A wide variety of different forms of saws and similar cutting devices are generally known and used. Conventional manual saws, as used for cutting both wood and metal, have saw teeth inclined in one direction. In use, the saw moves reciprocally; movement in one direction constitutes a cutting stroke whereas movement in the opposite direction merely returns the saw blade to the beginning of another cutting stroke.
Saw teeth are often bent outwardly of the plane of the saw blade, alternately left and right, to produce a cut wider than the saw blade, so that the blade can slide through the cut easily without jamming. For carpentry and metal work, the saw usually has a single handle and is operated by one person; for felling trees larger two-handled saws are employed, worked by two people. In the latter, some of the teeth may be inclined in one direction and the balance inclined in the other so that a partial cutting action is achieved in each stroke of the saw.
Mechanically driven saws of various types operate on the same basic principles. Thus, the teeth of circular saws, including planing and smoothing saws, are usually all inclined in a single direction and the saw is consistently rotated in one direction. The same characteristics apply to chain saws, in which the saw teeth are mounted on an endless chain driven either by an electric motor or an internal combustion engine. For bench work, an endless band is often employed as the carrier of the saw teeth, with a unidirectional drive. It is also known to provide gang saws consisting of several parallel blades held in a single frame, with the blades actuated in a reciprocating movement to cut the material simultaneously in several locations. The variety of mechanically driven saws is almost endless, including saber saws, jig saws, and many other examples.
In any of these known saws and similar cutting devices, the saw teeth are subject to substantial wear. This is true even with respect to saws employed in cutting relatively soft woods, since the wood is at least somewhat abrasive and continuously erodes the saw teeth. In metal saws, harder metals are employed for the saw teeth, but the problem of wear is nevertheless present.
In virtually any conventional saw that is used regularly, the wear on the teeth necessitates periodic sharpening in order to maintain an efficient cutting operation. Saw sharpening requires specialized machinery and trained personnel; precision alignment and shaping of the teeth is essential to effective operation. Moreover, care must be exercised in grinding the saw teeth, in a sharpening operation, to avoid overheating of the teeth with consequent possible annealing and softening of the cutting elements of the saw.
One particular application in which the necessity for regular re-sharpening of a saw is highly disadvantageous is in the felling, cutting, and shaping of trees for railroad ties. This is particularly true in tropical and subtropical locations, where work conditions are quite difficult and skilled personnel are frequently unavailable. In applications of this kind, and especially where the trees are of hardwood varieties, the cost of saw maintenance may be an appreciable element of the overall cost of operation, and may be so high as to preclude economical use of available resources. Most conventional saws are inadequate and uneconomical, particularly for the cutting and shaping of tropical hardwoods, because the useful life of the saw is quite short and frequent re-sharpening and setting is necessary.
Another disadvantage of conventional saws is that the saw teeth have no point of support other than the actual cutting edges. This is particularly true with respect to planing saws, which often exhibit excessive vibration caused by the lack of support for the saw teeth, other than the cutting edges.
One saw construction in which these difficulties are partially alleviated is described in Topolinski U.S. Pat. No. 2,795,247, issued June 11, 1975. In the construction shown in the Topolinski patent, the saw teeth are inclined alternately in opposite directions, and alternate pairs of the saw teeth are bent outwardly of opposite sides of the saw blade. With this construction, the trailing teeth of each pair are partly self-sharpened as they ride through the cut made by the other teeth of the pair, and the saw can be reversed in direction to afford an extended period between re-sharpening operations. However, the use of the conventional laterally bent construction for the teeth to widen the saw cut limits the effectiveness of the self-sharpening operation and allows for undesirable vibration. Moreover, the individual teeth still have no support other than the actual cutting edge of the tooth itself.