A curtain assembly comprises a rotatable drive element wherein at least one helical guide structure is formed on, or into, the outer surface of the drive element. A drive attachment element having a structure that communicates with the helical guide structure to move the drive attachment element axially along the drive element when the drive element is rotated. Specific embodiments incorporate either a manual or motor-driven rotation assembly for rotating the drive element. Further specific embodiments involve a helical guide structure that comprises a helical groove and a structure that comprises a tooth that engages with the helical groove.

A two-way indexable V-shaped cutting insert having first and second rake surfaces located in a front insert surface thereof. First and second relief surfaces respectively connect the first and second rake surfaces to first and second converging insert abutment surfaces, respectively. A first cutting edge is located at an intersection of the first rake surface and the first relief surface. A second cutting edge is located at an intersection of the second rake surface and the second relief surface. A first relief angle is formed between the first relief surface and the first converging insert abutment surface. A second relief angle is formed between the second relief surface and the second converging insert abutment surface. The first and second relief angles are obtuse. In a cutting tool, the two-way indexable V-shaped cutting insert is releasably secured in a tool holder by means of a fastening member.

A cutting insert includes opposing insert first and second side surfaces. The insert first side surface includes a first mounting arrangement. The first mounting arrangement includes a) at least one first side abutment surface facing away from the insert second side surface, b) a first stopper abutment surface oriented transversely to the at least one first side abutment surface and c) two opposite-facing first wedge abutment surfaces oriented transversely to the at least one first side abutment surface and converging forwardly. An insert holder has a corresponding pocket mounting arrangement for engagement with the first mounting arrangement.

A constant rake planar cutting edge fluted drill bit and a method of manufacturing the same. The drill bit includes a planar cutting face formed at the tip end of the bit by a motion of a rotating machining wheel respective to a stationary blank in a first step. Once the cutting face is formed, the blank is rotated and translated in a direction parallel to an elongated axis, during which the rotating machining wheel creates a flute. Upon completion of the first flute, the bit is rotated accordingly and the processes are repeated to create each subsequent planar cutting face and respective flute. The process can also be completed in a slightly modified version of a reverse process, fabricating a flute prior to formation of the planar cutting face of the bit.