Cable Backhoe

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Leo Heikkinen Collection

This is a photo from the collection. It is included among the loaders because Leo Heikkinen was the inventor of the knuckleboom log loader, and he is here operating a cable backhoe. You only need to look at this thing briefly to understand the overwhelming benefits that came forth with the addition of hydraulics to the backhoe. Indeed backhoes were almost unknown until hydraulics became commonly available, with excavation before that being done either with a 'shovel', a drag line, or a clam. Now, of course, hydraulic excavators are everywhere.

The notable thing about this machine is that it operated with just two cables which is helpful to the operator as it takes the coordinated use of a hand and a foot for each line. In typical operation, a hand lever is pulled to engage a friction to wind in the cable, and the cable is held with a foot brake. Given the geometry of the cables, the upper cable will lift the boom and/or extend the dipper (or arm). Since the arm can only extend (bending at the elbow) if the digging line pays out, if you held the brake on the digging line, and pulled the lifting line, the whole thing would come up. Slacking the digging line would cause the arm to extend and the boom to drop. This device clearing needed to swing to the left and right as well, but I have no clue how this was accomplished.

When loggers needed a boom to swing, they almost invariably used a winch to pull it one way, and a 'squirrel block' to return it. A 'Squirrel block' is just a weight hanging on a cable which runs through a block (pulley) above. When pulled under power with the cable, the squirrel block is pulled up the tree, and then when the power is released, the weight of the squirrel block pulls the line back. The weight of the squirrel block had to be commensurate with what was being pulled. In the logging world, a squirrel block is typically a chunk of a log, often a long butt.

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- - Updated 03/27/2008