1902 Encyclopedia > Saws


SAWS. Blades of steel with serrated edges have been used from time immemorial to rend or divide substances of various kinds, including metals and stone ; but the principal modern use of the saw is to divide wood. Modern saws are of the finest steel, but the ancients used bronze saws, and among uncivilized nations saws have been made with flakes of flint imbedded in a wooden blade, and held in place by means of bitumen (see Grimshaw, History, dec, of Saios), while obsidian has been used by the Mexicans, and shark's teeth and even notched shells form the saws of certain savage islanders. The pyramid-builders in Egypt cut granite and other hard stones by means of bronze saws set with jewels (see vol. xx. p. 124).

Space would fail to describe minutely the various adaptations of the saw to mechanical uses. It is indispensable to the carpenter, the furniture-manufacturer, the watch-maker, and manipulator of metals. It is one of the most trustworthy tools of the surgeon's case, while without it the dentist would of necessity drop back to the barbarous customs of a past century. Iron, horn, pearl, india-rubber, and the thousand and one conveniences of civilized life are dependent upon this useful instrument, which is but an exaggeration after all of the sharpest of knives, whose edge when examined under the microscope exhibits an array of saw teeth so minute as to present a smooth plane to the unassisted eye. As the chief use of the tool is to saw wood, the enormous timber industry of America has given an impetus to the improvement of the saw and its manufacture, which has no parallel elsewhere.

Saws may be classified as (1) straight (reciprocating in action), having a flat blade and straight edge, making a plane cut, or (2) circular or disk-like, cutting at right angles to the motion, or (3) cylindrical or barrel-shaped, with a convex edge cutting parallel to its axis, or (4) band-saws, being a continuous ribbon or band running upon an upper and lower pulley, making a plane or curved cut, with a straight edge parallel to the axis of motion. The oldest and commonest, with the widest range of adaptability, is the straight saw, with reciprocating rectilinear blade. In this class is included the ordinary hand-saw with its varying range of uses from fine to coarse and from rip to cross-cut, and with teeth of forms as various as are the different duties which it is calculated to perform. The teeth are long or short, cutting one way or both ways according to the " pitch or " set " which may be given, and which should be adapted to both the kind and character of the timber to be sawn. The " pitch " of a saw-tooth is the angle of the point with reference to the blade, and is found by sub-tracting the back angle from the front, 60° being the generic angle of saw-teeth, which, however, may be variously placed. From the smallest hand-saw to the largest " mill-saw' the same general rules apply. In the largest saws of this class may be named the "pit-saw," used in the earliest manufactures of lumber or timber, and worked by one person standing over the log and drawing upward while another in the pit below follows with the downward or cutting thrust. From the pit-saw we advance to the " gate-saw " used in the earlier adaptation of motive power to the cutting of timber, thence to the " muley-saw," suspended without strair. upon a pitman beneath, having its upper end hung in slides pendent from a heavy beam above. These saws must of necessity be thick, to sustain the heavy thrusts which they are expected to endure, and are consequently of '' heavy gauge," this being based upon the different sizes of wire, the largest gauge representing the thinner blade ; e.g., a, 4-gauge saw is much thicker than an 8-gauge, &c. From the necessity for more rapid production grew the '' gang-saw," a modification of the gate, differing from it only in length and thickness (less than one-third the thickness of the ordinary gate-saw and but about two-thirds its length). A large number of these, varying from 2 to 40, are strained in a gate or frame, at such distances apart as the thickness of lumber demands, and the log is wholly made into boards in one operation. Of the recipro-cating class of saws is the " cross-cut," used for cutting across the grain of the timber or wood to be converted into shorter lengths. The length, breadth, "pitch," and "set" of saws vary according to the use which is to be made of them and the kind of timber which is to be manipulated. In a cross-cut saw the cutting edge strikes the fibre at right angles to its length, and while its pitch is but slight (if any) it must sever from each side before dislodging the sawdust. "A slitting or ripping saw has the cutting edge about at a right angle to the fibre of the wood, severing it in one piece, —the throat of the tooth wedging out the piece." In slitting saws the "rake" is all in front, in the cross-cut on the side.

The circular saw is of comparatively recent origin, its introduc-tion dating from 1790, when Brunel first announced the principle. At first only circular saws of small diameter were used ; but, from the small "buzz-saw" of the watchmaker and fine metal worker, or the ripping saw of the planing-mill or carpenter shop, where small diameters have to be divided, the circular saw has passed to the saw-mill, where, in diameters of from 12 to 30 inches, it is the needful instrument for edging or ripping the lumber which drops from the log in an imperfect condition, requiring finer manipulation to prepare it for market; or in diameters of from 40 to 84 inches it may be found as the main saw of the mill for rending the logs as they come from the forest into shapes and sizes adapted for the various purposes of the builder. It is capable of dividing logs into boards one inch thick or upwards at as high a rate as 60,000 superficial feet in a day of twelve hours, while a straight (muley or gate) saw would give only 5000 to 8000 feet. In the chief lumber sections of the United States saws of 60 inches diameter are in most common use ; upon the Pacific coast saws of 8 feet diameter are not unknown. Attempts to work large circular saws in nests or gangs have not hitherto proved successful, but three, four, or five saws of 30 inches diameter hung on a single shaft or " arbor" may be used to trim and divide the boards or planks thrown off from a log.

Barrel saws, for the manufacture of staves for barrels, pails, or tubs, are in the form of a straight-sided barrel with both heads removed, and the stave ends of one head serrated.

For the manufacture of veneers, where valuable timber is to be economically manipulated, we have the segment-saw, constructed by bolting segments of saw-blades upon the outer rim of a cast-iron centre, forming a circular saw of the desired diameter, but with a cutting edge of so light a gauge as to waste but little of the valuable timber to be sawed, the cast-iron centre insuring the requisite stiffness and strength. With these saws veneers scarcely thicker than a sheet of paper may be cut, the width being accord-ing to the size of the log; such saws are often from 80 to 100 inches in diameter.

Circular saws of the larger size are often constructed with "inserted" teeth. A disk of steel of suitable size, having slots cut in its periphery of the exact size and shape of the tooth which is to be inserted, may have these teeth removed as often as the wear upon them may require, without reducing the diameter of the plate. The teeth of lumber saws have to be sharpened with the file at least three or four times in twelve hours' work, and a saw of five feet in diameter is rapidly reduced in size with a great loss of efficiency. In the insert tooth plate new teeth cost only about three cents (lid.) each, and the saw plate remains of its original diameter. Inserted teeth are of various forms and shapes, from that of the ordinary saw tooth, held in place by a rivet at the root of the tooth, to a " chisel point" held by an ingenious system of wedging.

Band-saws have for many years been used for continuous and rapid cutting in the planing mill or other wood-working estab-lishment, where scrolls or fancy lines and curves were to be followed, requiring great flexibility of the saw-blade. Of late, and notably within the past two years (1884-85), successful endeavours have been made to adapt them to lumber manufacture. The band-saw is a continuous blade or ribbon running over pulleys above and below, forming a "steel belt" whose serrated edge is always "in the cut." These saws are usually from a half inch in width (for shop work) to six and eight inches wide for the heavier work of the saw-mill, and in the latter have a cutting capacity of from 30,000 to 40,000 superficial feet in twelve hours. They are extremely thin (usually 16-gauge), and the kerf produced is so much less than that of the upright or the circular that a saving of at least 20 per cent, of timber is claimed in their use.

Saws used by surgeons, butchers, and in all branches of manufacture are but modifications of one of the varieties above described, and do not demand more extended description.

Saw-mills. Saw-Mills are factories for the conversion of forest trees into lumber and timber. The earliest form of saw-mill was unquestionably the saw-pit, still found in a modified form in shipbuilders' yards, the log being raised on trestle horses instead of one of the sawyers being sunk in the pit. Saws were run by windmill-power as early as the 13th century; and the use of water-power soon followed. The primitive water saw-mill consisted of a wooden pitman attached to the shaft of the water-wheel, the log to be sawed being placed on rollers sustained by a framework over the wheel, and being fed forward on the rollers by means of levers worked by hand. Good authorities mention saw-mills running by water-power in Germany as early as 1322. In 1663 an attempt to establish a mill in England was abandoned owing to the opposition of the sawyers, and no further attempt was made till 1768, when a mill was erected at Limehouse, but was soon destroyed by a mob. North America, with its vast forests, may be aptly termed the home of saw-mills. As early as 1634 a saw-mill was erected at the falls of the Piscataqua, near the line divid-ing Maine from New Hampshire. This was no doubt the pioneer of the vast array of mills which subsequently made Maine famous as a lumber-producing State for many years. From about the same date several mills were erected along the Atlantic coast of America, a description of one being that of all. In these mills the saw was attached by a long pitman from the wheel shaft to a ponderous gate, running in wooden slides upon two heavy posts, crossed above by a beam connecting the two sides of the mill-frame. The mill-carriage on which the log lay was pushed towards the saw by a rack and pinion, &c, moved by a feed-wheel. The daily capacity of these mills was from 500 to 1500 superficial feet. The first great improvement upon this class of mills was in the introduction of two or more saws to the gate, the general character of the methods remaining the same. With the demand for more rapid production came improvements in the "gang" feature, and the wonder of the age was the "Yankee gang," so arranged, by placing half the saws facing in one direction and the other half in the opposite, that two logs were worked up in one movement of the carriage, or, as in the " slabbing " gang, the outsides or slabs were cut from one log, which was then turned upon its flattened sides to the other set of saws which cut it into boards. The "stock" gang, "pony" gang, "slab-bing" gang, and "Yankee" gang are favourites with saw-mill proprietors, because of the uniform character of the lumber produced, and the saving of timber realized from the use of saws of scarcely one-third the thickness of the gate, muley, or circular.

Gang-saws are seldom thicker than 14-gauge, and are successfully worked at 18-gauge, making a saw-kerf or waste of but | inch, whereas the ordinary gate, muley, or circular takes ^ inch. The muley was introduced later than the gang, and was received with great favour, entering into more general use because of its comparative cheapness and adaptability where the sawyer had not to deal with large quantities of lumber. The muley mill dispensed with the ponderous gate and heavy posts of the saw-frame. While the lower portion of the mill is arranged much as in the use of the gate-saw, with the addition of necessary slides, the upper end of the saw is guided in a strong iron frame pendent from the weigh-beam overhead. On each side of this frame are slides in which are placed boxes, attached by a noddle pin and strap to the upper end of the , saw, keeping the tool in line with the cut, and the cutting is accomplished wholly by the downward thrust, the motion of the crank beneath imparting a forward motion to the blade in its cutting functions and a retreating motion as it rises from the cut. By an ingenious arrangement of the slides an increased oscillation may be imparted, the object being to cause the saw-teeth to hug the timber closer on the downward or cutting thrust, and to recede and run clear of the timber on the upward motion, thus decreasing the friction. Muley-saws are usually run at a speed of 300 revolutions of the driving wheel per minute, and the daily capacity may be stated at about 5000 superficial feet.
Water-power was used almost exclusively in saw-mills until 1835, after which year steam was rapidly substituted, until at the present time it is as difficult to find a water-power saw-mill as it is to find a gate or muley.

The use of the circular as the main saw of a mill is of compara-tively recent origin, the experimental point in its introduction having been passed only about the year 1855. Since that time it has rapidly reached the highest efficiency. Driven by engines of from 25 to 100 horse-power the circular saw-mill, under proper management, turns out from 20,000 feet per day for smaller to 50,000 and 60,000 feet per day for larger mills, in addition to running the double-edgers and trimming saws, requisite for trimming off the rough edges and bad ends of the lumber produced.

The modern saw-mill stands upon the banks of a river or pond, at an elevation usually of twelve feet from the level of the land to the saw-floor. The logs are floated from the forest (often many hundred miles distant from the mill) down the river, in lengths as desired. Piling driven at convenient distances in the water serves to hold the long pieces of timber, which, secured to the piles by heavy chains, form a strong "boom," floating into which the logs are penned or " boomed " until required. From the rear end of the mill, at the second story or saw-floor, a "jack ladder " is constructed of heavy timber, the lower ends resting in the bottom of the stream upon a bed of timber heavily weighted. Upon the sides of the jack ladder are laid ribbons of iron forming a track for the log ear, which, strongly constructed and with its top cross sections or "bunks" heavily studded with ^-headed bolts, is run under the water at a depth to allow the log to float over it in such manner that, as the chain running to the "bull-wheel" in the mill is wound up, the spikes of tiis car catch upon the under-side of the log or logs, which thus load themselves and are hauled up the incline to tho mill floor. Here they are rolled upon skids leading to the saw-carriage, and are soon running rapidly their course of manufacture. Loaded upon the " head-blocks, by a quick motion of a lever upon the standard, the "setter" inserts an iron "dog," which holds the log firmly in place ready for advancing to the saw. This is accomplished by one of several methods:—(1) by rack and pinion worked by "cone feed," in which a belt is moved upon two parallel cones to impart a more rapid or a slower motion to the pinion shaft; (2) by "rope feed," a rope, usually of wire, being attached to each end of the mill carriage, and passing over pulleys in the floor to a drum beneath, so arranged as to be under control of the sawyer in its feeding movement or in reversal to '' gig "the carriage back to its first position ; or (3) by "steam feed." This is the more modern and rapid means employed, and is sometimes termed " lightning feed." A steam cylinder of 8 or 10 inches diameter is laid upon the floor of the mill beneath the saw-carriage, its piston connecting with the carriage. Steam being admitted to the driving end of the cylinder (the length of which is according to the length of timber to be sawed, sections being added or removed at pleasure) the saw carriage is driven with lightning speed, both in the cutting feed and reversing "gig." Thirty ordinary cuts per minute, on 12 inches feed to the revolution of the saw, may be attained with this adaptation. As the limit of capacity for work with a circular saw is practically the ability of the operators to remove the lumber, 60,000 to 70,000 feet per day is no unusual cut, while a rate of 100,000 feet per day has been maintained (for a short period) by a single circular. The lumber as it drops from the saw falls upon " live rolls," a series of iron or wooden rollers connected by chain belts, which carry it within reach of the "edger," who rapidly passes that portion which requires " edging " or splitting through the " double-edger," to a carriage or truck on which it is pushed to the piling ground, or, in some mills, to another series of live rolls which take it to the front of the '' trimmer," an ingenious arrangement of table, beneath which are several saws which advance or recede at the operator's pleasure, cutting the lumber to even and uniform lengths, or trimming off such defects as may exist in the end of the piece. Ordinary lengths are 12, 14, 16, and 18 feet, and by use of the trimmer all superfluous ends are removed, leaving each piece of uniform length with its fellows. The waste of the log, consisting of the " slabs" and edgings, are carefully gone over, and such as are suitable for that purpose go to the '' lath " machines, where they are cut into strips four feet in length, § inch thick, and 1J inches wide, for lath and plaster work. In the sawing of logs, imperfec-tions are often discovered iu the timber, unfitting it for ordinary uses, and in many mills it is customary to saw such timber into "cants" of usually six inches thickness. These cants are turned over to a "butting saw," where they are cut into lengths of 16 inches (in some localities 18 inches) and turned over to the shingle mill to be manufactured into shingles. Shingles are tapering pieces f inch thick at one end, and TV inch at the other, and are used as a roof covering in lieu of slating or tiles. They are laid in uniform courses, with 4J to 5 inches of the butt end laid to the weather, and are good for from 20 to 30 years' wear upon a roof. An adjunct to the circular saw is often found in a top or upper saw, overhanging the main circular a little in advance of its track, for the purpose of enabling larger logs to be handled than the diameter of an ordinary circular will permit. The upper saw cuts into the top of the log in a line with the cut of the lower or main saw, thus increasing the depth of the cut. In California, where logs of 8 and 10 feet diameter are not unusual (larger logs being quartered by the use of gunpowder or other explosive, timber as much as 20 and even 25 feet in diameter being found in the redwood forests), an ingenious arrangement of four saws placed one higher than the other, some horizontal and others vertical, permits the handling of huge trees which until recently were not considered available. A thoroughly modern saw-mill embraces all which has been said regarding the circular, with the addition of the "gang" feature, for, while a majority of the saw-mills of North America are single " circulars," many of them have a rotary upon each side of the mill floor, the log-jack being in the centre of the building rolling its logs either to the right hand or the left. The larger mills have in addition to the rotaries from one to four gangs. In these cases the log usually goes first to the circular, where the slabs of two sides are removed, leaving a flat cant, which is then transferred to the gangs. These mills are fully equipped with all the modern patent improvements. The logs are drawn from the water by an endless chain running in a V-shaped log slide, the chains being provided either with spikes or concave chairs which hold the log from slipping back. One log follows the other in endless succession. On its arrival at the log deck on the mill floor, the manipulation of a lever causes an arm or arms to rise through the floor against the side of the log, which is partially raised and thrown with considerable force upon the skids leading to the saw carriage. When one log has been sawed, another is loaded by the simple touch of a lever in the hands of the sawyer, causing arms to rise in the skids under the log, which is thrown upon the carriage ready for the saw. When the first slab has been removed, the sawyer's touch of a lever brings through the floor the " nigger," a piece of strong timber, iron-bound and with sharp teeth or spikes protruding from its front face. Its motion tends slightly forward as it advances to a height of five or six feet above the floor, its spiked surface catching the side or face of the log, turning it instantly to any desired position. If the log is simply to be "canted" for the gang the two opposite sides or slabs are removed, and as the last cut is complete a hook thrown over the rear end of the cant prevents its return with the saw carriage and it drops upon rolls which move it so far out of the way of the returning carriage with its fresh load as is necessary to start it in an opposite direction to the gang which is to complete its manu-facture. Until now, and until it shall emerge from the gang, no hand of man has necessarily touched the log. Machinery guided by human intelligence has done all the work. When the log reached the carriage it was dogged, not with the old-fashioned lever dog driven by a mallet, but by the simple movement of a lever. It was brought to its proper position before the saw by nicely adjusted set works, which graduated its position to one-eighth of an inch. After the slab was removed, if another cut was required the same set works moved it forward with lightning quickness, leaving it at the exact point, to a nicety, requisite for the production of just the thickness desired lor the next piece. From the water to the pile in the millyard hands have necessarily been employed in actual handling of the product only at the edger and the trimmer, and in assorting the qualities upon the tram-car which removes it from the mill. Machinery, guided by human intelligence, has done all the heavy work. A mill answering closely to our description was recently burned at Bay City, Michigan, the yearly production of which for several years past has been 40,000,000 feet of lumber, besides shingles, lath, pickets, &c, cut from the slabs and waste. The total production of the saw-mills of the United States approximates 26,000,000,000 feet annually.

The "band" saw-mill is rapidly working its way into public favour because of the economy attending its use. The band saw is a long ribbon of steel, six to eight inches in width, running over large pulleys above and below, the upper pulley running almost vertically above the lower, the saw acting as a belt between the two and as the driving power to the upper wheel. These saws are very thin and have a manufacturing capacity of from 30,000 to 40,000 feet per day, with the consumption of 25 to 40 per cent, less power than is required for the ordinary circular saw of the same daily capacity for work. The main advantage found in the use of the band-saw is in the saving of timber (20 per cent.). The set works do not differ from those of rotary mills, and either cone, rope, or steam feed may be used in connexion with it.

A useful adjunct to the many saw-mills, which produce more waste than can be consumed in raising the necessary steam, is the "slab-burner" or "hell," a large circular brick furnace often 50 feet in height by 25 feet internal diameter, erected conveniently near the saw-mill, into which by chain carriers leading to an opening at a sufficient height from the bottom, the sawdust, edgings, worthless slabs, and debris of the mill are conveyed, to be destroyed by fire.

Shingle Shingle Mills.—A standard shingle is four inches wide, and all Mills, computations of quantity are based upon that width, although the individual shingle may be six or eight inches wide or as much as 18 inches, in the latter case counting shingles. A shingle mill differs from a saw-mill in the adaptations of machinery. Saws of 16-gauge, 40 inches in diameter, are most commonly employed. In cases where shingle manufacture is carried on in connexion with the saw-mill, the process of preparing the blocks has already been described. A majority of the shingles manufactured, however, are made in mills built for the special purpose. Logs suitable, usually of a medium quality, are placed before a ''bolting" or 11 drag" saw, which severs them into the required length. The block is then stripped of its bark and sap by splitting off a section of the outer circumference to the heart wood, with axes; it is next quartered, and the inside section of heart, which is never sound, removed; and then it goes to the machine for manufacture. The machines are sometimes horizontal, sometimes vertical, but all work upon the same principle, viz., that of a tilting table, allowing a thick butt and a thin point to be alternately taken. The shingles as the}7 drop from the saw are rough-edged, and require to be "jointed," generally upon a rapidly revolving wheel, upon the face of which are secured four well-balanced knives, which, as the shingle is pressed against them, eat away the imperfect edge with great rapidity, leaving a straight smooth edge, which when laid upon a roof makes a good joint with its fellows. The edging or jointing process is often performed with small saws in place of the wheel-jointer. The shingles are usually packed in bunches con- taining the equivalent of one quarter thousand 4-inch pieces, and are more used for roof covering than any other material in the United States or Canada. (G. W. H.)

The above article was written by: G. W. Hotchkiss, Chicago.

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