1. Field of the Invention
The invention relates to the field of sharpening devices for chain saw cutters and particularly to a sharpening device that is mounted to the chain saw housing, and which when actuated will automatically sharpen the cutters when the cutters are in motion.
2. Description of Prior Art
There have been numerous designs for saw chain sharpeners mounted directly upon the chain saw to eliminate the tedious and time consuming hand filing of the chain cutters. Such chain saws use top sharpening chains of the type disclosed in U.S. Pat. No. 3,183,973, Chain Saw With Sharpening Means, by Muir.
A typical prior art sharpener is disclosed in U.S. Pat. No. 3,040,602, Saw Chain Sharpener And Method by R. R. Carlson. The Carlson sharpener includes a body pivotally mounted to the saw housing which contains an adjustable sharpening element mounted thereon. To sharpen the chain one need only rotate the body so that the sharpening element contacts the chain, preferably at a point where the cutters are traveling over the driving sprocket. While this design works it had several drawbacks. One of these is that the amount of force applied to the cutters is variable and thus there is always a possibility of over-sharpening and prematurely wearing the cutters. It is also subject to clogging due to debris becoming caught between the sharpening element and body.
Another example can be found in U.S. Pat. No. 3,495,795, Easily Dressed Sharpener by M. D. Tupper. In the Tupper design a carrier housing is movably mounted on the saw housing. A bushing is slideably mounted in the carrier. Rotatably mounted in the bushing is a shaft having a grinding stone at one end. The stone is biased away from the bushing by means of a spring. The operator pushes a knob attached to the opposite end of the shaft causing the stone to engage the cutters. The biasing means provides a resilient contact with the cutters tending to limit the force applied. Wear is compensated for by means of a separate screw which moves the carrier toward the cutters. This design is relatively expensive to manufacture, is subject to clogging, and there is no real means to totally control the force applied. Furthermore the screw has no detent means so it is difficult to know how much advancement should be made in order to compensate for wear.
A design which eliminates the clogging problem and provides for accurate adjustment of stone feed to compensate for wear was developed by J. L. Dilworth and is disclosed in U.S. Pat. No. 4,062,253, Chain Saw Sharpener. The Dilworth design includes a stone movable from a retracted position to one in engagement with the cutters. A spring within the housing is used to bias the stone to the retracted position. An adjustment knob is provided on the opposite end which when rotated feeds the stone to compensate for wear. An internal detent is also provided which provides accurate feed control. The movement of the grinding stone is controlled by an adjustable stop. Thus having the mechanism within the housing eliminates the possibility of clogging, and the use of the detent provides accurate feed. But even here there is a possibility of over-adjusting the stone, which can result in premature wearing out of the stone and a reduction in the life of the cutters.
Other patents of interest are U.S. Pat. Nos. 3,147,644, Sharpening Means For Chain Saws by J. W. Oreilli; 3,596,689, Saw Chain And Sharpeners by J. W. Oreilli; and 3,301,098, Chain Saw Sharpening Wheel by J. W. Oreilli.
It is therefore a primary object of this invention to provide a chain saw sharpener which automatically compensates for grinding stone wear.
Another object of this invention is to provide a chain saw sharpener that is inexpensive to manufacture.
A further object of this invention is to provide a chain saw sharpener that does not require precise positioning in order to accomplish sharpening of the chain.
A still further object of this invention is to provide a chain saw sharpener that is relatively insensitive to the force applied by the operator, thus reducing the possibility of prematurely wearing out the chain.