Wood Explorer: Jarrah

June 06, 2019

 

There are many species that are in the Eucalyptus genus. Some are small and produce leaves for floral arrangements; others (including jarrah, and also blue gum, karri and Tasmanian oak) produce excellent timber and lumber products. Jarrah, Eucalyptus marginata, is a dark red wood with outstanding strength and stiffness. This species, also called Swan River mahogany in the past, is found along the coastal area of Southwest Australia, and is imported into the U.S., primarily into West Coast ports.

The tree itself can be extremely large — up to 150 feet tall and often over 5 feet in diameter —  which means a lot of clear lumber. In fact, this species is one of the most important timber species in Australia. Oftentimes, lumber and timbers are received from old buildings being demolished.

In addition to the properties mentioned, it has natural decay resistance.

Historically, the leaves and bark of this tree provided cures for fever, colds, headaches, skin diseases and snakes bites.

In addition to traditional uses for furniture and cabinets, if you need a beautiful red hard floor or are making furniture for outdoor use, including hot tubs, this is the premium species. Jarrah is also prized for percussion instruments and guitar inlays. Because of its natural color, the wood can be finished with wax alone to achieve a durable finish.

PROCESSING SUGGESTIONS AND CHARACTERISTICS

Density

The specific gravity of green lumber is 0.68, or about 42 pounds per cubic foot. The lumber weight, when dried to 6 percent MC, is r over 4 pounds per board foot.  This is nearly 20 percent heavier than red oak.

Drying and Stability

This wood dries slowly often with considerable risk of warp. Generally, the wood is dried similarly to American oak. Supplies intended for North America would always be dried before being exported.

Tangential shrinkage (the width in flatsawn lumber) is high – about 9 percent; radial, 6 percent.

Movement in service is moderately high, especially when compared to native U.S. species. A 1 percent size change tangentially can occur with 2.6 percent MC change; radially, with a 4 percent MC change. As a result, correct final MC is essential to avoid moisture changes and subsequent size changes in-use.

Gluing and Machining

Unless tools are very sharp, this is a difficult species to machine, due to its high density. Interlocked grain also means that machining equipment must be in perfect operating order to avoid pockets or streaks of chipped grain.

(With interlocked grain, the wood fibers are at a slight angle to the vertical in a number of adjacent annual rings and then reverse the angle in the next few succeeding rings, and this pattern is repeated. As a result, the wood appears to be ribbon-striped, but a planer will always be planing part of the surface “against the grain.”)

Gluing is moderately difficult, as with most dense species. Gluing soon after machining the mating surfaces is essential, as is common with dense woods, to avoid moisture changes and non-flat surfaces.

Strength

Due to its high density, jarrah’s strength and stiffness are exceptionally high. For dry wood, the ultimate strength (MOR) is 16,200 psi, stiffness (MOE) is 1.88 million psi and hardness is 1910 pounds. Comparative oak values are 14,300 psi, 1.82 million psi, and 1290 pounds. The high hardness makes it a good choice for flooring, especially industrial flooring, and other high impact, high strength areas. High natural decay resistance makes this a good choice for boardwalks and exterior flooring, as well as outdoor furniture. Bending stock is another good application.

Nails and screws have excellent holding power, but predrilling of holes is necessary in most cases.

Color and Grain

Heartwood is dark red brown, darkening somewhat with exposure. Gum pockets are occasionally found. The surface texture is somewhat coarse with many small open pores. Surfaces would not be consider exceptionally smooth. The grain is usually quite straight, although sometimes there may be some interlocked grain.

 

Author: Gene Wengert

Lear more at: https://www.woodworkingnetwork.com/wood/wood-explorer/jarrah