Thread: Specific Gravity - list of Aussie species?

Originally Posted by FenceFurniture

I tell you what - this process has highlighted just how bloody useless common names are (IanW would be having a fit!). Have a look at the Wattles section - There are 3 Black Wattles - all different spp, then there is Early Black Wattle, Early-Flowering BW, Northern BW (ok, reasonable) and I'll bet there are a whole bunch more. Two Purple Gidgees too.

Brett
Did you note that there are three (yes THREE) timbers marketed as "padauk" all with different SG settings 0.57, 0.71, 0.79, though the last two belong to the same species.

Originally Posted by ian

Brett
Did you note that there are three (yes THREE) timbers marketed as "padauk" all with different SG settings 0.57, 0.71, 0.79, though the last two belong to the same species.

Yes I did. I think I saw about 7 Aussie timbers in the Wagner list, and all of them had different SGs to your source material (some significantly different).

Originally Posted by BobL

Have you seen this.
http://www.tocact.org.au/wp-content/...properties.pdf

Thanks for this Bob - very useful. Added 33 species to Ian's list from Wood Database.

Bushmiller has also emailed me an extensive list to sort through - thanks Paul!

It brings up a discussion point though - some of the SGs in that list are quite different to the same species in the Wood Database list. Given that the whole moisture measuring thing is reasonably vague anyway (10-15% is in usable range), at what point should disparities become problematic?

I'm assuming (possibly incorrectly) that moisture measuring is mathematically lineal, and that a difference of 10% in SG will make a difference of 10% in the moisture measurement reading -
i.e. timber with 0.9 SG would read 10% MC different to timber with 1.0 SG, so where one would read 12% MC the other would read 13.2% (without recalibrating the meter) which is not significantly different for these purposes.

That would mean that anything up to ±0.25 difference in SG will make ±2.5% to the MC reading - that should still be more or less in range shouldn't it? A ±0.25 difference in SG would certainly cover all the anomalies that I have come across so far. (I think the biggest was 0.16)


BTW, something I haven't made clear about this meter - and which may be very different to other pinless meters - there is a calibration factor built into it - you enter the SG of the timber into the meter and then take a reading which means there is no need to do a conversion of the reading afterwards.

Originally Posted by FenceFurniture

Thanks for this Bob - very useful. Added 33 species to Ian's list from Wood Database.

Bushmiller has also emailed me an extensive list to sort through - thanks Paul!

It brings up a discussion point though - some of the SGs in that list are quite different to the same species in the Wood Database list. Given that the whole moisture measuring thing is reasonably vague anyway (10-15% is in usable range), at what point should disparities become problematic?

I'm assuming (possibly incorrectly) that moisture measuring is mathematically lineal, and that a difference of 10% in SG will make a difference of 10% in the moisture measurement reading -
i.e. timber with 0.9 SG would read 10% MC different to timber with 1.0 SG, so where one would read 12% MC the other would read 13.2% (without recalibrating the meter) which is not significantly different for these purposes.

That would mean that anything up to ±0.25 difference in SG will make ±2.5% to the MC reading - that should still be more or less in range shouldn't it? A ±0.25 difference in SG would certainly cover all the anomalies that I have come across so far. (I think the biggest was 0.16)

OK, so now we are getting serious

From the adjustment information that accompanies another of Wagner's moisture meters

Commentary on Species Adjustment Tables

In 1992, a study was conducted at the Forest Research Laboratory of Oregon State University on species correction for the Wagner Hand-Held Moisture Meters. The species tested were Douglas Fir, Lodgepole Pine, Western Red Cedar, Western Hemlock, White Fir, Western Larch, Engelmann Spruce, and White Oak. Three to four 40-piece samples of each species were tested. Specific gravity was found to be the primary factor on species adjustment. A species equation as a function of specific gravity and the meter reading was obtained using multiple-regression technique
(R-square = 0.95) as follows:

AF = 8.77 + (0.25 * MM) - (15.86 * SG) - (0.62 * SG * MM)

in which:
AF = Adjustment Factor
MM = Meter Reading
SG = Species average Specific Gravity in oven dry weight and 12% moisture-content volume basis.

The species adjustments provide the adjusted moisture measurements that are based on the species adjustment determined using the species adjustment equation, with rounding to the nearest 0.5

Wood is not a uniform material. Specific gravity of solid-sawn lumber varies within the piece and among pieces. In the OSU study, the average specific gravity for each species differed from the individual sample by plus or minus 1% to plus or minus 8%. For general applications, average specific gravity values can be found in the Wood Handbook (USDA Agriculture Handbook No. 72, 1999). Except for one species for which the experimental value is 7% higher, the species’ overall average specific gravity values obtained in the OSU study are comparable with those in the Wood Handbook. The exception may be caused by unknown biases in the sampling scheme. The Wood Handbook values are used in the tables, except for the imported species, unless otherwise noted.

Species adjustment can be determined for lumber sorted, or otherwise known, to have specific gravity different from the species’ average. One example is lumber graded under the Dense rules. If the specific gravity of a lumber sample is known, species adjustment can be determined by the species adjustment equation.

The species adjustment equation provides a way to expand the use of your Wagner HandHeld Moisture Meter for lumber of any species groups having similar species-specific gravity values. One example is Hem-Fir. For a species group, one way to determine the species adjustment is by the use of a weighted average of the individual species’ average specific gravity values. The weighing procedure used in the ASTM D2555 by standing timber volume can be used. Species adjustment is not recommended for any species group having a broad range of species-specific gravity values. There are no recognized limits on species group species adjustment. Species adjustment for species groups should be used with knowledge on the variability on species involved and the affect of it on species adjustment. If the species mix in the lumber production of a species group is controlled or known to have specific gravity different from that used for the species group, a better estimation of species adjustment can be determined using the known specific gravity in the above species correction equation.

I'll post more later

Many of those species sound like they could be similar to Douglas Fir, in that there is a big difference between the soft rings and the hard rings (I just forget the name for it now). Most noticeable in fast growth trees where the rings are not as tight. Presumably there is a difference in the densities of the two types as well.

These numerical values are for a different Wagner moisture meter, but I believe that the table is still useful.

At some stage -- perhaps tomorrow, perhaps much later -- I'll attempt to follow through the comparison formula I posted above.

Originally Posted by ian

These numerical values are for a different Wagner moisture meter, but I believe that the table is still useful.

Ian, don't think there's any need for you to go to any trouble for the meter that I have - there are no conversions necessary to be done.

I have now combined those three sources (Ian's Wood Database, Bob's Forest Industries, Paul's Bootle sheets) into one spreadsheet, attached. Also attached are the two PDFs for my phone, which may be useful to someone. The PDFs are the "abbreviated" versions: Common name, Botanical name, SG @ 12%.

I'm sure there are more to be added, but only if they are likely to be come across in Oz. My version of "Probable or possible" may not suit everyone of course.....you are very welcome to manipulate the spreadsheet and print some PDFs.

Bet you didn't realise how difficult this task would be when you started, FF. Just to complicate your task I will throw in a few more issues.

Geographic variation: A prime timber in Tasmania is celery top pine (Phyllocladus asplenifolius) which Bootles ascribes a dry density of 650. That is applicable for CTP harvested almost anywhere except the Southern Forests (behind Geeveston) where the timber has visibly closer grain, is noticably heavier with density above 700 and feels different - it "rings" if hit with a hammer.

Provinence variability: Plantation timbers are almost always significantly lighter than bush-grown timber, although standard references almost never mention this factor. I will illustrate this by reference to Tasmanian bluegum (E globulus) and by using hardness janka as a proxy for density as I do not have the latter figures:

• Old growth - janka 12,
• Re-growth - 10.5,
• Plantation - 7 - 7.5.

Never tested: A much loved craft timber in Tasmania is horizontal (Anodopetalum biglandulosum). After 20+ years of searching without results I must conclude that no one has ever actually measured its specification.

The moister meter is not definitive. There are way to many variables for it to be so. I have been using them for as long as they have been available and still find a rap of the knuckle of my index finger on a piece of wood will give a good indication of wet or dry. When supplying timber for the building of the New Parliament House it became evident that not all moister meters were the same or read the same. This caused much delay on the project while an attempt to reach consensus of opinion was undertaken. Indicative would be my approach.

Originally Posted by GraemeCook

Bet you didn't realise how difficult this task would be when you started, FF.

Actually I was aware of the inexact science involved, and all the vagaries of regional difference, plantation differences etc. I also knew I was going to massage whatever it was that came up.

Originally Posted by FenceFurniture

It brings up a discussion point though - some of the SGs in that list are quite different to the same species in the Wood Database list. Given that the whole moisture measuring thing is reasonably vague anyway (10-15% is in the usable range), at what point should disparities become problematic?

I'm assuming (possibly incorrectly) that moisture measuring is mathematically lineal, and that a difference of 10% in SG will make a difference of 10% in the moisture measurement reading - i.e. timber with 0.9 SG would read 10% MC different to timber with 1.0 SG, so where one would read 12% MC the other would read 13.2% (without recalibrating the meter) which is not significantly different for these purposes.

That would mean that anything up to ±0.25 difference in SG will make ±2.5% to the MC reading - that should still be more or less in range shouldn't it? A ±0.25 difference in SG would certainly cover all the anomalies that I have come across so far. (I think the biggest was 0.16)

In the absence of comments on my theory in post #34 I'll have to assume it is reasonable logic.

Brett

I don't have all my data to hand at the moment, but my initial comment would be to look at the moisture correction tables I sent to you. While I appreciate your meter relies on the density of the timber (albeit expressed as SG, which I find unusual in itself) and does not require correction tables, you will note that the corrections themselves are not linear. Neither do timbers of similar densities have the same correction factor.

All I would say without delving deeply into the figures is that an indicated MC of 12% will probably be around 10% to 15% for any timber (that is a wild guess as it could be 8% to 20%) and the real question is whether that is suitable for the area where you live. If timber is dried down below the equilibrium MC it will rebsorb moisture to the humidty conditons of where you live, although this may take a few weeks to happen. In times gone by, floorbords were only temporarily layed down for this reason and then permanently fixed some weeks later.

One shortcoming I see with your meter (of which I am completely unfamiliar ) is that you need to know what timber you are measuring and know the density or be able to accurately weigh a sample piece to ascertain the density, although when I think on it all meters have an inherent failing in this regard.

I believe the only truly accurate way of meauring MC is the oven dry method, but perhaps others closely connected with the industry can comment.

Regards
Paul

Paul, as I understand it (wrt timber), Specific Gravity = Density at 12%MC so the SG for a piece of timber at any MC is still xx, whereas the density is whatever it is at the current MC. I may well be confused though. In other words the SG is the baseline for each species to work from.

Following on from that I would have thought that the correction tables issued with meters will do the same correction as changed the SG within my meter.

For the oven dry method: I don't know exactly how it works but it sounds like a sample piece is put in an oven at about 100° until it stops losing weight, and then use the weights before and after drying to work out the MC?

The test should be conducted at 103C with a variable of plus or minus 2C.