Wood species
Obeche wood
Obeche is a hardwood (Triplochiton scleroxylon). At 12% moisture content it has a Janka hardness of 430 lbf (1,913 N) and it weighs about 22 lb/ft³ (356 kg/m³), 1.9 lb (0.84 kg) per board foot.
Key numbers
- Janka hardness, 12% MC
- 430 lbf (1,913 N)
- Green: 420 lbf (1,868 N)
- Weight at 12% MC
- 22 lb/ft³ (356 kg/m³)
- 1.9 lb per board foot
- Specific gravity (oven-dry weight)
- 0.30 on green volume
- Shrinkage, green to oven-dry
- 5.4% tangential
- Radial 3.0%, volumetric 9.2%
One source: USDA Forest Products Laboratory, collected from the world literature (its Tables 5-5 and 4-4)
Why: From the USDA Wood Handbook, which collected these values from the world literature; obeche's density is worked from its specific gravity with the Handbook's own equations.
How much obeche moves
A 12 in wide flatsawn board of obeche that goes from 6% to 12% moisture content swells about 0.14 in (about 1/8 in, 3.4 mm). Quartersawn, the same board moves about 0.07 in (about 1/16 in, 1.9 mm). Flatsawn faces move 1.8 times as much as quartersawn ones, because the wood shrinks 5.4% around the growth rings but only 3.0% across them.
Worked from the Wood Handbook's shrinkage values (Table 4-4) with its Eq. 13-4; the Handbook gives no movement coefficients for imported woods. Individual boards vary: the Handbook gives shrinkage a coefficient of variation of about 15% (p. 4-11).
Color, grain and working
- Color
- Creamy white to pale yellow, with little difference between heartwood and sapwood.
- Grain and texture
- Uniform medium to coarse texture, usually interlocked grain.
- Working and character
- Fairly soft and light. Dries readily, works easily, glues well and takes nails and screws without splitting. Not resistant to decay.
- Uses
- Veneer and core stock, furniture parts, millwork, patterns and boxes.
Adapted in our own words from the Wood Handbook, Chapter 2, p. 2-32.
Strength
Bending strength is the modulus of rupture (MOR); stiffness is the modulus of elasticity (MOE). Values for obeche from Wood Handbook Table 5-5b (p. 5-23), which the Handbook says were collected from the world literature, on clear, straight-grained specimens. Knots and cross grain make lumber weaker than these clear samples (Handbook Chapter 5).
| Property | Green | 12% MC |
|---|---|---|
| Bending strength (MOR) | 5,100 psi (35 MPa) | 7,400 psi (51 MPa) |
| Stiffness (MOE) | 720,000 psi (5 GPa) | 860,000 psi (5.9 GPa) |
| Crushing strength (compression parallel to grain) | 2,570 psi (18 MPa) | 3,930 psi (27 MPa) |
| Shear parallel to grain | 660 psi (5 MPa) | 990 psi (7 MPa) |
A dash means the Handbook prints no value; none is filled in.
Dust and health
- Wood dust is classed as carcinogenic to humans (Group 1) by the International Agency for Research on Cancer, chiefly for cancers of the nose and sinuses.
- NIOSH recommends keeping wood dust exposure to 1 mg/m³ of total dust, as quoted in OSHA's sawmill guidance.
- Germany's federal list of sensitizing substances (TRGS 907) names Triplochiton scleroxylon as a sensitizer of the airways and the skin.
This is what the named authorities publish, not medical advice.
Compare with
Why these numbers
Why these numbers?
The situation
The Wood Handbook prints 430 lbf of side hardness at 12% moisture content for obeche, a value it says was collected from the world literature (Table 5-5b, p. 5-23).
One source: USDA Forest Products Laboratory, collected from the world literature (its Tables 5-5 and 4-4) , sources [1]
What that means
Side hardness (Janka) is the load needed to press a 0.444 in (11.28 mm) steel ball halfway into the wood across the grain; a higher number dents less (Handbook p. 5-5).
One source: USDA Forest Products Laboratory, collected from the world literature (its Tables 5-5 and 4-4) , sources [1]
So
The Handbook gives only the green specific gravity (0.30) for obeche, so it is moved to 12% with the volumetric shrinkage of 9.2% (Eqs. 4-9 and 4-11), then multiplied by water's density and 1.12 (Eq. 4-14).
Arithmetic: exact by definition , sources [1]
The number
About 22 lb/ft³, or 1.9 lb per board foot (1/12 ft³), at 12% moisture content.
Arithmetic: exact by definition
Sources