Wood species
Hackberry wood
Hackberry is a hardwood (Celtis occidentalis). At 12% moisture content it has a Janka hardness of 880 lbf (3,914 N) and it weighs about 37 lb/ft³ (594 kg/m³), 3.1 lb (1.4 kg) per board foot.
Also called: sugarberry.
Key numbers
- Janka hardness, 12% MC
- 880 lbf (3,914 N)
- Green: 700 lbf (3,114 N)
- Weight at 12% MC
- 37 lb/ft³ (594 kg/m³)
- 3.1 lb per board foot
- Specific gravity (oven-dry weight)
- 0.53 at 12% MC volume
- 0.49 on green volume
- Shrinkage, green to oven-dry
- 8.9% tangential
- Radial 4.8%, volumetric 13.8%
One source: USDA Forest Products Laboratory, the authority for species properties it measured
Why: Measured by the USDA Forest Products Laboratory; hackberry's density is worked from its specific gravity with the Handbook's own equation.
How much hackberry moves
A 12 in wide flatsawn board of hackberry that goes from 6% to 12% moisture content swells about 0.23 in (about 7/32 in, 5.8 mm). Quartersawn, the same board moves about 0.12 in (about 1/8 in, 3 mm). Flatsawn faces move 1.9 times as much as quartersawn ones, because the wood shrinks 8.9% around the growth rings but only 4.8% across them.
Worked with the Wood Handbook's dimensional change coefficients for hackberry (Table 13-5: 0.00315 tangential, 0.00165 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
- Pale yellow to greenish or grayish yellow sapwood; darker heartwood.
- Grain and texture
- Similar in structure to elm.
- Working and character
- Moderately heavy, moderately to very hard, high in shock resistance but low in stiffness. It shrinks a lot yet keeps its shape well while drying.
- Uses
- Lumber, furniture parts, dimension stock and veneer.
Adapted in our own words from the Wood Handbook, Chapter 2, p. 2-7.
Strength
Bending strength is the modulus of rupture (MOR); stiffness is the modulus of elasticity (MOE). Clear, straight-grained samples of hackberry 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) | 6,500 psi (45 MPa) | 11,000 psi (76 MPa) |
| Stiffness (MOE) | 950,000 psi (6.6 GPa) | 1,190,000 psi (8.2 GPa) |
| Crushing strength (compression parallel to grain) | 2,650 psi (18 MPa) | 5,440 psi (38 MPa) |
| Compression perpendicular to grain | 400 psi (3 MPa) | 890 psi (6 MPa) |
| Shear parallel to grain | 1,070 psi (7 MPa) | 1,590 psi (11 MPa) |
| Tension perpendicular to grain | 630 psi (4 MPa) | 580 psi (4 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 hackberry at 880 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 × 0.53 × 1.12.
Arithmetic: exact by definition , sources [1]
The number
About 37 lb/ft³, or 3.1 lb per board foot (1/12 ft³), at 12% moisture content.
Arithmetic: exact by definition
Sources