Circular-saw dlfachines may be considered in accordance with their construction rather than with reference to their uses or size. The methods of holding and driving the saw-discs are many. The saw may be (t) upon a fixed arbor, the stock or work being fed by hand along a guide; (2) upon a fixed arbor, the stock being fed upon a carriage; (3) upon a movable arbor swung in a frame, the saw being brought down upon and thrust through the work; or (4) upon a movable arbor mounted in a sliding carriage, the saw being fed through the stock. The disc may be set (r) at exactly right angles to the arbor; (2) a trifle out of square, so that it will cut a groove wider than the extreme distances between teeth sides; or (3) very "stag gering," so that it will cut a "gain " or groove.
Machines with mandrels having only a rotary motion may be divided into those (1) in which the table has no motion nor adjustment, (2) in which the table tilts in a plane at an angle to the saw-arbor, and (3) in which the table or carriage slides. The saw-arbor is either fixed or movable, and may receive its rotation from hand-, foot-, or horse-power, or it may be belt-driven or " direct-driven " by a high-speed engine.
Machines in which the mandrel moves in effecting the cut may be divided into those (i) in which the arbor is in a sliding frame and (2) in which the material is in a swinging frame. If arranged in gangs, circu lar saws may be (i) very close together, 'and may be used as rippers to make a great number of thin pieces, as laths; (2) quite far apart, used to bring boards or timbers to a given width; or (3) a considerable distance apart, used as cross-cuts to bring to a fixed and uniform length pieces passed between them. Two parallel circular saws may be so arranged in connection with two cross-cutters as to form a "square tenon" (ftl.
4), or one circular may work so as to form a round tenon upon the end of a rotated slat.
Gang —In ordinary use a gang ripping-machine (ftl.
r, fig. 8) has upon the arbor at the same time but two saws, one fixed, the other movable, with an adjustable guide-bar; but these two saws may be made the equivalent of three by governing the loose or movable saw with one lever and the guide with another, each having an index which gives accurate measure. In an improved self-feed gang rip-saw of the three disc type, the operator with one lever manages the movable gauge upon one side, and with another lever controls the position of the shifting saw; so that he can rip stock either of one width or of different widths.
Double and " " Ciro( lar ills consist of two or three saws, respectively, one above the other, with parallel axes; but when three discs are employed it becomes necessary to have a fourth, with a vertical arbor, to divide the board for the passage of the mandrel of the middle one. Double circular mills may be constructed with the top saw either mounted in one frame with the under one or carried by an inverted hanger separate from the lower frame; the latter being a very good way to make a double mill out of a single one. In this case the upper saw should have its arbor and girt raised and lowered by screws. The top saw of double mills should be run in the direction opposite to the bottom saw—that is, the tops of the two saws should run in opposite directions—thus making both the upper edge of the lower saw and the lower edge of the upper saw run toward the advancing log. This arrangement brings the cut of both the upper and the lower disc against the grain of the timber, making- the saws work more easily and track better, and dulling them less in sandy bark. By hanging the top arbor in advance of the lower there is avoided all danger of a wide board wedging between the standard and the saw. In improved double mills both ends of the upper arbor-hanger are raised and lowered together, and are thus kept parallel with the lower ones. Not only can the double mill saw larger logs than the single mill, but it can also use smaller and thinner saws, which can be run more rapidly and will cut a narrower kerf. These saws are more easily kept in order, are less liable to accident, and cost less to replace. When the lower saw is worn too small, it can be put on the upper. arbor. Double mills enable the sawyer to use saws of the right size, and thus to make as few slabs as possible, and therefore they are the best unless all the logs run small. In recent three-high cir cular mills the arbors are of such length that a 50-inch plank may fall away from the cut without touching the mill-frame uprights, and thus largely prevent accident to the saws and save the manual labor which would otherwise be necessary to lower wide planks upon the rolls or skids.