Kitabı oku: «Handwork in Wood», sayfa 2
As forests are cut away along the water courses, railways have to be resorted to more and more, Fig. 28. This has had a stimulative effect on the logging business, for now the logger is independent of the snow. On account of the steep grades and sharp curves often necessary in logging railways, a geared locomotive is sometimes used, Fig. 29. It can haul a train of twenty loaded cars up a twelve per cent grade. The geared engine has also been used as a substitute for cable power, in "yarding" operations. The "turns" of logs are drawn over the ground between the rails, being fastened to the rear of the engine by hook and cable. This has proved to be a very economical use of power and plant.
Fig. 29. Donkey Engine Yarding.
Fig. 30. Giant Raft. In the background is a completed raft;
in the foreground a cradle in which a raft is being built.
Another method of traction where the woodland is open enough is with a traction engine. The ones employed have sixty to one hundred horse power. The great logs may be placed on wood rollers, as a house is when moved, or the logs may be hauled in on a low truck with broad wheels. The "tractor" hauls the log direct to the railway if the distance is not too great.
Fig. 31. Snow Locomotive. Takes the place of 12 teamsters and 12 horses. Minnesota.
In Northern Michigan a "snow locomotive," Fig. 31, is coming into use, which has tremendous tractive power, hauling one hundred to one hundred fifty tons of lumber over snow or ice. It moves on runners, but there is between them a large cylinder armed with teeth. This cylinder can be raised or lowered by the operator as it moves over the surface of the ground. The teeth catch in the snow or ice, and since the cylinder is heated by the exhaust steam, it melts and packs the snow for the trucks following it. The drum is six feet in diameter, with walls an inch and a half thick, and it weighs seven tons. It is used in all sorts of places where horses cannot go, as in swamps, and by substituting wheels for runners it has even been used on sand.
In the Canadian lakes there has been devised a queer creature called an "alligator," a small and heavily equipped vessel for hauling the logs thru the lakes. When its operations in one lake are finished, a wire cable is taken ashore and made fast to some tree or other safe anchorage, the capstan on its forward deck is revolved by steam and the "alligator" hauls itself out of the water across lots to the next lake and begins work there.
The greatest improvement in water transportation is the giant raft, Fig. 30. When such a raft is made up, logs of uniform length are placed together, the width of the raft being from sixty to one hundred feet and its length, one thousand feet or more. It may contain a million board feet of timber. The different sections are placed end to end, and long boom sticks, i. e., logs sixty to seventy feet long, are placed around them to bind the different sections together, and finally the whole mass is heavily chained. Such a raft has been towed across the Pacific.
LOGGING
References2
River Lumbering.
Pinchot, Primer, II, pp. 40-53.
White, Blazed Trail, pp. 5-15, 25, 38-39, 52-53, 63-65, 72-85, 91-99, 113-125, 134, 181-196, 216-229, 257, 268, 320-343, 355, 365 ff.
For. Bull., No. 34, pp. 33-41, Fox.
White, Jun. Mun., 10: 362.
Hulbert, Outl., 76; 801.
Wood Craft, 4: 55.
Smith, K., World's Work, 7: 4435.
Mechanical Methods.
World's Work, 7: 4435.
Outl., 76: 812.
Bruncken, p. 86.
Bruncken, pp. 76-87.
Munn, Cosmop., 37: 441.
Roth, First Book, pp. 133-174.
Hovey-King, Rev. of Rev., 27: 317.
Jones, Cosmop., 15: 63.
Price, World's Work, 5: 3207.
For. Bull., No. 61.
Cassier, 29: 443, April, '06.
Cosmop., 37: 445.
Rev. of Rev., 28: 319.
Chapter II.
SAWMILLING
The principal saws in a mill are of three kinds, the circular, Fig. 32, the gang, Fig. 33, and the band, Fig. 34. The circular-saw, tho very rapid, is the most wasteful because of the wide kerf, and of course the larger the saw the thicker it is and the wider the kerf. The waste in sawdust is about one-fifth of the log. In order to lessen this amount two smaller saws, one hung directly above the other, have been used. One saws the lower half of the log and the other the upper half. In this way, it is possible to cut very large logs with the circular-saw and with less waste. The circular-saw is not a perfectly flat disc, but when at rest is slightly convex on one side and concave on the other. This fullness can be pushed back and forth as can the bottom of an oil-can. When moving at a high rate of speed, however, the saw flattens itself by centrifugal force. This enables it to cut straight with great accuracy.
Fig. 32. Double Circular-Saw and Carriage.
A gang-saw is simply a series of straight saw-blades set in a vertical frame. This has a reciprocating motion, enabling it to cut a log into a number of boards at one time. It has this drawback, that it must cut the size of lumber for which it is set; that is, the sawyer has no choice in cutting the thickness, but it is very economical, wasting only one-eighth of the log in sawdust. A special form is the flooring gang. It consists of a number of saws placed one inch apart. Thick planks are run thru it to saw up flooring.
Fig. 33. Gang-Saw.
Fig. 34. Band-Saw.
The band-saw is fast displacing the other two, wherever it can be used. It cuts with great rapidity and the kerf is narrow. When first used it could not be depended upon to cut straight, but by utilizing the same principle that is used in the circular-saw, of putting the cutting edge under great tension by making it slightly shorter than the middle of the saw, it now cuts with great accuracy. Band-saws are now made up to 12 inches wide, 50 feet long, and run at the rate of 10,000 feet a minute. They are even made with the cutting teeth on both edges, so that the log can be sawed both going and coming. This idea was unsuccessful until the invention of the telescopic band-mill, Fig. 35. In this the entire mechanism carrying the wheels on which the band-saw revolves can be moved up and down, so as to bring the point where the saw leaves the upper wheel as close to the top of the different sized logs as possible.
Fig. 35. Double-Carrying Telescopic Band-Mill.
Fig. 36. Jack-Ladder, with Endless Chain. Mill in raised position for large log.
The usual modern mill is a two story building, Fig. 37, built at a convenient locality both for receiving the logs and for shipping the lumber. Whether the logs arrive by water or by rail, they are, if possible, stored in a mill-pond until used in order to prevent checking, discoloration, decay, and worm attack. From the pond they are hauled up out of the water on to a "jack-ladder," by means of an endless chain, provided with saddles or spurs which engage the logs and draw them up into the second story on to the log slip, Fig. 36.
Fig. 37. Two-Story Mill at Virginia, Minnesota, Showing Jack-Ladders and Consumer.
Fig. 38. Log-Flipper.
Fig. 39. Log-Stop and Loader. By letting steam into the cylinder, the projecting arm revolves, rolling one log over onto the carriage and holding the next one till wanted.
After the logs have entered the mill, they are inspected for stones lodged in the bark, and for spikes left by the river men, and then measured. Under the log-slip is the steam "flipper" or "kicker," Fig. 38, by means of which the scaler or his assistant, throwing a lever, causes the log to be kicked over to one side or the other, on to the log-deck, an inclined floor sloping toward the saw-carriage. Down this the log rolls until stopped by a log-stop, or log-loader, Fig. 39, a double-aimed projection, which prevents it from rolling on the carriage till wanted. This stop is also worked by steam. By letting the steam into the cylinder which controls it, one log is rolled over on the carriage and the next one held. The log on the carriage is at once "dogged," that is, clamped tight by iron dogs, the carriage is set for the proper cut, and moves forward to the saw which cuts off the first slab. The carriage is then "gigged" or reversed. This operation offsets the carriage one-eighth of an inch so that the log returns entirely clear of the saw. In the same way two or three 1" boards are taken off, the dogs are then knocked out, and the log canted over half a revolution. This is done by means of the "steam nigger," Fig. 40, a long, perpendicular toothed bar which comes up thru the floor, engages the log, and turns it over till the sawn side comes up against the knees of the carriage. The log is dogged again and a second slab and several boards are taken off. The log or "stock" as it is now called, is 10", 12", 14", or 16" thick; the "nigger" then gives it a quarter-turn, leaving it lying on a sawn side. It is dogged again, and all sawn up except enough to make a few boards. This last piece is given a half-turn, bringing the sawn side against the knees, and it is sawn up. Each board as it is sawn off is thrown by the board-flipper or cant-flipper,3 Fig. 41, on to the "live rollers," which take it to the next process. Another log comes on the carriage and the process is repeated.
Fig. 40. The Steam Nigger.
The toothed bar turns the log over into the desired position.
The saw-carriage, Fig. 42, is propelled forward and back by a piston running in a long cylinder, into either end of which steam can be turned by the operator.
As the sawn boards fall off the log, they land on "live," that is, revolving rollers, which carry them along at the rate of 200 to 250 feet a minute. Stops are provided farther along to stop the boards wherever wanted, as at the edger, Fig. 43, or the slasher. From the live rollers the boards are transferred automatically, Fig. 44, by chains running at right angles to the rollers and brought within reach of the edger man. About one-third of the boards of a log have rough edges, and are called "waney." These must go thru the edger to make their edges parallel. The edger man works with great speed. He sees at once what can be made out of a board, places it in position and runs it thru. From the edger the boards are carried to the trimmer, which cuts the length. The lumberman's rule is to "cut so that you can cut again." The so-called 16' logs are really 16' 6". The trimmer, Fig. 45, now trims these boards to 16' 1", so that if desired they can still be cut again. The trimmer may be set to cut at any desired length according to the specifications.
Fig. 42. Log-Carriage, holding quartered log in position to saw.
Fig. 43. Double Gang Edger. This machine trims off the rough edges of the "waney" boards by means of the four saws in the main frame of the machine.
Fig. 44. Automatic Steam Transfer for Timber, Lumber and Slabs. The boards are carried along by the cylinders, CCC, until they hit the bumper, B. This movement admits steam to the cylinder, CY, which raises the revolving chains or skids, which transfers the stock sidewise to other live rollers as required.
Fig. 45. Automatic Gang Lumber-Trimmer. It may be set to cut automatically to any desired length.
Fig. 46. Lumber Sorting Shed. Virginia, Minnesota.
Fig. 47. Wood is carefully and regularly piled in the seasoning-yard.
The boards are now graded as to quality into No. 1, No. 2, etc., Fig. 46, and run out of the mill, to be stacked up in piles, Fig. 47. Big timbers go directly from the saw on the rolls to the back end of the mill, where the first end is trimmed by a butting-saw or cut-off-saw which swings, Fig. 48. The timber is then shoved along on dead rolls and the last end trimmed by the butting-saw to a definite length as specified, and shoved out.
One of the most remarkable features of the modern mill is its speed. From the time the log appears till the last piece of it goes racing out of the mill, hardly more than a minute may have elapsed.
Fig. 48. Cut-off-Saw. This saw trims the ends of timbers.
A large part of the problem of sawmilling is the disposal of the waste. The first of these is the sawdust. In all first class mills, this together with shavings (if a planing-mill is combined) is burned for fuel. It is sucked up from the machines and carried in large tubes to the boiler-room and there is mechanically supplied to the fires. The slabs, once considered as waste, contain much material that is now utilized. From the live rolls, on which all the material falls from the main band-saw, the slabs are carried off by transfer chains, and by another set of five rollers to the "slasher," Fig. 50, which consists of a line of circular-saws placed 4' 1" apart. This slasher cuts up the slabs into lengths suitable for lath or fence-pickets, Fig. 49. Or they can be resawn into 16" lengths for shingles or fire-wood.
Fig. 49. Ten Saw Gang Lath Bolter. This machine cuts up material lengthwise into laths.
Fig. 50. Slab-Slasher. This machine cuts up the slabs into lengths suitable for lath or fence-pickets.
From the "slasher" the 4' 1" lengths are carried on by traveling platforms, chains, etc., to the lath-machines, Fig. 51, where they are sawn up, counted as sawn, bound in bundles of 100, trimmed to exactly 4' in length and sent off to be stored. The shingle bolts are picked off the moving platforms by men or boys, and sent to the shingle-machine, Fig. 52, where they are sawn into shingles and dropped down-stairs to be packed. Shingle-bolts are also made from crooked or otherwise imperfect logs.
Of what is left, a good part goes into the grinder or "hog," Fig. 53, which chews up all sorts of refuse into small chips suitable for fuel to supplement the sawdust if necessary. Band-saws make so little dust and such fine dust that this is often necessary.
Fig. 51. Combination Lath-Binder and Trimmer. With this machine the operator can trim the bundles of lath simply by tilting the packing frame over from him causing the bundles to pass between the saws, thereby trimming both ends at one movement.
Fig. 52. Hand Shingle-Machine. This machine is used in Sawmills in which it is desired to utilize slabs and trimmings by sawing shingles therefrom, or to saw shingles from prepared bolts.
If there is any refuse that cannot be used at all it goes to the scrap-pile, Fig. 54, or to the "consumer," the tall stack shown in Fig. 37, see p. 33.
Boards ordinarily sawn from logs are "slash-sawn," i. e., they are tangential or bastard, each cut parallel to the previous one. By this process, only the central boards would be radial or "rift" boards.
Fig. 53. Edging grinder or Hog. It cuts any kind of wood into coarse or fine chips suitable to be handled by chain conveyor or blower.
But, for a number of reasons, radial boards are better. They warp less because the annual rings cross the board more evenly. Yellow pine flooring that is rift-sawn is more valuable than slash-sawn, because the edge of the annual rings makes a more even grain, Fig. 55. Where slash-grained flooring is used, the boards should be laid so that the outside of each board will be up in order that the inner rings may not "shell out."
In sawing oak for valuable furniture or trim, the log is first "quartered" and then the quarters sawn up as nearly radially as is desired. There are various methods of cutting quartered logs, as illustrated in Fig. 56.
In making staves for water-tight barrels, it is essential that they be cut radially in the log, in order that the staves be as non-permeable to water as possible.
Fig. 54. Scrap-Pile. Oscilla. Georgia.
Fig. 55. Slash-Grain and Comb-Grain Flooring.
Fig. 56. Methods of Sawing Quartered Logs.
SAWMILLING
Fig. 57. Lumber-Kiln.
Chapter III.
SEASONING
The seasoning of wood is important for several reasons. It reduces weight, it increases strength, it prevents changes in volume after it is worked into shape, and it prevents checking and decay. Decay can also be prevented by submergence and burying, if by so doing logs are kept from fungal attacks. The piles of the Swiss Lake dwellings, which are in a state of good preservation, are of prehistoric age. Wood under water lasts longer than steel or iron under water. But for almost all purposes wood has to be dried in order to be preserved. The wood is cut up, when green, to as thin pieces as will be convenient for its use later, for the rate of drying depends largely upon the shape and size of the piece, an inch board drying more than four times as fast as a four inch plank, and more than twenty times as fast as a ten inch timber.
There are various methods of seasoning:
(1) Natural or air-seasoning is the most common, and in some respects the best. In this method, the wood is carefully and regularly piled in the seasoning-yard, so as to be protected as far as possible from sun and rain, but with air circulating freely on all sides of the boards, Fig. 47, see p. 38. To accomplish this, "sticking" is employed, i. e., strips of wood are placed crosswise close to the ends and at intervals between the boards. In this way the weight of the superposed boards tends to keep those under them from warping. The pile is skidded a foot or two off the ground and is protected above by a roof made of boards so laid that the rain will drain off.
Fire-wood is best dried rapidly so that it will check, making air spaces which facilitate ignition, but lumber needs to be slowly dried in cool air so that the fibers may accommodate themselves to the change of form and the wood check as little as possible. Good air-drying consumes from two to six years, the longer the better.
(2) Kiln-drying or hot-air-seasoning is a much more rapid process than air-seasoning and is now in common use, Fig. 57. The drying is also more complete, for while air-dried wood retains from 10% to 20% of moisture, kiln-dried wood may have no more than 5% as it comes from the kiln. It will, however, reabsorb some moisture from the air, when exposed to it.
The wood of conifers, with its very regular structure, dries and shrinks more evenly and much more rapidly than the wood of broad-leaved trees, and hence is often put into the kiln without previous air-drying, and dried in a week or even less time.
Oak is the most difficult wood to dry properly. When it and other hardwoods are rapidly dried without sufficient surrounding moisture, the wood "case-hardens," that is, the outer part dries and shrinks before the interior has had a chance to do the same, and this forms a shell or case of shrunken, and often checked wood around the interior which also checks later. This interior checking is called honeycombing. Hardwood lumber is commonly air-dried from two to six months, before being kiln-dried. For the sake of economy in time, the tendency is to eliminate yard-drying, and substitute kiln-drying. Kiln-drying of one inch oak, takes one or two weeks, quarter-sawn boards taking one and a half times as long as plain-sawn.
The best method of drying is that which gradually raises the temperature of both the wood and of the water which it contains to the point at which the drying is to take place. Care is therefore taken not to let the surface become entirely dry before the internal moisture is heated. This is done by retaining the moisture first vaporized about the wood, by means of wet steam. When the surface is made permeable to moisture, drying may take place rapidly. Curtains of canvas are hung all around the lumber on the same principle that windows in newly plastered buildings are hung with muslin. The moisture is absorbed on the inner surface of the curtain and evaporates from the outer surface. Improvements in kiln-drying are along the line of moist air operation. In common practice, however, the moist air principle is often neglected.
There are two methods in operation, the progressive method and the charge method. In the progressive, the process is continuous, the loads going in at one end of the kiln, and out at the other, the temperature and the moisture being so distributed in the kiln, that in passing from the green to the dry end, a load of lumber is first moistened, then heated, and finally dried out. In the charge system, the process is intermittent, one charge being removed before a new one is admitted. This gives the best results with high grade lumber for special uses.
A modification of hot-air-seasoning is that which subjects the wood to a moderate heat in a moist atmosphere charged with the products of the combustion of fuel.
(3) Small pieces of wood may be effectively seasoned by being boiled in water and then dried. The process seems to consist of dissolving out albuminous substances and thus allowing freer evaporation. Its effect is probably weakening.
(4) Soaking in water is sometimes used as a good preparation for air-seasoning. Previous soaking hastens seasoning. River men insist that timber is improved by rafting. It is a common practice to let cypress logs soak in the swamps where they grow for several months before they are "mined out." They are eagerly sought after by joiners and carpenters, because their tendency to warp is lessened. Ebony is water-soaked in the island of Mauritius as soon as cut. Salt water renders wood harder, heavier, and more durable and is sometimes applied to ship timbers, but cannot be used with timbers intended for ordinary purposes, as the presence of salt tends to absorb atmospheric moisture.
(5) Boiling in oil is resorted to for special purposes, both for preservation and to give strength. For example, the best handscrews are so treated. The oil also prevents glue from sticking, the most frequent cause of injury to handscrews.
(6) There are a number of "impregnation" methods of preserving timber, and their practice is spreading rapidly. Of the various preservative processes, those using coal tar creosote and zinc chloride have proved most efficient. The purpose is to force the preservative into the pores of the wood, either by painting, soaking, or putting under pressure. Such impregnation methods double or treble the life of railway ties. It is now being used with great success to preserve electric wire poles, mine-props, piling, fence-posts, etc.
Wood preservation has three great advantages, it prolongs the life of timbers in use, reduces their cost, and makes possible the use of species that once were considered worthless. For example, the cheap and abundant loblolly pine can be made, by preservative methods, to take the place of high priced long-leaf pine for many purposes.
PRACTICAL SUGGESTIONS FOR STORING LUMBER
Under the hasty methods prevalent in the mill, very little wood comes to the shop well seasoned, and it should therefore be carefully stored before using, so as to have the fullest possible air circulation around it. Where the boards are large enough, "sticking" is the best method of storage, i. e., narrow strips of wood are placed at short intervals between the pieces which are piled flat. The weight of the boards themselves helps to prevent warping. Boards set upright or on edge are likely to be distorted soon. It is often wise to press together with weights or to clamp together with handscrews boards that show a tendency to warp, putting the two concave sides together. Then the convex side is exposed and the board may straighten thus: Fig. 58. By wrapping up small boards in paper or cloth in the intervals between work on them, they may be kept straight until they are assembled.
Fig. 58. Clamping up Boards to Prevent Warping.
Another precaution to take is to be sure to plane both sides of a board if either is planed, especially if the board has been exposed to air-drying for some time.
WOOD MEASUREMENTS
Lumber is a general term for all kinds of sawn wood. Logs may be sawn into timber, that is, beams and joists, into planks, which are 2" to 4" thick, or into boards which are from ¼" to 1¾" thick. These may be resawn into special sizes.
Lumber is measured by the superficial foot, which is a board 1" thick, 12" wide, and 12" long, so that a board 1" thick, (or ⅞" dressed) 6" wide and 12' 0" long, measures 6' B. M. (board measure). Boards 1" or more thick are sold by the "board foot" which is equivalent to 12" square and 1" thick. Boards less than 1" thick are sold by the square foot, face measure. Dressed lumber comes in sizes ⅛" less than sawn lumber. Regular sizes are:
Any of these may be dressed down to thinner boards, or resawn on a special band-saw.
In ordering it is common to give the dimensions wanted, in the order of thickness, width, and length, because that is the order in which dimensions are gotten out. E. g.:
6 pcs. quar. oak, ⅞" × 6" × 3'0"
2 pcs. quar. oak, ¾" × 7½" × 15"
If a piece wanted is short the way the grain goes, the order would be the same, thus: ¾" × 11" (wide) × 6" (long). That is, "long" means the way the grain runs. It is always safe to specify in such a case. It is common when small pieces are ordered to add one-quarter to the cost for waste.
In large lots lumber is ordered thus: 800' (B. M.) whitewood, dressed 2 sides to ⅞", 10" and up. This means that the width of any piece must not be less than 10". Prices are usually given per "M," i. e., per 1000 ft.: e. g.: basswood may be quoted at $40.00 per M.
When thin boards are desired it is often economical to buy inch stuff and have it resawn.
Some lumber is also ordered by the "running" or lineal foot, especially moldings, etc., or by the piece, if there is a standard size as in fence-posts, studs, etc. Laths and shingles are ordered by the bundle to cover a certain area. 1000 4" shingles (= 4 bundles) cover 110 sq. ft. with 4" weather exposure. 100 laths (1 bundle) each ¼" × 1½" × 4'0" cover about 150 sq. ft.
There are several methods of measuring lumber. The general rule is to multiply the length in feet by the width and thickness in inches and divide by 12, thus: 1" × 6" × 15' ÷ 12 = 7½ feet. The use of the Essex board-measure and the Lumberman's board-measure are described in Chapter 4, pp. 109 and 111.
THE SEASONING AND MEASURING OF WOOD
References5
seasoning.
For. Bull., No, 41, pp. 5-12, von Schrenk.
Dunlap, Wood Craft, 6: 133, Feb. '07.
For. Circ. No. 40, pp. 10-16, Herty.
Barter, pp. 39-53.
Boulger, pp. 66-70, 80-88.
Wood Craft, 6: 31, Nov. '06.
For. Circ. No. 139.
Agric. Yr. Bk., 1905, pp. 455-464.
measuring.
Sickels, pp. 22, 29.
Goss, p. 12.
Building Trades Pocketbook, pp. 335, 349, 357.
Tate, p. 21.
