Wood Density Data and Janka Hardness Estimations

[Isaac Litster]

My preferred type of turning is dry wood. I like hard, dense, fine-grained, and even texture. The harder the wood, the better (usually). I found that Janka hardness is a good measure of this from my reading on The Wood Database. However, there are more species out there than are on the website, and even some that are on the website may be different growing here. I can get old-growth pine, or spruce that is so full of resins that it is denser and harder than any exotic. So, I began to wonder how the Janka hardness would compare to those known values for black cherry, for example. Looking through the wood database, I noticed some species had an icon saying that the Janka hardness was estimated by the specific gravity. I know I can calculate the specific gravity of my own samples, so I can estimate the Janka hardness. I created a function to model the Janka hardness based on the dried weight (in kg/m^3), based on a dataset of about 10 species and their confirmed hardness. The function is linear, which turns out to be different from the function that was linked from the USDA. However, I stuck with mine because it had more accurate results, in my opinion. I used a precise scale to weigh my samples and calipers to calculate the volume of my samples. The samples are all spheres and cubes that I made out of some of the wood I have. This is not super scientific, as the samples are not 100% perfect geometrically, and also may contain knots, cracks, or tiny voids. I avoided large defects, but some of the samples, such as burls and the antler, are not uniform in density throughout. Also, the samples are all relatively small, so the errors are exacerbated. Some interesting observations are that the same species can be radically different between trees. Also, I acknowledge that the hardness is not directly proportional to the density; that is clear, lead is not one of the hardest metals, I know.


I attached a PDF of my data because the post is apparently too long.

 

[John K Jordan]

Interesting project. Are the numbers in the "Confirmed" column from the published data?

There are so many varieties and SO many names- for example, is the Mahogany Honduran?
(http://hobbithouseinc.com/personal/woodpics/_discussion_mahogany.htm)

It would be interesting to try janka hardness testing with hydraulic press with a calibrated pressure gauge - not sure I trust the gauge on my 20-ton press for relatively low pressures like these! Also don't know where to find the "official" size steel ball.

Do you need a piece of flowering Dogwood to test? (one of my favorites to turn, hard, fine-grained.

JKJ

 

[Isaac Litster]

Interesting project. Are the numbers in the "Confirmed" column from the published data?

There are so many varieties and SO many names- for example, is the Mahogany Honduran?
(http://hobbithouseinc.com/personal/woodpics/_discussion_mahogany.htm)

It would be interesting to try janka hardness testing with hydraulic press with a calibrated pressure gauge - not sure I trust the gauge on my 20-ton press for relatively low pressures like these! Also don't know where to find the "official" size steel ball.

Do you need a piece of flowering Dogwood to test? (one of my favorites to turn, hard, fine-grained.

JKJ

The "confirmed" numbers are mostly from the Wood Database, unless I found them elsewhere. The mahogany was odd; it seemed to be very hard. I don't know what species it is; it came from offcuts from a yard in Oregon. I think that is a miscalculation; perhaps the sphere wasn't turned as accurately as the others, or my model was flawed.

I agree that it would be interesting to do a more "official" testing with the press, especially as there are so many varieties. I am interested to know, for example, what the difference in hardness is for some of the local softwoods, such as yellow cedar, Sitka spruce, and hemlock, comparing the new-growth 10 rings/inch to the old-growth ~200 rings/inch.

I would love some dogwood to "test". Do you have some for a test or two?

 

[John K Jordan]

The mahogany was odd; it seemed to be very hard. I don't know what species it is; it came from offcuts from a yard in Oregon.

DId you see the article on mahogany on the Wood Database?

Mahogany Mixups: the Lowdown | The Wood Database

www.wood-database.com

Many dealers just make a guess or use whatever name was given by their source. Examining prepared endgrain with magnification really helps.

I have a variety of wood labeled mahogany. The "true" Honduran I have is softer than some other Swietenia species, for example Cuban. It's certainly less dense than some of the mahogany look-a-likes using the scientific method of picking up a plank. Easy to turn, although I prefer the finished look of Sapele.

JKJ

 

[Mark Jundanian]

Perhaps the location and environment the tree grew in may also be a factor. They can effect appearance, so maybe hardness, too?

 

[robo hippy]

A lot of woods are sold as "mahogany" but at best, most are still trees anyway. I would expect woods, like people to be highly variable. I did have a guy in Australia send me some acacias from the outback that have specific gravity of 1.4. I know they are in my shop somewhere.... Almost to the "sinks like a rock" density. I traded him for some Mountain Mahogany since he was making penny whistles out of woods with specific gravity of 1.0 or more.

robo hippy

 

[Isaac Litster]

Perhaps the location and environment the tree grew in may also be a factor. They can effect appearance, so maybe hardness, too?

100% I have crabapple that is grown partially submerged in the bog in the shade, and some that grew under the powerlines. The wood is nearly unrecognisable. The tree in the bog was very hard, like you would expect from a dense hardwood, while the one under the powerline was powdery, and about as soft as cottonwood. The difference is incredible.