Dry Lumber Weight Versus Green

[Camp]

A quick question from a newbie.

I love the toolbox for figuring things on here, but wanted to know, is there somewhere on here or elsewhere that can give the approximate weight on drier lumber? The toolbox has weights based on green only (unless I missed part of it).

Specifically, I have about 1,500' of yellow poplar logs, that were given to me, that I plan to have milled on site soon. They were cut late last summer and appear to still be solid and useable.  I will need to haul the lumber and am just trying to decide exactly what size trailer, etc. I will need to handle the weight.

Green weight comes out to about 4,800 but I know these will be quite a bit less due to drying for about 9 months. And I do reailze that aren't considered completly dry but I'm hoping they will be light enough to haul the sawed wood on an F-150 and a small single axle hitch trailer. (since I don't have a gooseneck)

Thanks

[LeeB]

You can still figure it being pretty close to the green weight. It doesn't dry out very quickly while still in the log.

[Camp]

Thanks

[SwampDonkey]

Method1: One sure fire way is to weigh some samples in the pile, maybe cut off some cookies from some junk logs and weigh them, find their cubic volume in feet, average their weight per ft³, and then find volume of the load with Huber's volume equation.

Huber's= length x diameter² x 3.14  *take diameter mid way up the log
                              4

Method 2: With the empirical method, I can only give you a ball park figure for different MC% and not factoring in the bark, just the wood. These are based on empirical data and formulas which is based on oven dry weight, partial shrinkage from drying and green specific gravity. And this assumes the wood is dried evenly, which it won't be, so assume a little heavier from more moisture.

specific gravity of yellow poplar when green (Gg) is 0.40, fibre saturation point (FSP) assumed to be 30% MC.
Density of water (Dw) is 62.4 lb/ft³ @ 40-70° F, volumetric shrinkage from green to oven  dry (Vsh%) is 12.7 %  *** these figures are in the Wood Handbook from USDA.

Calculate:
Weight oven dried = 0.40 x 62.4 lb/ft³X1ft³ = 24.96 lbs

Partial volumetric shrinkage is:

@26% = 12.7% x (30-26) = 1.69 %
               30 %
specific gravity @ 26% is:
=           Gg                 =     0.40     = 0.407 = G₂₆
    1- partial shrinkage        1-1.69
                 100                   100

G₂₆x Dw = 0.407x62.4 = 25.4 lb/ft³ of OD wood
Weight of wood in 26% condition:
W₂₈=Wo + 26/100 x Wo
    = 25.4 + (0.26 x 25.4) = 32 lbs/ft³

for MC of 20% it works out to 31.26 lb/ft³ of solid wood

Now find volume of your load and multiply the numbers.

Wood Handbook list G_12% = 0.42 and W_12% = 30 lbs/ft³ for comparisons.

The biggest loss of moisture seems to be from green to air dried, then not much after 26%. Green in the Wood Handbook is 46 lbs/ft³. I would use green weight to be safe as you don't know the actual MC. Heartwood in poplar is around 83 % MC when green, meaning 83% of the weight is water versus oven dry wood. Basically, the weight of water in a green poplar log fresh cut is around 20-22 lbs. So you see  it's a crap shoot when the MC is not known in your logs when using this math. Volume doesn't change above FSP, but weight does because of water. This math is more practical when looking at dimensional shrinkage in lumber and actual volume of wood pulp.

[DouginUtah]

Bill, help me out here. What is the name of the guy who wrote what are probably the two most popular and comprehensive books on wood (for woodworkers)?

He lists yellow-poplar at 10 12% M.C. as 26 lbs./cf.

Edit: I mistakenly wrote 10%. It should have been 12%.

[metalspinner]

Hoadley.

[SwampDonkey]

Doug the trouble with the math I used, as I later pointed out is fresh cut green wood has a lot of moisture and is well above the fibre saturation point. Most of the math is for finding dimensional change which occurs below the fibre saturation point and actual wood substance recoverable in given wood volume. Volume as we know does not change above the FSP. So besides scaling a load of fresh pulp by weight for instance, moisture above the FSP has no bearing on what I'm buying for wood volume. When I start drying the stuff below FSP then it matters a whole lot more. My lumber looses volume, and I'm only interest in dry pulp volume as that's what's wrapped at the end of the process in them round bales.  ;)

Where is your source Doug for the 26 lb/ft3 at 10%? I have two sources here (Wood Handbook and Wood Tech) that says 30 lb/ft³ at 12 %. Weight loss is relative to water loss which is 62.4 lb/ft³. The difference is probably in the fibre saturation point Doug. The assumption is usually 30% but maybe he has used a closer figure.

Weight oven dried = Specific gravity green X density of water X green volume.
Since we are talking in green condition, just use 1 ft³ for the volume.

[SwampDonkey]

Here is a clipping.

[SwampDonkey]

Here is a "theoretical shrinkage schematic" from Dr. Sebastian's Wood Science lab notes.

[Magicman]

Camp, now that you are getting your head full of numbers......Welcome to The Forestry Forum......

[DouginUtah]

Metalspinner got it; R.Bruce Hoadley. I'm not sure which book the 12% weight came from--either Understanding Wood or Identifying Wood.

I got the number (today) from the program I wrote: Timber, which is a download on my website. (Highlight the weight slider and press F1 for the complete list of species weights at 12%. Note: do not change the Form Class Slider--there is an error.)

[SwampDonkey]

Doug, I don't see where you would select a species in there. I see a number beside the weight/CF fields, but no table of weights @12% by species.  :  You drying down to 12 %? Maybe 16 or 20. ;)

I couldn't open the file in MS Access 2000's VB editor.

[SwampDonkey]

I think we scared him off, but weighing the samples is the best way for this application.

Welcome Camp.  ;D

[LeeB]

I think if he has logs that have been down 9 months, the weight won't have changed enough to vary a whole lot from what the calculator here on the forum gave him. Being as he was trying to size a trailer for hauling the lumber, I would think it best to opt for more anyway.

[Camp]

Naaaaaaaaahhhhhhhh! I didn't get scared off.

I just spent the last 2 days "auditing" a calculus class at the local community college so I could come back and figure out what y'all were saying!  ;D

Glad I was in math honors.

Honestly, I've just been busy and am checking back in. Thanks for all the input. Believe it or not.......some of it made sense to me! 

Sounds like a crap shoot anyway to figure mathematically by guessing the water weight with the variables involved.

I'll just weight up some and calculate or just see if I can borrow a bigger trailer from somebody!   ;)

[DouginUtah]

I see a number beside the weight/CF fields, but no table of weights @12% by species. 

If you see the weight/C.F. slider then you have the program running. Click on the arrow to change the number. Then press F1. The complete list will display in the upper right of the window. Click on the species whose weight you want then press calculate.

[SwampDonkey]

Doug, those values look to be at 6% MC.

[DouginUtah]

Maybe we could get someone who has the book to look up the numbers and post whether they are for 12% or not.

Afrormosia 39
Alder, grey 29
Alder red 26
Alder 25
Apple 39
Ash, black 31
Ash, European 38
etc.

[SwampDonkey]

I have the Wood Hand Book and the Textbook of Wood Technology. At 12 %, all the figures are higher than those. ;D Some species are not tabulated in my Textbook table, but I think those are in the Wood Handbook. They just don't organize the data the same. But they always list green and 12%. The Wood Handbook will occasionally list other moister %'s, but not consistently for all species.

The Wood Handbook is a free download from the USDA.

Western red cedar @ 9% has a sp. gr. of 0.33 in the Handbook
                          @ 12%                    0.32  23lb/ft³
                           green                     0.31   27lb/ft³

I checked the tabulated figures in those texts with the math to go from one MC to another and it jives. They round figures up. For instance @12% I calculate 22.57 lb/ft³. I did the math for 9% MC and get 22.1 lb/ft³, they would round down to 22. With sp. gravity of 0.325, they round up to 0.33.

[Dave Shepard]

Hoadley lists specific gravity at 12% MC in "Identifying Wood". I don't see a weight per pound anywhere. I could get the other book out and look, it's around here, somewhere.