Wood species
Purpleheart wood
Purpleheart is a hardwood (Peltogyne spp.). At 12% moisture content it has a Janka hardness of 1,860 lbf (8,274 N) and it weighs about 50 lb/ft³ (798 kg/m³), 4.2 lb (1.88 kg) per board foot.
Also called: amaranth.
Key numbers
- Janka hardness, 12% MC
- 1,860 lbf (8,274 N)
- Green: 1,810 lbf (8,051 N)
- Weight at 12% MC
- 50 lb/ft³ (798 kg/m³)
- 4.2 lb per board foot
- Specific gravity (oven-dry weight)
- 0.67 on green volume
- Shrinkage, green to oven-dry
- 6.1% tangential
- Radial 3.2%, volumetric 9.9%
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; purpleheart's density is worked from its specific gravity with the Handbook's own equations.
How much purpleheart moves
A 12 in wide flatsawn board of purpleheart that goes from 6% to 12% moisture content swells about 0.15 in (about 5/32 in, 3.9 mm). Quartersawn, the same board moves about 0.08 in (about 3/32 in, 2 mm). Flatsawn faces move 1.9 times as much as quartersawn ones, because the wood shrinks 6.1% around the growth rings but only 3.2% 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
- Brown when cut, turning deep purple in air and eventually dark brown in light.
- Grain and texture
- Medium to fine texture, usually straight grain.
- Working and character
- Strong and heavy, moderately hard to work, and it dulls cutters quickly; dull tools heat it and draw out gummy resin, so the Handbook suggests a slow feed and hardened cutters. Turns easily, glues and finishes well; highly resistant to decay.
- Uses
- Turnery, marquetry, cabinets, fine furniture, parquet, cue butts and carvings; also heavy construction.
Adapted in our own words from the Wood Handbook, Chapter 2, p. 2-34.
Strength
Bending strength is the modulus of rupture (MOR); stiffness is the modulus of elasticity (MOE). Values for purpleheart from Wood Handbook Table 5-5b (p. 5-24), 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) | 13,700 psi (94 MPa) | 19,200 psi (132 MPa) |
| Stiffness (MOE) | 2,000,000 psi (13.8 GPa) | 2,270,000 psi (15.7 GPa) |
| Crushing strength (compression parallel to grain) | 7,020 psi (48 MPa) | 10,320 psi (71 MPa) |
| Shear parallel to grain | 1,640 psi (11 MPa) | 2,220 psi (15 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 1,860 lbf of side hardness at 12% moisture content for purpleheart, a value it says was collected from the world literature (Table 5-5b, p. 5-24).
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 (0.67) for purpleheart, so it is moved to 12% with the volumetric shrinkage of 9.9% (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 50 lb/ft³, or 4.2 lb per board foot (1/12 ft³), at 12% moisture content.
Arithmetic: exact by definition
Sources