formed with a screwthread;
• respective jaws in the guides having toothed edges meshing with the screwthread, whereby rotation of the adjustment body on the chuck body in a forward closing direction about the axis moves the jaws radially toward one another and opposite rotation in a reverse opening direction moves the jaws radially apart;
• an array of radially inwardly directed sawteeth on the adjustment body;
• a locking ring fixed on the chuck body having an elastically deformable locking arm received in the arm pocket, having
• a free outer end,
• sawteeth offset from the free end and engageable with the adjustment-body teeth, and
• an axially projecting actuation pin offset from the free end and at the sawteeth,
• the arm being radially deflectable between an outer meshed position with the locking-arm sawteeth meshing with the adjustment-body sawteeth and an inner out-of-mesh position;
• a positioning ring rotatable on the chuck body about the axis between angularly offset locked and unlocked positions and having
• an actuation part engageable in the locked position with the free end of the locking am to urge same radially outward into its outer position, the sawteeth being angled such that in the meshed position they positively inhibit rotation of the positioning ring relative to the locking ring in the opening direction while rotation of the positioning ring relative to the locking ring in the closing direction cams the sawteeth radially apart,
• a cam surface engageable with the actuation pin in the unlocked position to force the pin radially inward and set the arm in the out-of-mesh inner position,
• the arm being sufficiently elastically deformable that, in the locked and meshed positions, rotation of the locking ring in the closing direction relative to the locking ring cams the teeth apart enough to slip angularly relative to one another;
• and
• abutment tabs on the locking ring engaged in the abutment pockets limiting rotation of the positioning ring to movement between its positions.