Machinery's Handbook, 31st Edition
384 Wood of treated wood and causing mechanical fasteners to corrode. Preservative salt-retention levels required for marine protection may reduce bending strength by 10 percent or more. Density of Wood.— The following formula can be used to find the density of wood in lb/ft 3 as a function of its moisture content. . . G M G M 624 1 0009 1 100 # # ρ = + + a a k k where r is the density, G is the specific gravity of wood, and M is the moisture content expressed in percent. Table 2. Weights of American Woods, in Pounds per Cubic Foot
Species
Species
Species
Alder, red Ash, black
46 28 Douglas fir, Rocky Mt. region
35 30 Oak, red 54 35 Oak, white 53 44 Pine, lodgepole 56 37 Pine, northern white 45 25 Pine, Norway 46 27 Pine, ponderosa 45 35 Pines, southern yellow: 50 34 Pine, loblolly 50 28 Pine, longleaf 41 29 Pine, shortleaf 63 51 Pine, western white 61 … Poplar, yellow 48 36 Redwood 58 48 Spruce, eastern 47 34 Spruce, Engelmann 54 40 Spruce, Sitka 62 45 Pine, sugar
64 44 63 47 39 29 36 25 42 34 45 28 53 36 55 41 52 36 52 25 35 27 38 28 50 28 34 28 39 23 33 28 52 34 47 37 58 38
52 34 Elm, American 48 41 Elm, rock 46 38 Elm, slippery 43 26 Fir, balsam 54 45 Gum, black 57 44 Gum, red 50 38 Hemlock, eastern 36 31 Hemlock, western 42 26 Fir, commercial white
Ash, commercial white
Ash, Oregon
Aspen
Basswood
Beech Birch
Birch, paper Cedar, Alaska
Cedar, eastern red Cedar, northern white Cedar, southern white Cedar, western red
37 33 Hickory, pecan 28 22 Hickory, true 26 23 Honeylocust 27 23 Larch, western 45 35 Locust, black 55 30 Maple, bigleaf 49 28 Maple, black 46 24 Maple, red 51 32 Maple, silver 38 34 Maple, sugar
Cherry, black
Chestnut
Cottonwood, eastern
Cottonwood, northern black
50 38 Sycamore 45 33 Tamarack 56 44 Walnut, black
Cypress, southern
Douglas fir, coast region
Source: United States Department of Agriculture Machinability of Wood.— The ease of working wood with hand tools generally varies directly with the specific gravity of the wood; the lower the specific gravity, the easier the wood is to cut with a sharp tool. A rough idea of the specific gravity of various woods can be obtained from the preceding table by dividing the weight of wood in lb/ft 3 by 62.355. A wood species that is easy to cut does not necessarily develop a smooth surface when it is machined. Three major factors, other than specific gravity, influence the smoothness of the surface obtained by machining: interlocked and variable grain, hard deposits in the grain, and reaction wood. Interlocked and variable grain is a characteristic of many tropical and some domestic species; this type of grain structure causes difficulty in planing quarter sawn boards unless careful attention is paid to feed rates, cutting angles, and sharpness of the knives. Hard deposits of calcium carbonate, silica, and other minerals in the grain tend to dull cutting edges quickly, especially in wood that has been dried to the usual in service moisture content. Reaction wood results from growth under some physical stress, such as occurs in leaning trunks and crooked branches. Generally, reaction wood occurs as tension wood in hardwoods and as compression wood in softwoods. Tension wood is particularly troublesome, often resulting in fibrous and fuzzy surfaces, especially in woods of lower density. Reaction wood may also be responsible for pinching saw blades, resulting in burning and dulling of teeth. The Table 3 rates the suitability of various domestic hardwoods for machining. The data for each species represent the percentage of pieces machined that successfully met
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online