Indicating of unsharp teeth at a disc saw by measuring of speed of rotation

A method for indication of sharpness of teeth at a harvesting head at a forestry machine during operation in a forestry stand with essentially uniform properties of its trees, which harvesting head comprises a cutting arrangement of a type that comprises a disc that rotates at a variable speed and that is provided with teeth, and an accumulation compartment for accumulation of cut trees, the method comprising the steps:

• a) initiating an accumulation sequence with a highest permissible and a lowest permissible speed of rotation of the disc, and an accumulation compartment capacity value being stored in a memory at a processing unit;
• b) increasing the speed of the disc until the highest permissible speed of rotation of the disc is registered;
• c) maneuvering and placing the working head against a tree, after which the tree is cut, wherein at each cutting, the disc is exposed to a resistance that leads to a reduction in the speed of the rotation of the disc, wherein the reduction of speed of rotation increases as the teeth become more blunt;
• d) registering a reduction of the speed of rotation of the disc during the cutting and subtracting the reduction of the speed of rotation of the disc during the cutting from the speed in b),
• e) filling the accumulation compartment by repeating the steps c) to d);
• and
• f) in accordance with a determination that the speed of rotation of the disc reaches the lowest permissible speed before the accumulation compartment has reached the accumulation compartment capacity value, transmitting, to a driver, a signal indicating that the teeth of the disc are too blunt.