THE BENDING OF WOOD Curved members of wood are used for a wide variety of purposes, some, like boat planking, having a small amount of deformation, others, like tennis rackets, a severe deformation. Curved members can be produced by cutting the part out of a solid piece, a practice commonly followed in Chile in making curved chair legs and chair backs, and even wagon wheel felloes. They may also be produced by bending a single piece or by bending and gluing laminations sufficient in number to produce the required thickness. When curved members are cut from solid stock they are subject to splitting and breaking because the direction of the grain does not follow the curvature of the piece, a factor that limits the amount of curvature that can be obtained. Furthermore, this practice is very wasteful of material. Single piece bent members are much stronger than parts cut to curvature and are not inclined to split or break across the grain. The properties of laminated members are similar to single piece-bent members but are more expensive and difficult to produce in quantity. In making single piece bent members the stock must be softened to permit the required de formation, the usual agencies being steam or hot water. Wood can be stretched only a small amount, about 1 percent, without tension failure. The shortening or upset that can be brought about, however, is much greater. Because of the relation between attainable tensile and compressive deformations, it is necessary, when bending involves severe deformation, that most of the deformation be forced to take place as compression. This is accomplished by the use of metal straps on the convex side of the piece which prevent the elongation of that side during the bending operation and consequently result in compression and upset of the fibers on the concave side. Special appliances and skillful manipulation are necessary to get proper action from the straps and to prevent the compression from becoming localized, thus producing irregularities of curvature and disfiguring wrinkles. Some species can be bent more successfully than others, and generally the hardwoods are better than the softwoods. Most species can be bent to some degree but only a few can be given very severe bends. The art of bending single piece stock has not been developed in Chile in those fields where it would be most advantageous, particularly in the furniture and vehicle industry. In furniture factories bending could be used to produce curved members for chair stock, particularly chair backs, legs, rungs, and arms. This practice is especially suited to those styles and types of furniture that are, duplicated in quantity. There should also be a good market for bent rims for the wheels of wagons, carts, and other vehicles in place of the hewn felloes now used. FOREST INDUSTRIES SUGGESTED LOGGING AND MILLING TECHNIQUE FOR CHILE1 The seasonal aspect seems to affect logging chiefly because oxen are used and forage is lacking in the winter. It is said that felling is a winter practice to minimize breakage and loss from stain, decay, and insects. It is doubtful, however, that breakage is influenced much by the season of felling, and if logs are decked or not sawed until summer, it is questionable that the other losses are greatly reduced. Probably ground conditions are better for hauling during the summer or dry season than in winter. Manpower is relatively abundant in winter, but not in summer. The prevailing pattern is to fell trees and make logs (chiefly with the ax) during the winter or wet season, haul and mill chiefly during the summer, and ship lumber to local sales outlets during the summer. In visualizing a program looking toward efficient milling operations consideration is given to possible types of operations, degree of mechanization, size, etc. Mountainous areas lacking access development plus comparatively heavy stands of large trees have always been exploited by medium to large-sized operations, the main reason being that development, chiefly transportation, requires capital and engineering knowledge beyond the reach of small operators. Since apparently more than 95 percent of the production is from small mills, evidently the forested area has roads suited to ox carts or other vehicles. Because we lack knowledge of important details affecting operations in Chile, we are not justified in going very far in suggesting if emphasis be given to a few medium mills as contrasted to many small ones, but there is less chance of losing heavily on small ventures than on large ones, an argument more important from the investment angle than from that of overall policy. If, after digesting factual data on installation costs against operating performance of medium and small mills, it is decided to install several medium ones, their combined production will still be a minor part of the total. The main problem will center around improving the efficiency of small mills. We suggest the following as a pattern of small mill technique, with the proviso that no one definite set of instructions and type of equipment can be considered as best adapted to all variations encountered. Felling: If fallers can be hired during the summer, shift to summer cutting. This should give less degrade than winter felling and storage until sawed. Bucking: This involves one of the two radical changes from current practices. Instead of cutting with an ax logs of 12-foot length, cut the tree with a saw into log lengths permitting complete utilization of the merchantable length. We do not know if this should conform to United States practices, such as 8', 10', 12', 14', and 16', etc., or be modified, but the waste from cutting with an ax a rigid length justifies changing the entire practice, involving reorientation in marketing as From a memorandum prepared by C. J. Telford, Forest Products Laboratory, Madison, Wisconsin. It should be remembered that the suggestions made here are by men who have no direct knowledge of Chilean conditions. Chile needs logging and sawmill engineers familiar with both modern methods of production and with Chilean conditions who could make and apply the results of needed studies of logging and milling production. well as production. Current practice puts an extra drain on production first by wasting a foot for each scarf in ax cutting even if the 12-foot length is correctly adhered to, more if the chopper chooses to cut where lack of limbs or other conditions facilitate cutting. The rigid single length penalty results from inability to use completely the total merchantable length in each tree. In a 12-foot length the probable average waste would be 6 feet per bole. Log transportation: One of the most efficient practices possible for small mills is to confine the operation to short log hauls, timed if possible to place logs directly at the deck. Short hauls are insured by moving the mill to the timber with direct delivery to the deck. In a mountainous terrain mill sites cannot be chosen by a formula based on ideal log hauling distances, but are restricted to give down grade log hauls, adequate site room, and suitable out haul conditions. We suggest that log hauling be planned and timed to place logs directly on deck, but backed up by some yard decking to provide a reserve to take the overflow when deliveries exceed drain. As to details of transportation, we are not in position to urge any drastic change from the present system, but some means must be found to make it possible to bring in extra large logs which now appear to be beyond the capacity of the single yoke ox cart technique. Our suggestion is that logs be slid or rolled by hand down the very steep slopes combined with ground skidding with oxen where possible. Provision must be made that logs do not get out of control and overrun the beasts. Dependence can be placed on driver skill plus animal intelligence where horses are trained for such skidding, but oxen are neither nimble nor intelligent to the degree required. Various means are used to brake logs on steep pitches such as wrapping chains around them, snubbing with a wrap around a tree, etc. The ground skidding is used only to bunch logs to a trail where carts can be used. In order to insure getting out the larger logs, it may be necessary to use the high wheel carts rather than the oversized bummer now used, underslinging them and putting as many yoke of oxen on as required. We cannot outline the marginal hauling zones, yet this is a vital problem for each operation. If 5 M board feet per acre is harvested and the total cut at a set is 500 M board feet, 100 acres will be the unit per set and hauls should not need to be excessive, but as mentioned above mountainous terrain limits mill sites and penalizes hauling. Milling: No radical changes are envisioned over present practices, but we would emphasize that the rate of production is largely a matter of power available to the headsaw. The mill plan suggested gives an efficient use of men and machines. We recommend a steam engine and boiler of around 100 horsepower capacity. Slab-burning ones of this capacity weigh about 8 or 9 tons, are on wheels, but are not self-propelled. The problem of moving can be serious, but we visualize a road being built good enough to permit efficient out haul of lumber by truck, hence it could be made to serve in moving, the truck being the pulling unit. With this power and in these large logs it should be possible to cut 1 M board feet per hour. In Lumber could be transported from mill to pile, if air drying is done at the mill, with ox cart and lumber prop, as shown in Miscellaneous Publication No. 509, page 23, figure 12. If hauled green to a shipping point or concentration yard, package piling (fig. 15) might be employed. any event certain separations are made. In small operations such separations must be kept at a minimum because degrade of sun-exposed green boards is excessive, and with many separations a correspondingly higher portion of the cut is exposed. Common separations at small mills are species and thicknesses but may also include lengths, widths, and grades. The floor plan and other details for a portable mill to produce 1 M board feet per hour, in lengths 16 feet, are attached. Alternative plans are given in Miscellaneous Publication No. 509. Approximate speeds: Log haul-up 100 lineal feet per minute Saw 550 r.p.m. Blower 2800 г.p.m. Edger saws 2000 r.p.m. Slab saw 850 r.p.m. Main conveyor 60 lineal feet per minute The conveyor extends from under the saw to the burner. It takes the sawdust from the headsaw and edger; the slabs, edgings, and sawed stock up to 2 inches in thickness. Sawed stock is pulled from the trough at a point between edger and burner where the conveyor is adequately above ground to permit package piling by a man on a platform alongside the conveyor. Thick-sawed stock is pushed over the rolls to the timber dock. The conveyor is open from a point just ahead of the edger saws, thence to the burner. The tail sawyer pushes slabs and edged stock 2 inches thick or less into the conveyor, and feeds unedged stock to the edger. A baffle plus gravity at the rear of the edger could be used, thus dispensing with the tail edgerman, but this is not outlined in the drawing. Instead the tail edgerman puts edged stock and edgings into the trough. The fireman can pick out the required amount of slabs and edgings and cut them to length on the saw beyond the firebox. The platform man pulls out stock and piles it in loads off the ground so that the vehicle backs under. The slope of the conveyor is such that from under the saw it does not rise above the rear edger table level at a distance of about 18 feet back of the edger saws. A blower has been found necessary where sawdust is burned. The fire should be at least 75 feet from the mill, and in setting up consideration should be given to the prevailing wind direction so as to minimize fire hazard and smoke nuisance. The blower pipe can be made of boards nailed to form a square box about 8 inches on a side in cross-section and covered with dirt. The outlet under the firepit, however, should be of metal, and provision must be made that this outlet does not become choked with sawdust. A simple method is to pile rocks very loosely at the outlet so that the air is forced through the chinks heat-resistant rocks are required. The simplest burner enclosure is a single wall between the fire and mill about 20 feet in height of corrugated metal siding. ever, the entire pit can be walled as suggested in Miscellaneous Publication No. 509. A simple chain is suggested for the conveyor with links about as indicated in the figure. At 4-foot intervals hardwood scrapers or lugs are fixed by running the strip through the link. The exact spacing will depend upon the type of sprocket used, the essential point being that the rakers must never engage the sprocket lug. At the pit end the chain should not extend over the fire area, but a metal trough or rails provided to carry the refuse beyond the chain, that is, the refuse empties from the conveyor into the inclined trough or similar device and slides down and away from the conveyor. How At the deck end the reserve logs can be stored on skidways along both sides of the track for the tram car, remembering that it is timeconsuming to roll logs. We suggest that skidways do not reach back from the track more than 20 or 30 feet. Main dependence is placed on deliveries directly to the deck. For large logs an overhead log turner takes the strain off both n and equipment. Turn down blocks will also ease the shocks and work cellaneous Publication No. 509, fig. 11). A mill of this design and power should produce at least 1 M board per hour in 10 logs to the M board feet of timber. The normal crew is 9 men, as follows: 2 deck men, one dogger-setter, 1 sawyer, the tail sawyer-edgerman, the tail edgerman, the fireman, the lumber piler, and a man on the timber dock. The latter can help at the deck end when logs must be taken from skids along the tramway. If piling is done at the mill, two men are needed to pile. Transportation from mill to pile (if oxen are used, we assume the units must be about quadrupled) requires at least a man and horse or truck. Mill equipment costs approximately as follows: One 100 H.P. boiler-engine on wheels.... $ 4000 One husk with topsaw frame, carriage and track 1600 One 3-saw edger at least 32" inside width: 4 headsaws (two 56-inch insert-point, two 40-inch 350 150 550 120 50 125 1 log haul-up rig, rails.. 1 log turner... Shafting, pulleys, belts, rolls, saw-fitting equipment. Conveyor chain, gears, pulleys. 300 175 300 400 Total, exclusive of building costs. $ 8120 $ 2500 Truck-trailer for lumber haul...... Transporting lumber from mill to shipping point: The second modification of current practices is that a truck haul for lumber to shipping point is suggested in lieu of the 500 board feet per load, 1-mileper-hour ox cart. Trailers should be used where possible. The 1-1/2ton truck plus dual-wheel trailer is loaded with about 8-1/2 tons of lumber under conditions prevailing in the United States. Re Concentration yard: If only air-dried stock were handled and transportation from portable mill to concentration yard a year-long possibility, a relatively cheap and simple setup is adequate. A small inventory of rough dry stock is maintained at the yard, but the bulk of the rough stock is held in the pile at the sawmill until needed. working this rough stock to finished material is done on order and only the small percentage of below or above current shipping grade items is stored in a dry finish shed. Such a setup includes a sorter chain and table, trimmer, ripsaw, resaw, and planer, and limited storage capacity, usually under roof. If all year mill to yard transportation is not assured, the rough lumber inventory at the planer must be adequate to carry over non-hauling periods. If items are made that are destined for interior use, such as ceiling, flooring, etc., dry kilns and considerable dry storage shed room must be provided and a moulder and possibly a flooring machine added. In the case of a dry kiln a heating plant becomes necessary; for other setups, if available, electricity or power other than steam can be used. In order to give definiteness to the estimates, it is assumed that as delivered by small mills the lumber is green and unsorted. It is unloaded on a sorting chain provided with a Canadian trimmer. If a kiln is used, that part of the stock to be kiln-dried is sorted and loaded directly on kiln trucks from the chain. The balance is sorted, packaged, and taken to the air-dry yard to be piled. That portion going through the kiln is bulk-piled in the rough-dry shed. If no kiln is used, the green lumber is put on the sorter chain direct from receiving |