Wood species
Keruing wood
Keruing is a hardwood (Dipterocarpus spp.). At 12% moisture content it has a Janka hardness of 1,270 lbf (5,649 N) and it weighs about 53 lb/ft³ (855 kg/m³), 4.5 lb (2.02 kg) per board foot.
Also called: apitong, yang.
Key numbers
- Janka hardness, 12% MC
- 1,270 lbf (5,649 N)
- Green: 1,060 lbf (4,715 N)
- Weight at 12% MC
- 53 lb/ft³ (855 kg/m³)
- 4.5 lb per board foot
- Specific gravity (oven-dry weight)
- 0.69 on green volume
- Shrinkage, green to oven-dry
- 10.9% tangential
- Radial 5.2%, volumetric 16.1%
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; keruing's density is worked from its specific gravity with the Handbook's own equations.
How much keruing moves
A 12 in wide flatsawn board of keruing that goes from 6% to 12% moisture content swells about 0.29 in (about 9/32 in, 7.3 mm). Quartersawn, the same board moves about 0.13 in (about 1/8 in, 3.3 mm). Flatsawn faces move 2.1 times as much as quartersawn ones, because the wood shrinks 10.9% around the growth rings but only 5.2% 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
- Light to dark red-brown or brown, sometimes purplish; gray or buff sapwood.
- Grain and texture
- Moderately coarse texture, straight or shallowly interlocked grain, with resin ducts.
- Working and character
- Strong, hard and heavy. Easy to saw and machine, especially green, but silica dulls cutters and resin sticks to tools and can upset gluing and finishing.
- Uses
- General construction, boat framing, flooring, truck floors, pallets, plywood and boardwalks.
The Handbook reports that most keruing species are rated endangered or critically endangered by the IUCN.
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 keruing 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) | 11,900 psi (82 MPa) | 19,900 psi (137 MPa) |
| Stiffness (MOE) | 1,710,000 psi (11.8 GPa) | 2,070,000 psi (14.3 GPa) |
| Crushing strength (compression parallel to grain) | 5,680 psi (39 MPa) | 10,500 psi (72 MPa) |
| Shear parallel to grain | 1,170 psi (8 MPa) | 2,070 psi (14 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 1,270 lbf of side hardness at 12% moisture content for keruing, 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 (0.69) for keruing, so it is moved to 12% with the volumetric shrinkage of 16.1% (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 53 lb/ft³, or 4.5 lb per board foot (1/12 ft³), at 12% moisture content.
Arithmetic: exact by definition
Sources