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October 1, 1998 Issue


October 15, 1998 Issue

October 1, 1998 Issue


What Wood Is That?

From the Materials Handbook

An Encyclopedia for Managers, Technical Professionals, Purchasing and Production Managers, Technicians, Supervisors, and Foremen

Have you ever wondered about some of the exotic woods that turn up in wooden boatbuilding? Well, here's some sober straight goods on what some of these are from an engineering viewpoint.

TEAK: The wood of the tree Tectona grandis, of southern Asia. It resembles oak in appearance, is strong and firm, and in England is called Indian oak. It contains an oil that gives it a pleasant odor and makes it immune to the attacks of insects. It is used for boxes, chests, home furnishings, and for woodwork on ships. The color is golden yellow, the grain is coarse and open, and the surface is greasy to the touch. It is one of the most durable of woods, and also has small shrinkage. The weight is 40 lb. per cu ft. In Burma large plantations grow teak for export. Trees grow to a height of 100' with a diameter of 3'. The growth is slow, a 2' tree averaging 150 years of age.

The wood marketed as African teak, known also as iroko, is from the tree Chlorophora excelsa, of West Africa, and is unlike true teak. It is a firm, strong wood with a brownish color and a coarse, open grain. The weight is somewhat less than teak, and it is harder to work, but it is resistant to decay and to termite attack, and is used in ship construction.

Surinam teak is the wood of the tree Hymenea courbarzl of the Guianas and the West Indies. It is also called West Indian locust. The wood is dark brown in color, hard, heavy, and difficult to work. It is not very similar to teak and not as durable.

Seacoast teak, or bua bua, is a hard, yellow, durable wood from species of the tree Guettarda of Malaya. Australian teak, from New South Wales, is from the tree Flindersia australis. It is yellowish red in color. close-Brained. and hard with an oily feel resembling teak, but more diffi-cult to work. In wood, of Burma, also called eng teak, is from the in tree, Dipterocarpus tuberculatus, from which gurjun balsam is obtained. The wood is reddish brown; it is not as durable as teak.

Two woods of Brazil are used for the same purposes as teak: the itauba, Silvia itauba, a tree growing to a height of about 75' in the upland forests of the lower Amazon, and itauba preta, Oreodaphne bookeriana, a larger tree growing over a wider area. The first is a greenish-yellow wood with compact texture and rough fiber, formerly prized for shipbuilding. The second resembles teak more closely, and is used for cabinetwork.

KHAYA: A class of woods from trees of the genus Khaya, growing chiefly in tropical West Africa and known commercially as African mahogany. The woods closely resemble mahogany, but they are more strongly figured than mahogany, are slightly lighter in weight, softer, and have greater shrinkage. The pores are larger, and the wood coarser. The wood is used for furniture and store fixtures, musical instruments, and paneling. It is not as suitable for patterns as mahogany.

African mahoganies are marketed under the names of the shipping ports, as the shipments from the various ports usually differ in proportion to the different species cut in the region. The chief wood of the genus, from which the native name Khaya derives, is known commercially as dry zone mahogany, K senegalensis. It is also known as kail and oganwo. It grows from Gambia to Angola on the west coast and eastward to Uganda. The heart wood is dark reddish brown, and the thick sapwood is grayish to pinkish red.

The most favored commercial wood is that of the red khaya, or red mahogany, K. ivorerlsis, known locally as dukuma and dubini. This wood is highly figured, with interlocking grain, and when quartered shows a ribbon figure with alternate light and dark stripes. It comes chiefly from the Ivory Coast, Ghana, and Nigeria. Sassandra mahogany is chiefly this species. Duala mahogany is chiefly white mahogany, K. anthoteca, known also as diala, krala. and mangona. The wood is lighter in color but tinged with red. Big-leaf mahogany, K. grandifolia, has a reddish-brown color. Much African mahogany is cut into veneer, and the standard thickness for the face veneer is 1/28".

Gaboon mahogany and Port Lopez mahogany are chiefly okume wood, from the tree Aucoumea klaineana of the Guinea coast. The tree belongs to the family Meliaceae to which khaya belongs, and the wood resembles African mahogany but is lighter in weight and softer. It is light pinkish brown in color. It is shipped chiefly to Europe where it is used for furniture, chests, boxes, and boats. Cola mahogany, from the Ivory Coast and Ghana, is niangon, Tarrietia utilis. The heartwood is light reddish brown, and the wood shows a herringbone figure on the quartered surface. It is heavier than khaya, and the pores are larger and more numerous. Cherry mahogany, or makore, is a plentiful wood on the Ivory Coast, Ghana, and in Nigeria. It is from the tree Minusops heckelii. The wood is dark reddish brown without tigurc. It is heavier than khaya and is finer in texture.

SAPELE: The figured woods of vari-ous species of trees of tropical Africa which are mixed with khaya and exported from West Africa as African mahogany. Sapele woods are harder and heavier than red khaya, but shrink and swell more than khaya with changes in moisture. They are also darker in color with a purplish tinge. Sapele ma-hogany, also called scented mahogany and West African cedar, is from thc Entandrophragma cylindricum, a very large tree growing on the Ivory Coast and in Ghana and Nigeria. On the Ivory Coast it is called aboundikro.

Another species, E. angolense, is called Tiama mahogany on thc Ivory Coast, and in Nigeria is known as brown mahogany and gedunohor. A less heavy wood, from thc tree E. utile, is known on the Ivory Coast as Sipo ma-hogany and in thc Cameroons as Assie mahogany. It is one of the chief woods exported as mahogany from the Cameroons. The wood known on the Ivory Coast as heavy mahogany and omu in Nigeria is from the tree E. candollei, and is much heavier than other sapeles.

Nigerian pearwood, from species of Guarea, notably G. cedrata and G. thompsonii, is also exported as African mahogany. The woods are more properly called guarea. The color is pale pink to reddish. The weight is about the same as sapele. The wood is of a finer texture than khaya, but it is not figured like sapele or khaya. Another wood marketed as African mahogany is lingue, from the tree Afzelia africana of the west coast of Africa from Senegal to Nigeria. The wood is light brown, turning dark when seasoned, and is beautifully figured.

LAUAN: The wood of trees of several genera of the Philippines, Malaya, and Sarawak, known in the American market as Philippine mahogany. The woods resemble mahogany in general appearance, weight, and strength but the shrinkage and swelling with changes in moisture are greater than in the true mahoganies.

The lauan woods are used for furniture and cabinet woods, paneling, and for boatbuilding. The lauans belong chiefly to the genus Shorea, and the various species have local or common names. The so-called dark-red Philippine mahogany is tangile, S. polysperma, and red lanan, S. negrosensis. Tangile is also called Bataan mahogany, and has the closest resemblance to true mahogany of all the species. The thick sapwood is light red, and the heartwood dark brownish red. It has greater tendency to warp than mahogany. Red lauan has larger pores, but is favored for boat construction because of the large sizes available. Tiaong, from the S. teysmanniana, resembles tangile but is lighter and softer. Almon, from the tree S. eximia, is harder and stronger than red lauan or tangile, but is coarser in texture and less lustrous.

White lauan is from a different genus of the same family and is Pentacme contorta. It has about the same mechanical properties as tangile, but is gray with a pinkish tint. Mindanao lanan, P. mindanensis, is quite similar but is lighter and softer. Mayapis, from the tree Shorea palos, is coarser in texture than tangile and is subject to warping and checking like red lauan. It is intermediate in color, and the light-colored wood is markered as white lauan, while the dark wood is sold as red lanan. Yellow lanan is from the trees kalunti, S. kalunti, manggasinoro, S. philipensis, and malaanonang, S. Polita. Yellow lauan is yellowish in color and has lower strength and greater warpage than other lauans.

Bagtikan, from the tree Parashorea malaanonan, is reddish gray in color, not lustrous, but it is heavier and stronger than the other lauans. Sometimes mixed with Philippine mahogany is the wood known as lumbayan, from an entirely different family of trees. It is from the tree Tametuz javanica. The thick sapwood is light gray in color and the heartwood reddish. The weight and strength are about equal to tangile but the pores are larger. When marketed separately, it is a more valuable wood than the lauans for furniture manufacture.

The reddish woods from Sarawak, Sumatra, and Malaya known as meranti, or morenti, are Shorea species of the lauan types. In the East Indies morenti is used for barrels, casks, and tanks for palm oil. Similar woods from North Borneo are called seraya, or known as Borneo cedar or Borneo mahogany. The Shorea trees yield Borneo tallow and dammar. Merawan is a wood from various species of trees of the genus Hopea of Malaya. It is valued for furniture and interior work. Much of the so-called mahogany normally shipped from the Philippines is Apitong, the wood of the tree Dipterocarpus grandiflorus also grown in Borneo and Malaya. The wood weighs 441b per cubic foot.

George S. Brady, Materials Consultant (Retired)

Henry R. Clauser, Materials Consultant, Former Editor, Materials Engineering

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October 15, 1998 Issue


Hollowood

By Paul Burni

Hollowood veneered tubing is a new, engineered wood product constructed of thin plies of poplar 1/50" to 1/16" thick which are bonded together by a high strength, waterproof polyester resin adhesive. The fourth, outside ply is faced so that the grain runs the length of the tube. An extensive family of domestic and ex-otic hardwoods is available for the outside ply. The total wall thickness is approximately 1/8" making a wooden tube that is lightweight but unbelievably strong. Hollowood is available in 16 different diameters and in 8' lengths.

Cutting Hollowood is just as easy as cutting small stock such as molding or trim. Using a fine toothed crosscut blade in a table saw or a miter box seems to work best. Because it is round, any jig or fixture that will help support the stock and keep it from rotating during the cut will be safer and will result in a cleaner, more accurate cut. A band saw does a good job but the finish cut may be a bit irregular unless a very fine toothed blade is used and the stock is supported with a hold down. A hand miter box will obviously be somewhat slower.

Brad point, Forstner or spade drills work best in Hollowood because their center point will lead into the stock allowing the outside edges to make the cut. Be care-ful not to force the bits or the chance of break out on the reverse side will be increased. The best way to prevent breakout is to use a scrap wood plug on the inside of the tubing during drilling operations. For larger diameter holes, a fly cutter with a pi-lot and a narrow cutter may be used at slow speed in a drill press and with the work suitably fixture to prevent movement.

Hollowood is real wood so any good glue may be used to glue it. We recommend Gorilla Glue for its superior strength and waterproof qualities. Fixtures, and supporting blocks are useful when bridging seams or joints. Special circumstances may dictate the need for special adhesives such as epoxies.

Any type of finishing system can be used on Hollowood. Keep in mind that the outer ply is real wood in veneer form. This special veneer is able to accept any of today's modern finishes including lacquer. Lightly sand the exterior face of the Hollowood tube with 320 grit paper to prepare the surface and then wipe with a tack rag to remove all dust. For the open-grained woods such as oak and mahogany start with a sanding sealer. Follow the manufacturer's instructions with each finishing material. We have found that it is a good idea to use the same manufacturer all the way through the finishing process. Sometimes, products from different manufacturers differ enough to give inconsistent results when used together.

The wall thickness of Hollowood is designed to be approximately 1/8" with the diameters increasing in 1/2" increments from 1-1/2" to 4-1/2." New diameters are constantly being added; particular diameter requirements may be available soon. Remember, Hollowood is real wood so dimensional tolerances of +/- 1/64" for both the wall thickness and the inside and outside diameters apply.

Is Hollowood strong? An official test report from Gougeon Brothers stated, "...a piece of wood tube 1-1/2" diameter and 10" long with standard 1/8" wall thickness weighing less than 2 oz., when placed on end could support an ultimate load of about 3,000 lbs." When Gougeon conducted a simple support test with a specimen wood tube 2-1/2" diameter, 30" long with 1/8" wall thickness weighing under l0 oz., it supported up to 500 lbs. over a 28" span.

Hollowood is available in 8' lengths and in many veneers. For some design ideas and techniques send for our booklet: Hollowood Idea Collection, $4.50 post-paid in the US.

Brand New, 6125 Pedernal Ave., Goleta, CA 93117. (800) 964-8251.



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