Through-in grinding method and through-in grinding apparatus

In centerless grinding there are the in-feed and the through-feed scheme, each having their respective advantages and disadvantages. When a work being machined by centerless grinding has plural portions being machined, those portions can be distinguished as portions being machined suitable for in-feed and portions being machined suitable for through-feed. Then, the present invention, using the same centerless machine, performs through-feed grinding in the first half of the process, then automatically switches from that and performs in-feed grinding in the latter half of the process. Thus, in a single piece of work being machined, sites suited to through-feed grinding are subjected to through-feed grinding, and sites suited to in-feed grinding are subjected to in-feed grinding. Not only so, but it is unnecessary to alter the setup between the first half of the process and the latter half of the process, wherefore centerless grinding can be performed very efficiently.