Toolholder device for machine tools

A tool holder device for a machine tool having a drive spindle for imparting rotation to a cutting tool, comprising:

• a) a holder body to be coaxially coupled to the drive spindle for joint rotation therewith;
• b) a driven toolholder coupled to the holder body for coaxial rotation with the holder body and for axial movement relative to the holder body, said tool holder including means for coaxially holding the cutting tool;
• c) spring means disposed between the holder body and the driven toolholder for yielding axially to cause the toolholder to axially displace relative to the holder body only when an axial thrust force exceeding a set value is applied to the cutting tool;
• d) a set of first displacement detecting elements on the holder body at circumferentially spaced locations about an axis of the holder body and the toolholder;
• e) a set of second displacement detecting elements on the toolholder at circumferentially spaced locations about said axis and arranged interdigitatingly with said first displacement detecting elements with clearances therebetween;
• f) displacement translation means between the holder body and the toolholder and having sloping surface means for converting an axial displacement of the toolholder due to said axial thrust force exceeding the set value into a circumferential displacement of the toolholder, said sloping surface means being disposed in a region radially inward of said first and second displacement detecting elements such that said circumferential displacement of the tool holder in the region of said sloping surface means will cause an enlarged circumferential displacement of said second displacement detecting elements of the toolholder relative to the first displacement detecting elements of the holder body;
• and
• g) means for sensing said enlarged circumferential displacement to detect at least said axial thrust force exceeding the set value.