The Janka Scale for our hardwood species
- Andiroba 1,220 lbf (5,430 N)
- Taurai 1650 lbf (7339.56 N)
- Garapa 1700 lbf (20,040 N)
- TataJuba 1,720 lbf (7,650 N)
- Cambara 1,730 lbf (7,562 N)
- Tigerwood 2,160 lbf (17,500 N)
- Cuban Laurel 2,340 lbf (10,390 N)
- Jatoba 2,350 lbf (25,100 N)
- BloodWood 2,900 lbf (12,900 N)
- Itauba 2,900 lbf (12,900 N)
- Angelim Pedra 3040 lbf (17,600 N)
- Angelim Vermelho 3,160 lbf (14,050 N)
- Massaranduba 3190 lbf (29,290 N)
- Cumaru 3540 lbf (25,580 N)
- Ipe 3680 lbf (25,860 N)
How hard is wood ?
How is it determined ?
What does the test consist of ?
These are just a few questions that might come up when you hear about how hard a wood is.
The fact is not many people understand the testing, and even fewer look to improve upon it. The Janka Scale has done a good job in giving a broad reference to relative hardness. The thing it has solved is some of the issue’s that have evolved from it.
Here’s how the Janka test works:
- A small steel ball 11.28mm (.444 in) is placed on a board.
- Pressure is then applied to the ball until it sinks half of its width into the piece of wood.
- When the ball reaches the halfway point the test is completed and the results recorded.
- For consistency reasons the test is conducted on a flat grain instead of the sides or ends.
Problems With the Janka Test ?
As good as the Janka test is for a “general idea” it does have some issues. Anyone who spends a lot of time around hardwood knows how much grain can vary. The variance in that grain changes the hardness. A small steel ball only tells one small story, about one small part, of one small piece of wood. Within a single piece of decking it is conceivable that there could be several different strengths. Another problem is wood have a hard section (autumnal growth) of grain and a softer (spring growth) section in which the piece isn’t being tested as a whole unit.