Wood species
Kempas wood
Kempas is a hardwood (Koompassia malaccensis). At 12% moisture content it has a Janka hardness of 1,710 lbf (7,606 N) and it weighs about 54 lb/ft³ (871 kg/m³), 4.5 lb (2.06 kg) per board foot.
Key numbers
- Janka hardness, 12% MC
- 1,710 lbf (7,606 N)
- Green: 1,480 lbf (6,583 N)
- Weight at 12% MC
- 54 lb/ft³ (871 kg/m³)
- 4.5 lb per board foot
- Specific gravity (oven-dry weight)
- 0.71 on green volume
- Shrinkage, green to oven-dry
- 7.4% tangential
- Radial 6.0%, volumetric 14.5%
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; kempas's density is worked from its specific gravity with the Handbook's own equations.
How much kempas moves
A 12 in wide flatsawn board of kempas that goes from 6% to 12% moisture content swells about 0.19 in (about 3/16 in, 4.8 mm). Quartersawn, the same board moves about 0.15 in (about 5/32 in, 3.8 mm). Flatsawn faces move 1.2 times as much as quartersawn ones, because the wood shrinks 7.4% around the growth rings but only 6.0% 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
- Brick red when cut, darkening to orange-red or red-brown with many yellow-brown streaks.
- Grain and texture
- Rather coarse texture, typically interlocked grain.
- Working and character
- Hard and heavy, difficult to work by hand or machine. Dries well with some warping and checking; resists decay but not termites.
- Uses
- Heavy construction, railroad ties and flooring.
Adapted in our own words from the Wood Handbook, Chapter 2, p. 2-27.
Strength
Bending strength is the modulus of rupture (MOR); stiffness is the modulus of elasticity (MOE). Values for kempas 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) | 14,500 psi (100 MPa) | 17,700 psi (122 MPa) |
| Stiffness (MOE) | 2,410,000 psi (16.6 GPa) | 2,690,000 psi (18.5 GPa) |
| Crushing strength (compression parallel to grain) | 7,930 psi (55 MPa) | 9,520 psi (66 MPa) |
| Shear parallel to grain | 1,460 psi (10 MPa) | 1,790 psi (12 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 1,710 lbf of side hardness at 12% moisture content for kempas, 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 (0.71) for kempas, so it is moved to 12% with the volumetric shrinkage of 14.5% (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 54 lb/ft³, or 4.5 lb per board foot (1/12 ft³), at 12% moisture content.
Arithmetic: exact by definition
Sources