Abstract: A shaft adapter for removably mounting to the output or drive shaft of a grinding machine is disclosed. The shaft adapter is a three-component device which includes a collar portion, a compressible drive sleeve and an extension member. The extension member has a free-end adapted to matingly engage with a particular grinding cup. When the shaft adapted is mounted on the drive shaft, the compressible drive sleeve is compressed and elastically deformed between the corresponding, engaging ends of the collar portion and extension member so as to create a secure driving force between the rotating drive shaft of the grinding machine and the shaft adapter so that they rotate together as a unit when the grinding machine is in use.