Abstract: A tanning machine wherein a pressure roller urges one side of a hide or skin against the blades of an elongated rotary severing device has a grinding unit which treats the blades of the severing device and is mounted in the frame of the tanning machine. The grinding unit has elongated straight first guide members which are fixedly mounted in the frame and extend in parallelism with the axis of the severing device, a first carriage which is reciprocable along the first guide members by a motor through the medium of an endless chain and carries second guide members extending radially of the severing device, a second carriage which is reciprocable along the second guide members and supports a grinding tool, and a cam and follower arrangement which moves the second carriage along the second guide members in response to reciprocation of the first carriage along the first guide members.