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Air dried log weight

Started by knowslittle, September 16, 2010, 07:38:04 PM

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knowslittle

   Does anyone here know where I can get somewhat reliable data on the weights of logs given a specific moisture content?
  The toolbox section here has a table for green logs., but the ones I'm bidding to build 4 trellis' and 3 false ceilings with will have been somewhat air dried.

Even If I had a rough idea of green vs. say 20% or 30% weight, the math would be easy enough to do.
  Or, my guess is I could do it with the given the specific gravity and volume, but I was hoping to make it simpler.

Thank you,
Bob

Jeff

Logs are not typically sold or bought with an expectation of any given internal moisture content.
Just call me the midget doctor.
Forestry Forum Founder and Chief Cook and Bottle Washer.

Commercial circle sawmill sawyer in a past life for 25yrs.
Ezekiel 22:30

SwampDonkey

Are you looking to get weights for transporting the logs? I wouldn't know any other purpose personally. If you do use specific gravity, be sure you use it based on current MC% as the wood handbook only gives it for Green (30 %) and 12 %, you have to calculate it based on partial volumetric shrinkage. Or just use the green figures and estimate high for a safety factor.

You can Google "Wood Handbook" for the figures of NA species. I think the document is around 14.5 MB and the latest issue was 1999. But that data is decades old and still holds it's own, only one mistake is the red pine, where the SP Gr noted for 12 % is actually OD condition, at 12 % it should be 0.44. That error has been known for some time and doesn't seem to get "fixed". I mean before 1999 even. Might be a little hard finding the Volumetric shrinkages in there, doesn't have a concise table like the 4th Ed. Textbook of Wood Technology by Panshin and De Zeeuw (1980).

An example would be hard maple with Vsh% of 14.7% from green to oven dry condition and calculating fibre saturation point from empirical data  and specific gravity (green) is 0.56. Lets air dry to 20 %.

FSP = 26.25  round to 26.3%

partial Vol Shrinkage = 14.7% x (26.3%-20%) = 3.5%
                                 26.3%

spec gravity @20% = 0.56           ~ 0.58 denoted as G20
                              1-3.5%
                                  100

Wood handbook lists hard maple as 0.63 @ 12% for comparison.

lets say we had 50 ft3 of logs using Hubers volume equation
oven dried weight = G20 x V20% x density water (@ 40-70° F)
                           = 0.58 x 50 ft3 x 62.4 lbs/ft3
                           ~1810 lbs
Now, how much at 20 % MC?
W20% = 1810 lbs + 0.20 x 1810 lbs ~ 2172 lbs

[edited with calculated FSP]
"No amount of belief makes something a fact." James Randi

1 Thessalonians 5:21

2020 Polaris Ranger 570 to forward firewood, Husqvarna 555 XT Pro, Stihl FS560 clearing saw and continuously thinning my ground, on the side. Grow them trees. (((o)))

knowslittle

Jeff- I was looking for the weight because as I work alone, I'm trying to find solutions to raising the logs into place within the confines of a room or a 2nd story balcony, Genie lift, Load-all, etc..

Swampdonkey- Excellent!  Thank you much for your trouble and info.   Great help guys.

Thank you, it's a good start.
bob

Jeff

Logs may take many years to dry in the log form if ever. I would think you would want to use the green weight plus a fudge factor for safety's sake.
Just call me the midget doctor.
Forestry Forum Founder and Chief Cook and Bottle Washer.

Commercial circle sawmill sawyer in a past life for 25yrs.
Ezekiel 22:30

Jim_Rogers

Quote from: Jeff on September 17, 2010, 09:41:03 AM
I would think you would want to use the green weight plus a fudge factor for safety's sake.

I totally agree.....
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

knowslittle

Jeff and Jim-  you know, you're absolutely right.  Just a novice using novice-type thinking.
Appreciate it gentlemen.
Bob

SwampDonkey

That's why I also suggested using the green figures in my post. ;)
"No amount of belief makes something a fact." James Randi

1 Thessalonians 5:21

2020 Polaris Ranger 570 to forward firewood, Husqvarna 555 XT Pro, Stihl FS560 clearing saw and continuously thinning my ground, on the side. Grow them trees. (((o)))

knowslittle

Again thanks to all for your help.

  What I was trying to do was determine the weight of logs shipped, de-barked, from about 1200 miles away (Montana). According to the company providing the logs, given they are w/out bark, and will be traveling down the highway (probably uncovered in the wind, perhaps @ 60 MPH), they should (again according to the provider) be at or about 20% MC.

  As this job requires handling by me alone, weight upon delivery is of interest.

Also, I'm not so sure the engineer has calculated the load capabilities for basically green timbers, but thats another issue.

  Sorry, I should have made myself more clear.

Thanks again,
Bob

beenthere

So from Montana, are you buying Lodgepole pine logs?  And are they possibly from dead trees?  There is a house log market from this Lodgepole pine.

The seller may be trying to convince you that all is well for you handling the logs, and not really care once you have them in LA.  :)  Just be cautious.
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

Walt900

I'll try again.

Here is a site with a log weight calculator.

https://forestryforum.com/board/index.php?action=toolbox The original Wood Calculators<<<<  &metric=

SwampDonkey

Walt, we have a site right here for that, it's that toolbox in the bottom left. They are based on green volumes from the Wood Handbook and Huber's volume equation (mid diameter). What I attempted to show is that specific gravity changes when you loose bound water along with Vol shrinkage. MC% is calculated based on a fraction of Oven Dried Weight. Those moisture meters I've been told aren't very accurate above 30 % MC.  And......



[Source: Textbook of Wood Technology]


By definition,

FSP = Volumetric shrinkage from green to oven dried/Specific Gravity in green condition

So, it's obvious "green" figures being used in the Wood Handbook are at 30 % MC.

They are the same figures in the "Textbook of Wood Technology".
"No amount of belief makes something a fact." James Randi

1 Thessalonians 5:21

2020 Polaris Ranger 570 to forward firewood, Husqvarna 555 XT Pro, Stihl FS560 clearing saw and continuously thinning my ground, on the side. Grow them trees. (((o)))

knowslittle

Beenthere-  yes, the yard said from Montana, but I don't know if they are dead or not. Easy question to ask though.

Walt- Thank you. . .thats extremely helpful.

Swampdonkey- If you are referring to the Wood Handbook put out by the Forst service, then I have a question for you.  In my copy (1999 edition) Table3-3, p. 44, "Ave. Moisture Content of Green Wood" says the MC of lodgpole pine heartwood is 41%, and sapwood is 120%.
Am i missing something here? Why would their tables reflect a "green" MC @ 30% yet the table above talks of a much greater percentage on moisture when green?
Not questioning you exactly, just trying to understand how the number is arrived at.



  And if the table you offer is for an MC of 30%, any idea how much to add to the weight if the log's MC is 85% per Walts offering, or even greater as one might imagine by reading the table I cited?  I realize to be accurate you'd have to ascertain the true MC, and that in itself is probematic.


  As to the moisture meters, yes you are correct.  I have a 30 year old Ligno with 2" drive in pins,  and the maunufacturer says it isn't accurate for MC greater than 30% or thereabouts.

As always, thanks to all,
Bob

Jeff

Quote from: Walt900 on September 18, 2010, 08:23:13 AM
I'll try again.

Here is a site with a log weight calculator.
https://forestryforum.com/board/index.php?action=toolbox The original Wood Calculators<<<<  &metric=

There is a story I'd like to tell again about how that other site came to have volume calcs, but I'll let it slide. Most of our old members know about it, but lets just say I won't be allowing links to them when we have the originals right here.  No, no I won't let it slide because it still pithes me off. How we found them via our referral links, with our code, and with our copyright and little toolman graphic that led us to them still intact on a part of their website that was labeled "secure"  But they were emblazoned with their logo in place of ours.

The story was that they were "Evaluating them" before they asked us permission to use them.

You can go clear back here to find reference to it, almost 10 years ago. I still pith myself off on how I let it go.  They used ours for a couple years through an agreement I agreed to. Just long enough to find someone to develop their own. One of ours is actually still there.

https://forestryforum.com/board/index.php/topic,576.msg5996.html#msg5996

I've made an adjustment in our software to direct people to the originals.
Just call me the midget doctor.
Forestry Forum Founder and Chief Cook and Bottle Washer.

Commercial circle sawmill sawyer in a past life for 25yrs.
Ezekiel 22:30

SwampDonkey

Yes, I see my assumption about the tables at 30 % MC is not so by looking at the table I have here.

That FSP formula is used to determine the FSP using those tabulated figures, by assuming FSP of 30 % you can't get those tabulated figures in reverse. Some species there have a FSP of 20, 26 or 35. You have to calculate FSP from their empirical figures in the tables then proceed to find your log weight.

My mistake there. ;)

For lodgepole: Sp Gravity green is 0.38/green weight is 39 lb/ft3/Vol Shrinkage is 11.1% from green to oven dried.

FSP = 11.1/0.38 = 29.2%

MC% of 85% in logs means the specific gravity in green condition is unaffected since shrinkage did not occur. All you need to do is multiply specific gravity (green= 0.38) by volume and density of water (62.4 lb/ft3). Let's use 50 ft3 again

Wo= 0.38 x 50 x 62.4 = 1186 lbs oven dried weight (see next post). We would have lost about 4% of volume (2 ft3) if we dried to 20 % and specific gravity would increase because we are loosing bound water.

You have to remember when wood looses bound water, below FSP, we have changes in the wood other than water weight loss. Small losses in bound water doesn't add up to much difference in SP Gravity from green condition. Someone is going to have to weight that wood, either the supplier or buyer. Any wood I sold, the buyer paid on delivered weight through their mill gate.

As we all stated before it's safest to calculate with green figures because it gives you a safety margin. That's if your relying on something where your hoisting a weight into place or load of that piece on the structure being constructed. It's the heaviest the wood is going to be.
"No amount of belief makes something a fact." James Randi

1 Thessalonians 5:21

2020 Polaris Ranger 570 to forward firewood, Husqvarna 555 XT Pro, Stihl FS560 clearing saw and continuously thinning my ground, on the side. Grow them trees. (((o)))

knowslittle

Jeff- If I stirred up the honey bucket. . sorry,  did not mean to do so.

Swampdonkey- Great explanation.  I actually did those same calcs based on 17 cu.ft prior to reading your post and came up w/ the correct answer. But call me thick, but why does the log weight calculator on this site differ so much from the calcs you/I use?  What am I missing?
Thanks again for your time a explanation!
Oh. . .and I wasn't trying to call you on anything. .  .just trying to understand it all.
bob

SwampDonkey

Because me and my brain lapse did not add the weight of the water. ::)

We only found OD weight. DOH!

W85% = Wo + 85/100 x Wo
           = 1186 + .85 x 1186
           ~ 2194 lbs   It appears that green lodgepole is around 64.5% MC on average.

    0.3 x 120% + .7 x 41% = 64.7% if you assume there is 30 % sapwood.

1186 + 0.645 x1186 = 1950 lbs  but you won't see that in the formula they are using, they are just taking the tabulated green weights from the table in the Wood Handbook, which are averages for each species per cubic foot of solid wood and multiplying by Huber's volume for a log of measured length with measured mid diameter.

I checked some other green volumes for lodgepole and it seems to be the case.
"No amount of belief makes something a fact." James Randi

1 Thessalonians 5:21

2020 Polaris Ranger 570 to forward firewood, Husqvarna 555 XT Pro, Stihl FS560 clearing saw and continuously thinning my ground, on the side. Grow them trees. (((o)))

knowslittle

Hey Swampdonkey, thanks, but I'm still not following you, but I'll keep working on it as time allows.
bob
 

SwampDonkey

They are tabulated green weights lbs/ft3 used in the forum toolbox taken from the "Textbook of Wood Technology".

Talking here about wood that is green, 85% we used previously as the MC. What we did earlier here, a couple post back was we only calculated oven dried weight, symbolized as Wo.

Wo=Gg x Dw      Gg is specific gravity when green, Dw is density of water

Specific gravity in green condition from the Wood Handbook along with density of water, was used to calculate Wo. Since the wood is already green we did not have to calculate partial volumetric shrinkage and a dryer specific gravity. We have to then add weight of water above oven dried condition to get weight at 85% MC in our example. In this case the fraction of the weight due to water is 85% of the weight in wood substance when oven dried, so we added that water to the total weight to get green weight.

I later explained that Lodgepole averages out to around 64.5 % MC (64.7% precisely when we do the math as noted above)  when we assume the sapwood portion is 30 %. If you calculate it out using this instead of the 85% previously you get nearly same figure as the Forum Toolbox, maybe a little heavier.

Pages 3-11 and 3-12 in the "Wood Handbook" explains the methods I've presented.

Another example: Beech= Sapwood 72% MC, Heartwood 55% MC, Gg=0.56

0.3 x 72% + 0.7 x 55% = 60% MC on average when green  (Table 3-3), Beech 54 lbs/ft3 green from Forum Toolbox drop down list of species.

A 16 foot log with a 24 inch mid diameter has 50 ft3 (Huber method) of green volume according to the Forum Toolbox and weighs ~2714 lbs.

Calculate oven dry weight of beech. (Table 3-7b in "Wood Handbook"-moisture 0%)

Wo = 0.56 x 62.4 lbs/ft3 = 34.9 lbs/ft3 oven dried

Calculate Green weight (60% MC) also can be looked up in Table 3-7b

W60 = 34.9 lbs/ft3 + 0.60x34.9 lbs/ft3 = 56 lbs/ft3

50 ft3 green x 56 lbs/ft3 = 2800 lbs

The weights in the Forum Toolbox are in the "Textbook of Wood Technology". I can't find green weights for all species listed out in the "Wood Handbook". But, we got them mathematically anyway using methods explained in the Wood Handbook. The math tends to yield slightly heavier results. I think you can assume that is a result of constantly rounding numbers.

Remember to calculate your Fibre Saturation Point (FSP) of the species you're air drying to see if the MC% of the wood is below that. Thus partial volumetric shrinkage is occurring, which results in higher specific gravity. You'll have to calculate new specific gravity (Gmoisture) in order to get the proper oven dried weight (Wo), then air dried weight (Wm). From post #2, repeated in posts 14 and 16.
"No amount of belief makes something a fact." James Randi

1 Thessalonians 5:21

2020 Polaris Ranger 570 to forward firewood, Husqvarna 555 XT Pro, Stihl FS560 clearing saw and continuously thinning my ground, on the side. Grow them trees. (((o)))

knowslittle

Thank you swampdonkey, much better for me puny brain to understand.
Great info, but now have to buy a copy of "Textbook" .

Bob

SwampDonkey

No, don't have to buy anything. If using green logs you can note the green weights from the Forum Toolbox or use tables 3-3 (30% sapwood, 70% heartwood), 3-7b and 4-3b to work it out on your own like I did above. With air dried below FSP use tables 3-5 (Vol Shrinkage %) and  4-3b (Green Specific gravity) of the "Wood Handbook" to calculate species FSP to get specific gravity below FSP moisture threshold (Gmoisture) due to volumetric shrinkage, then oven dried weight (Wo) and finally add the water weight to get total weight at determined moisture content (Wmoisture).

Huber volume in the ToolBox is:

VolumeHuber = length of log (feet) x mid log Diameter2 (inches) x 0.005454 = ft3

Wmoisture x Volume = weight of log volume.

You already have the "Wood Handbook" off the USDA site.
"No amount of belief makes something a fact." James Randi

1 Thessalonians 5:21

2020 Polaris Ranger 570 to forward firewood, Husqvarna 555 XT Pro, Stihl FS560 clearing saw and continuously thinning my ground, on the side. Grow them trees. (((o)))

knowslittle

Thanks again.  When I can get some time away from work ( no, not complaining) I'll study your info..
  Swampdonkey, you took alot of time explaining this for me and I do appreciate your efforts very much.
  The folks on this site are truly unique!

Probably buy the darn book anyway, seems  I end up researching more and more when work gets slow, and never seem to regret it.

Bob

SwampDonkey

It may be difficult to obtain unless used and will not be cheap. This whole thing may be academic in nature, but it's a whole lot better (safer) than any WAG. ;D
"No amount of belief makes something a fact." James Randi

1 Thessalonians 5:21

2020 Polaris Ranger 570 to forward firewood, Husqvarna 555 XT Pro, Stihl FS560 clearing saw and continuously thinning my ground, on the side. Grow them trees. (((o)))

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