Universal grinding machines (Fig. 200) are used for grinding pieces which have been distorted by hardening, although it is sometimes profitable to finish soft pieces also by this method. This machine is similar to a lathe, with the exception that instead of a tool for removing the stock, a revolving wheel made of abrasive material is employed.

A surface grinder is a modification of the planer, but uses a revolving, abrasive wheel instead of a tool for removing stock from flat surfaces.