Wood species
Cativo wood
Cativo is a hardwood (Prioria copaifera). At 12% moisture content it has a Janka hardness of 630 lbf (2,802 N) and it weighs about 30 lb/ft³ (473 kg/m³), 2.5 lb (1.12 kg) per board foot.
Key numbers
- Janka hardness, 12% MC
- 630 lbf (2,802 N)
- Green: 440 lbf (1,957 N)
- Weight at 12% MC
- 30 lb/ft³ (473 kg/m³)
- 2.5 lb per board foot
- Specific gravity (oven-dry weight)
- 0.40 on green volume
- Shrinkage, green to oven-dry
- 5.3% tangential
- Radial 2.4%, volumetric 8.9%
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; cativo's density is worked from its specific gravity with the Handbook's own equations.
How much cativo moves
A 12 in wide flatsawn board of cativo that goes from 6% to 12% moisture content swells about 0.13 in (about 1/8 in, 3.4 mm). Quartersawn, the same board moves about 0.06 in (about 1/16 in, 1.5 mm). Flatsawn faces move 2.2 times as much as quartersawn ones, because the wood shrinks 5.3% around the growth rings but only 2.4% 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
- Pale pink or distinctly reddish sapwood, usually wide; small heartwood.
- Grain and texture
- Straight, uniform texture comparable with true mahogany.
- Working and character
- Dries quickly with little degrade and is very stable, nearly equal to mahogany. Not durable. It can hold resin, but properly dried wood finishes without trouble.
- Uses
- Interior woodwork, furniture and cabinet parts, plywood core, picture frames, door edge banding and millwork.
Adapted in our own words from the Wood Handbook, Chapter 2, p. 2-22.
Strength
Bending strength is the modulus of rupture (MOR); stiffness is the modulus of elasticity (MOE). Values for cativo from Wood Handbook Table 5-5b (p. 5-22), 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) | 5,900 psi (41 MPa) | 8,600 psi (59 MPa) |
| Stiffness (MOE) | 940,000 psi (6.5 GPa) | 1,110,000 psi (7.7 GPa) |
| Crushing strength (compression parallel to grain) | 2,460 psi (17 MPa) | 4,290 psi (30 MPa) |
| Shear parallel to grain | 860 psi (6 MPa) | 1,060 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 630 lbf of side hardness at 12% moisture content for cativo, a value it says was collected from the world literature (Table 5-5b, p. 5-22).
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 (0.40) for cativo, so it is moved to 12% with the volumetric shrinkage of 8.9% (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 30 lb/ft³, or 2.5 lb per board foot (1/12 ft³), at 12% moisture content.
Arithmetic: exact by definition
Sources