Split-jaw lathe chuck with lockable inner jaw parts

A lathe chuck comprising:

• a chuck body rotatable about an axis and formed with a plurality of angularly spaced and radially extending inner guides and with a plurality of angularly spaced and radially extending outer guides, each of said inner guides in turn having a respective axially forwardly directed and radially extending blocking surface and a respective axially forwardly opening recess at the respective blocking surface;
• respective inner jaw parts radially displaceable in said chuck body in said inner guides;
• means including at least one operating element engageable with said inner jaw parts for radially displacing same in said chuck body in the respective inner guides between radially inner and radially outer positions;
• respective outer jaw parts projecting axially from said chuck body and radially displaceable therein in said outer guides;
• respective coupling members carried in said inner jaw parts and engageable with the respective outer jaw parts and each engageable in a predetermined radial position of the respective inner jaw part in the respective recess, said members when not engaged in the respective recesses riding on the respective blocking surfaces and being in a coupling position engaging both of the respective parts and coupling same together for joint radial displacement and being axially displaceable only when aligned axially with the respective recesses from said coupling position into a decoupling position engaged at least partially in the respective recesses for relative displacement of the respective jaw parts;
• and
• safety means for displacing said members between the coupling and decoupling positions only when said members are aligned with the respective recesses in said predetermined radial positions of the respective inner jaw parts, said safety means including respective cam locking elements carried in said inner jaw parts, engaging the respective coupling members, and displaceable between end positions corresponding to the coupling and decoupling positions of the respective coupling members, said members and elements being jointly radially displaceable with the respective inner jaw parts.