tool cassettes in a progressive forging machine are configured to facilitate their machine controlled changeover by the ability to be installed and removed through vertical movement in and out of the machine and by the incorporation of self - alignment features . the die cassettes , which have precision machined cylindrical surfaces , establish the work station centers of the machine on the die breast and receiving zones on the slide for the punch holder cassettes are established with gage blocks that are sized by reference to the respective die work station centers . the cassette system can provide a level of alignment between punch and die elements not previously practical in large machines and a flexibility in tool size that is not subject to the traditional restraint of work station center - to - center distance .