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Author Topic: Tree to board calculations...  (Read 896 times)

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Offline MapGuy

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Tree to board calculations...
« on: August 07, 2018, 12:20:39 AM »
Hi there,

New to the forum here. Have gleaned some great information so far!

My previous career was actually a forestry technician, but, I seem to have forgotten most of the lingo/calculations, etc. So, I was wondering if anyone would care to validate a calculation I put together, but first the background; I have 15 acres of Douglas Fir and Ponderosa Pine. I'm looking to have a friend with a portable mill come up and mill me some fencing materials. So, I made some calculations to see whether it would be worthwhile or not. Here are my calculations:

Average Douglas Fir
121cm or 47 inches circumference (15 inch diameter)
13m tall or 42 ft
= approx 0.7 m3 volume. (Wood volume calculation using taper models)

1 - 4" x 4" x 8.5' pole = 11.3 board feet
1 - 2" x 6" x 8.5' board = 8.5 board feet

0.7 m3 volume = 295 board feet.

So, in theory 295/11.3 = 25 poles or 295/8.5 = 34 boards.

Does this make sense?

Thanks in advance,

Mark

Offline Ianab

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Re: Tree to board calculations...
« Reply #1 on: August 07, 2018, 02:32:10 AM »
The maths looks correct, but it doesn't take into account the actual cutting patterns and product you are wanting. 

For example if one of your logs ends up 10" at the small end, and you want all 4x4s, you are going to be slightly disappointed, as some of your bd/ft are going to be something other than your target. And except in some very unique circumstances that's going to be the case for any log size. 

BUT, most band mills can get some over-run on the log scale because the log scales account for a 1/4" kerf circle mill. The band mill can eke an extra board or 2 out of most logs. 

So I guess what I'm saying is you might be able get 295 bd/ft out of your tree. But you can't guarantee that it will be 25 4x4 posts. But with 2 target sizes and a clever sawyer you might get close. 
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

Offline moodnacreek

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Re: Tree to board calculations...
« Reply #2 on: August 07, 2018, 08:08:16 AM »
I would start with a tree scale stick to determine how many 16' logs you have.

Offline ChugiakTinkerer

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Re: Tree to board calculations...
« Reply #3 on: August 08, 2018, 09:34:25 AM »
Welcome to the forum!  There are a few handy calculators you can compare to using the Forestry Forum Toolbox.  The vertical banner on the left side of the screen has a bunch of sponsor links.  At the very bottom is a red toolbox.  Clicking on that will give you the toolbox, which has numerous useful calculators.

The direct link is: ToolBox

You can run your numbers a couple different ways, by tree or by log.  I tried to emulate your measurements using those and come up with much lower numbers.  My guess is that you're likely to get 150 to 200 bf per tree, using the international scale.
Woodland Mills HM130

Offline jb616

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Re: Tree to board calculations...
« Reply #4 on: August 12, 2018, 09:14:32 PM »
Has someone thought of putting these different calculations from the Toolbox on an App so that we can figure it out on our phone?  

Offline Magicman

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Re: Tree to board calculations...
« Reply #5 on: August 12, 2018, 10:08:19 PM »
Yes, Jeff has made the Toolbox "phone friendly".  Scroll to the bottom of the page to find the Toolbox with your phone.
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Offline Brucer

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Re: Tree to board calculations...
« Reply #6 on: August 13, 2018, 01:18:22 AM »
Mark, you're using a calculation from Natural Resources Canada. Keep in mind that in Canada (or at least in BC) logs are sold by the total volume of sound wood, not by the recoverable volume. My experience from sawing over 400,000 BF of Douglas-Fir lumber and timbers is that for each cubic metre of wood you will get about 200 BF of timbers plus 100 BF of 1" lumber off the sides of the log. Of course the timbers could be sawed into lumber instead.

My numbers are based mainly on logs that have 12" tops (inside the bark) and with lengths of either 43' or 52'. Smaller diameter logs will give you less recovery per cubic metre.
Bruce    LT40HDG28 bandsaw with two 6' extensions.
"Complex problems have simple, easy to understand wrong answers."

Offline jb616

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Re: Tree to board calculations...
« Reply #7 on: August 24, 2018, 06:19:27 PM »
Yes, Jeff has made the Toolbox "phone friendly".  Scroll to the bottom of the page to find the Toolbox with your phone.
I even made it a favorite and put it on my home screen!  


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