Abstract: Disclosed is a lathe cutting tool assembly found of a tool holder which has a seat to accommondate a cutter insert, the cutter insert being provided with a clamping groove or bore. The insert is held in the tool holder by a clamping shoe. The clamping shoe is tightly secured to on the tool holder. To protect the clamping shoe and improve the seating of the cutter insert in the tool holder, a clamping plate is secured to the clamping shoe and lies upon the cutter insert. A projection is provided on the bottom of the clamping plate facing the cutter insert and is in clamping contact with the groove or bore. The tool assembly is especially adapted for a turning chisel.