Measuring wood density

[RyanY]

Anyone still measure wood density? I used to do this more often with off cuts from longer boards before I would mark them out. This time I made four 10”x0.75”x0.75” pieces from scrap that were cut out from the board I’m using. I dried it at 200-225 for several hours in the oven. Seemed to only be losing a tenth of a gram or less over the last 2 hours. I microwaved it for good measure at the end and didn’t get any measurable change in mass. My calculations using just mass/volume are giving me SG’s of over 0.8 in this board. Seems heavy for red oak. Even with a 10% margin of error that would be 0.72. Thoughts?

[Yooper Bowyer]

It could be that dense, what are the final dimensions in mm and mass in grams?

[RyanY]

All were cut to the same dimensions adding up to around 92.2cm3. The four masses were 76.9, 81.3, 77.5, and 69.7 grams. I got an average SG of 0.818.

[Eric Garza]

Was the board treated, or raw lumber?

[RyanY]

From a big box store so I assume kiln dried.

[PatM]

Do the water flotation  test.

[RyanY]

Good idea Pat. I did the float test and it seemed to correlate to the numbers I had. Here’s a piece that was about 8.25” under for a 10” long piece. They correlated to the same measurements I made by volume and mass with regard to the lightest floating the most. Seems like this piece of oak may be as dense as some Osage. I’ll have to re think the measurements of my design.

[Yooper Bowyer]

Would a bent test help first?  Also, the mass principal is a well accepted guide for making bows out of such wood anomalies.

[PatM]

This  is a scenario where you hope the increased density is meaningful in an elasticity increase as well.

  I've seen other references to Red Oak  being denser than average.  Not an uncommon trait for wood in general.

[RyanY]

I should learn how to do a bend test. I was mainly curious about other's still testing density. I think I'll be able to take the width on this one down a bit as a result of the density.

Pat, even if elasticity is the same with a more dense piece, does this mean it would bend to the same degree as less dense wood and just take more force to do so? That is my assumption. I was looking up a few terms last night with regard to these properties like MOR, MOE, etc. Interestingly, osage and red oak have similar MOE numbers.

[PatM]

I believe  that would be correct.

[willie]

Interestingly, osage and red oak have similar MOE numbers.

in spite of its name, MOE, (modulus of elasticity) is how much force to bend.  Elasticity, as we as bowyers use the term, is not usually quantified in wood tests as a property found in the tables.

I measure density, although at "bow dry" moisture levels. and also measure stiffness with a simple bend test, and while i am at it just go ahead and take one more measurement to find the point of set taking.

[RyanY]

Interestingly, osage and red oak have similar MOE numbers.

in spite of its name, MOE, (modulus of elasticity) is how much force to bend.  Elasticity, as we as bowyers use the term, is not usually quantified in wood tests as a property found in the tables.

I measure density, although at "bow dry" moisture levels. and also measure stiffness with a simple bend test, and while i am at it just go ahead and take one more measurement to find the point of set taking.

Willie, I’d be interested in hearing more about how you do those tests. Might as well use the scrap I have for something!

[willie]

I rip arrow stock on a table saw and find it easy to test square stock for MOE on a setup like a spine tester if you can measure thickness fairly close.
when testing for set I use a bow scale and some blocks clamped to the edge of the workbench.

The caliper will get you by for all measurements,  but I also have a cheapo dial indicator to make the deflection measurements easier. Calipers are actually designed to measure thicknesses of round stock while a micrometer is designed for flat stuff. The jaw spread of the caliper makes it a useful tool for a lot of things around the shop, and would be the minimal required tool if you were limited budget wise.

[Jim Davis]

I was looking up a few terms last night with regard to these properties like MOR, MOE, etc. Interestingly, osage and red oak have similar MOE numbers.

All those MOE, MOR, etc were established by the Forest Products Laboratories back in the 1920s. They are good numbers (mostly*)and have been republished by some websters who present them as if they're new and their own.

*The problem we encounter is that FPL's data includes nothing for dried Osage. If you look at FPL's own data, you will see that their test results are only shown for green Osage. Those numbers are similar to red oak, but they are NOT what dry Osage would show. I have berated and badgered FPL many times trying to get them to finish the job, but usually do not even get a response.

FPL https://www.fpl.fs.fed.us/documnts/TechSheets/HardwoodNA/htmlDocs/maclura.html

willie, I never heard that tool distinction in my 10 years working in production machine shops and have never had a problem measuring flat or round stock with either tool.