Wood species
Okoume wood
Okoume is a hardwood (Aucoumea klaineana). At 12% moisture content it has a Janka hardness of 380 lbf (1,690 N) and it weighs about 25 lb/ft³ (396 kg/m³), 2.1 lb (0.94 kg) per board foot.
Key numbers
- Janka hardness, 12% MC
- 380 lbf (1,690 N)
- Weight at 12% MC
- 25 lb/ft³ (396 kg/m³)
- 2.1 lb per board foot
- Specific gravity (oven-dry weight)
- 0.33 on green volume
- Shrinkage, green to oven-dry
- 6.1% tangential
- Radial 4.1%, volumetric 11.3%
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; okoume's density is worked from its specific gravity with the Handbook's own equations.
How much okoume moves
A 12 in wide flatsawn board of okoume that goes from 6% to 12% moisture content swells about 0.15 in (about 5/32 in, 3.9 mm). Quartersawn, the same board moves about 0.1 in (about 3/32 in, 2.6 mm). Flatsawn faces move 1.5 times as much as quartersawn ones, because the wood shrinks 6.1% around the growth rings but only 4.1% 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
- Salmon-pink heartwood with narrow whitish or pale gray sapwood.
- Grain and texture
- High luster and uniform texture, a little coarser than birch.
- Working and character
- Dries readily but is not durable. Silica makes sawn lumber somewhat hard to machine; it glues, nails and peels for veneer easily, and its medium color can be toned lighter or darker.
- Uses
- Decorative and utility plywood, doors, furniture parts and joinery.
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 okoume from Wood Handbook Table 5-5b (p. 5-24), 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) | — | 7,400 psi (51 MPa) |
| Stiffness (MOE) | — | 1,140,000 psi (7.9 GPa) |
| Crushing strength (compression parallel to grain) | — | 3,970 psi (27 MPa) |
| Shear parallel to grain | — | 970 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.
This is what the named authorities publish, not medical advice.
Compare with
Why these numbers
Why these numbers?
The situation
The Wood Handbook prints 380 lbf of side hardness at 12% moisture content for okoume, a value it says was collected from the world literature (Table 5-5b, p. 5-24).
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 (0.33) for okoume, so it is moved to 12% with the volumetric shrinkage of 11.3% (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 25 lb/ft³, or 2.1 lb per board foot (1/12 ft³), at 12% moisture content.
Arithmetic: exact by definition
Sources