The following article is on Tree Harvesters, essentially they use a much larger Chainsaw and the Chainsaw Chain and bar is a lot longer. One of the issues with these machiens is that they go through a lot of chainsaw chains. Companies using tree harvesters have to have a large supply of sharpend chainsaw chain on hand in order for their harvesters to function at their full capacity.
When you put a tractor and a chainsaw together you get what you could call the ultimate chainsaw a tree harvester. Developed in Sweden and Finland the first single grip harvester head came out in the early eighties. Their use these days is wide spread through out Canada and the US.
A tree harvester head can be fitted to a large tractor type carrier with rubber tires or tracks like an excavator or hydraulic log loader. The head in the upright position opens up like a pair of arms. The lower arms have spiked drive wheals on each side and a large chainsaw bar and chain mounted below. The upper arms or delimbing knives are slightly curved to go around the tree and sharp around the top edge. The head is pinned inside a U shaped hanger which allows it to be placed in an upright position or swing down to a horizontal position.
For tree falling a small hydraulic piston pushes the head up into an upright position. The operator swings the head against a tree and closes the grab arms. The operator will usually grab the tree a little high then operate the drive wheals to lower the cutting point of the head as close to the ground as possible with out damaging the cutting chain. When he is ready to cut the tree a slight lifting pressure is applied and the saw is operated. A small movement tells him the tree is cut off the stump. He then swings the tree off the stump. The direction of fall is opposite of this and is how the falling direction is controlled. As the tree falls the head swings down with it into the horizontal position.
With the tree on the ground and firmly held in the harvester head the operator is now ready to process the tree. The operator usually will have a small computer screen telling him the diameter of the tree measured by the head in this case at the butt. He can run the head up the tree by operating the drive wheals and the computer will measure the length as it travels up the tree and measure the top size at a desired length. As the head travels up the tree trunk the delimbing arms will cut all the limbs off.
When processing you will be trying to get the most value out of a log by getting the most preferred lengths possible for your buyer. The operator will be fully trained in spotting defects or rot, things that could devalue a log. He will usually program presets into the computer of these preferred lengths and corresponding diameters so once he identifies the species its just a matter of pushing the correct preset and the log is automatically fed through the head at approximately 17 ft per second taking all the limbs off at the same time and automatically stopping at the correct length. After a quick check to see if the top diameter is correct, the saw is operated and he is off to the next tree.