Wood species
Walnut wood
Walnut is a hardwood (Juglans nigra). At 12% moisture content it has a Janka hardness of 1,010 lbf (4,493 N) and it weighs about 38 lb/ft³ (616 kg/m³), 3.2 lb (1.45 kg) per board foot.
Also called: black walnut.
Key numbers
- Janka hardness, 12% MC
- 1,010 lbf (4,493 N)
- Green: 900 lbf (4,003 N)
- Weight at 12% MC
- 38 lb/ft³ (616 kg/m³)
- 3.2 lb per board foot
- Specific gravity (oven-dry weight)
- 0.55 at 12% MC volume
- 0.51 on green volume
- Shrinkage, green to oven-dry
- 7.8% tangential
- Radial 5.5%, volumetric 12.8%
One source: USDA Forest Products Laboratory, the authority for species properties it measured
Why: Measured by the USDA Forest Products Laboratory; walnut's density is worked from its specific gravity with the Handbook's own equation.
How much walnut moves
A 12 in wide flatsawn board of black walnut that goes from 6% to 12% moisture content swells about 0.2 in (about 3/16 in, 5 mm). Quartersawn, the same board moves about 0.14 in (about 1/8 in, 3.5 mm). Flatsawn faces move 1.4 times as much as quartersawn ones, because the wood shrinks 7.8% around the growth rings but only 5.5% across them.
Worked with the Wood Handbook's dimensional change coefficients for black walnut (Table 13-5: 0.00274 tangential, 0.0019 radial per 1% change in moisture content), which hold between 6% and 14%. 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 brown heartwood; nearly white sapwood up to 3 in. wide in open-grown trees.
- Grain and texture
- Normally straight, with an interesting figure.
- Working and character
- Heavy, hard, strong and stiff with good shock resistance; easy to work, stable in use and well suited to natural finishes.
- Uses
- Furniture, architectural woodwork, decorative panels, gunstocks, cabinets and interior woodwork.
Adapted in our own words from the Wood Handbook, Chapter 2, p. 2-10.
Strength
Bending strength is the modulus of rupture (MOR); stiffness is the modulus of elasticity (MOE). Clear, straight-grained samples of black walnut tested by the Forest Products Laboratory (Wood Handbook Table 5-3b). Knots and cross grain make lumber weaker than these clear samples (Handbook Chapter 5).
| Property | Green | 12% MC |
|---|---|---|
| Bending strength (MOR) | 9,500 psi (66 MPa) | 14,600 psi (101 MPa) |
| Stiffness (MOE) | 1,420,000 psi (9.8 GPa) | 1,680,000 psi (11.6 GPa) |
| Crushing strength (compression parallel to grain) | 4,300 psi (30 MPa) | 7,580 psi (52 MPa) |
| Compression perpendicular to grain | 490 psi (3 MPa) | 1,010 psi (7 MPa) |
| Shear parallel to grain | 1,220 psi (8 MPa) | 1,370 psi (9 MPa) |
| Tension perpendicular to grain | 570 psi (4 MPa) | 690 psi (5 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 USDA Forest Products Laboratory measured black walnut at 1,010 lbf of side hardness at 12% moisture content, on clear, straight-grained samples (Wood Handbook Table 5-3b).
One source: USDA Forest Products Laboratory, the authority for species properties it measured , 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, the authority for species properties it measured , sources [1]
So
Density at 12% is water's density × specific gravity × (1 + 0.12) (Handbook Eq. 4-14): 62.43 × 0.55 × 1.12.
Arithmetic: exact by definition , sources [1]
The number
About 38 lb/ft³, or 3.2 lb per board foot (1/12 ft³), at 12% moisture content.
Arithmetic: exact by definition
Sources