machines usually employ circular saws, which are generally "flat" or on vertical arbors. Some have reciprocat ing carriages for the "spalt," and others have a rotary motion. Some employ but one saw; others, two or more. The logs are sawed into bolts or lengths required for shingles either by a drag-saw or by "bolters" hay ing two saws, which are set as far apart as the length of the required bolt. The shingle-machine (jig. i) divides the bolts into shingles, the block or bolt being placed on the tilt-table (A). The slides (.8) are so planed into the tilt-table top (A) as to allow them to be moved ahead toward the saw as the latter wears up. This table hangs on trunnions and oscillates as the "tilt-lever" (C) is moved from side to side. The " butts" and '' points of the shingles are regulated by the four hand-wheels (D), which are also used to set the table-top parallel with the track of the machine. The tilt-levers do not have to be moved every time a shingle is cut, but are used to throw knots, etc., when possible, into the point of the shingle, and also so as not to saw the wrong way of the grain. The spring-lock on the tilt-lever (I) is for holding the lever against the stop, so that it will not rebound. When "heading" is being cut, the stops are turned down, so as to hold the table level. As heading is the same thickness from one end to the other and does not require a tilt-frame shingle-machine, the shingles go to the "jointer," who joints them on the edges (usually on a wheel car rying knives), throwing aside the knotty ones to be slit up later on a knot saw.
In one variety of flat-saw shingling-machines the ways on which the shingle-block rests can be adjusted to any thickness or any taper by four hand-screws. The first screw changes the shingle to thick or thin, the second regulates the butt, the third controls the top and is held by jam nuts, and the fourth changes the rake in the saw on the top. On such a machine, if a block is 4 inches thick on one end and io inches on the other end, it can be sawed with all the butts on one end and all the tops on the other, thus bringing the block even at each end and making the entire block into shingles, except a thin slab. The saw strikes the block on the side, which operation is considered to make a smoother shingle than by entering the saw at the end.
A new type of shingle-dresser is a planer with an endless wooden car riage having beds, in which the sawed-joint shingles arc put and held in place by pressure-rolls held down by springs, so that while being planed they are sprung into a dished board transversely across the shingle-bed. When they come out, each has a convex upper face thinned down at the left edge, so that, in driving, the thick side overlaps the thin edge, and thus the shingles, when on the roof, rest on their two edges, leaving an air-space between. It is claimed for them that as soon as the rain is over they dry at once, while joint shingles, lying flat together, become waterlogged and rot in the lap. A 24-inch shingle of this kind is put z r inches to the weather, while in a joint it would be only 7Y, inches, thus covering more surface, saving one-third in lath, and making, it is claimed, a roof that will last much longer.
The or which is an example of a continuous-acting mulay or jig, is practically a pair of driving-pulleys with a steel belt, one edge of which has cutting-teeth. It may be considered a development of the endless knife used in cutting cloth, the microscopically fine teeth of the band-knife being magnified in the band-saw just as the cold-sawing disc for cutting iron merges into the toothed circular saw for the same purpose. In band-saw machines there can be but little variety except that which is purely structural. In every form there must be a driving-wheel and a driven wheel, the saw-blade being the belt. Provision must be made for a constant yet adjustable band-tension, and there must also be a coarse adjustment for taking up the blade as it is shortened by breakage and mend ing,. In all there must be either (r) a carriage permitting the stock to be fed in one direction without swerving, or (2) a table upon which the mate rial may be either fed against a guide or moved in the horizontal plane, to permit of cutting curves built up of very short straight lines. All require for the blade sonic guide to keep it from running out of line; all demand that the wheels shall have a friction surface that will lose as little as pos sible by slip caused by the very unfavorable material constituting the belt; all should have provision for suddenly stopping the driving-wheel. Sonic have an arrangement by which the tire of the driven wheel may slip around upon its felloc, so that when the driving-wheel is suddenly braked the driven wheel may keep on revolving, but the blade may stop.
Band-saws are used to cut both straight and curved lines, and are employed on the most delicate fret-work and also on the heaviest log ser vice. They are either hand-fed or power-fed. The wheels of those for fret-work are from 30 to 72 inches in diameter; of those for logs, from 72 to 96 inches. The saws for fret-work are as narrow as of an inch; those for log-work, as wide as S inches. The great advantage of the band saw is the thin kerf it makes, which saves both lumber and power. As compared with an equally good circular saw, a good band-saw will save a fifth of the material in working a choice lot of logs. Moreover, the lum ber produced by the band-saw is better and smoother and can be dressed with less waste than that turned out by the circular saw. As the band saw makes its cut at right angles to the grain, it has an advantage over the circular saw, which cuts largely parallel with the grain. The smaller the disc, the greater its disadvantage; furthermore, a circular saw is liable to scour the log with its rear edge, thereby reducing the quality of the lumber. For places where it would be difficult to put a band-saw with the ordinary large frame, and for a class of work where a large saw is not needed, as in ordinary pattern-work, there is provided a machine (fl. 12, fig. 7) which can be attached to any ordinary post or wall-plate.