Bubinga (African Rosewood)

Bubinga (African Rosewood)

Bubinga lumber as sold today includes two species (Guibourtia tessmannii and G. pellegriniana). Bubinga is a hard and heavy wood that is grown in Cameroon, Gabon and the Ivory Coast of Africa. It would be classified as a tropical hardwood. It is widely available as lumber and veneer in the U.S. market; it is often quite expensive. (Good news: Some supplies of this wood available in North America are from environmentally responsible or sustainably managed sources.)

Bubinga trees are often very large, often reaching heights of more than 100 feet and trunk diameters of 3 feet. Logs may weigh thousands of pounds, as this is a very heavy wood. When freshly sawn, the wood has an unusual and unpleasant odor that, thankfully, disappears after drying.

The rich grain and high hardness make this wood perfect for decorative flooring and tabletops.

Other lumber species available in North America in this same genus include benge or mutenye (G. Arnoldiana), and ovangkol or ehie (G. Ehie). These relatives are much browner in color and not nearly so dense as bubinga. Bubinga logs with very irregular grain are rotary cut into veneers and are sometimes sold under the common name of kevasingo.

Processing suggestions and characteristics

Density. The density can vary quite a bit, ranging from 43 to 52 pounds per cubic foot when dry. A piece of 4/4, kiln-dried lumber that is 1-inch thick by 8-inches wide by 12-feet long will weigh 28 to 33 pounds. Northern red oak lumber of the same size would weigh about 28 pounds.

Drying. This wood must be dried very slowly, slower than red oak, as it is quite prone to checking. Warp can also be a problem at times. Flatsawn lumber shrinkage is roughly 9 percent.

Gum pockets and streaks are often seen. This gum cannot be set (or hardened) in the kiln drying process.

Gluing and Machining. Reports are that this wood requires the some gluing skill, as do all dense species, in order to achieve a strong glue joint, just as red oak requires. However, the gum pockets, if present, can interfere with good gluing.

Machining is actually a little easier than the high density would suggest. Nevertheless, it is a dense wood and requires sharp tools, correct MCs, and proper feed rates. The wood does not have minerals that would lead to rapid dulling, but the high density does indeed result in rapid dulling. Rake angles may have to be decreased slightly from oak values. Diamond tipped saws would seem worth considering.

Stability. This wood is similar to southern red oak in stability, requiring a 3 percent MC to produce a 1 percent size change in the tangential (parallel to the rings, or the width of a flatsawn pieces of lumber) direction. Across the rings (radially), a 4 percent MC change results in a 1 percent size change.

Strength. Because of the wide range in density, strength properties also vary. As much of the lumber imported into the U.S. is rather dense, the strength (MOR) will be about 22,600 psi, the stiffness about 2.48 million psi, and the hardness about 2690 pounds. This is considerably stronger, stiffer and harder than northern red oak (14,300 psi, 1.82 million psi, and 1290 pounds).

Because of the high density, pre-boring of holes for nails and screws is essential. Nail and screw holding power, even with pre-boring, is very high.

Color and Grain. The sapwood is whitish in color. The heartwood is medium red-brown or red to reddish-brown in color, with lighter red to purple veins. Upon exposure to light and air, the wood becomes yellow or medium brown with a reddish tint, and the veining becomes less conspicuous. The surface appears somewhat lustrous. The wood can be polished easily.

The grain texture ranges from fine to very fine, and is even. The grain may be straight or, at times, interlocked. Interlocked grain causes warp when the moisture content changes.

Gum streaks and pockets are present, but seem to cause no serious processing problems except in gluing. However, the gum may exude from the wood over time.

The heartwood is reported to naturally resistant to decay and most insects.

This post appeared first on http://www.woodworkingnetwork.com

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