Recovery rates?

[sawmillsi]

As an Australian (have grown up in the metric system, but know some imperial) I find the American system of recovery rates ambiguous and confusing.

In Australia the recovery rate is calculated as the amount of timber recovered over the amount of timber within the log.

Eg. Log is 4m3, timber recovered = 3m3, therefore 75% recovery rate.

NB. 450 board feet = 1m3

It is very black and white.

Yours however seems to have a fair amount of guess work, witchcraft of a lot of luck? ??? ??? ???

[Hokiemill]

I'm not so sure that there is much difference in the way we figure it out.  You didn't address the biggest variable and that is how do you determine the 4m3?  We're doing the exact same thing - volume in log versus volume of boards actually cut.  It just so happens that we utilize primarily three different ways to estimate log volume (doyle, scribner, international 1/4").  If you are using a log scale to determine your 4m3 then we're all doing the exact same thing.

100% recover means you got what you scaled.  If you get more actual lumber than what you scaled in the log - now were talking 110% or 120% recovery, etc.

[Frank_Pender]

In this neck of the woods we use the Scribners system. It  is very antiquated as far as I am concerned.     With my mill I get no less than 25% overrun.  What that means is that the log might scale out at 100 board feet and I get 125 bdft of lumber. Most of the time I am running around 35% overrun, but that is primarely determined by the size of the lumber I am cutting at the time.  The majority of my lumber is dimension Douglas Fir, ranging in sixes from 2 x 4s to 2 x 12s and some 4 x material for header stock.

   At one time several years ago the Williamette Industries mill, here in Dallas, Oregon was considered the most efficient mill in the world.  Now that Weyrhouser  has taken over, who know, but earlier they were running at about 200% overrun based on the dimension of the logs there were purchasing: 32' - 42'

[ARKANSAWYER]

  SIZE matters here.  Most of the logs I saw are under 30 inch dib.  The scales really dock logs under 18 in.  A 12 inch log will scale 32 bdft but I can saw 50 to 60 from it.  It is that way to keep the loggers from bringing in a bunch of small sticks.  Most mills do better with logs in the 18 to 40 inch range and make the most coin for their effort.
  Also another thing is the size of the boards sawn.  If I am cutting 2x soft wood and I saw it 1 5/8 thick but charge for a full 2 inch board then it does not take long for my overrun to really count up.  I always saw every board from the log so I always get 100% of what is in there.  But I can get 125% or better of most scales with my band mill.  Some folks just lie about it all and have not a clue of what they are getting.  I went and watched a feller saw one day and he claimed to get 200% of the Doyle scale.  He was doing some "fuzzy math" and left alot of barky edges and most of his lumber was not fit to use.  Not in business any more.
  Just try to get all that is in there and charge a fair price and it will go well with you.
ARKANSAWYER

[Ron Wenrich]

Well, it all depends.  There are 2 ways of stating yield:  as a recovery factor or as overrun/underrun.  

The Lumber Recovery Factor (LRF) is figured out by dividing the lumber yield (in board footage), and divide that by the cubic volume of the log.  You'll end up with an LRF factor, usually around 6-9 bf/cu ft.  It will vary by log size, just the way your recovery rate does.  

The problem arises in that most guys don't use a cubic volume to measure their logs.  Most go by the board foot method.  Its something that the logger, landowner and miller can all agree on and comprehend (usually).  

Overrun is figured as  % overrun = (lumber yield/log scale) - 1 * 100   You can also figure your overrun from tree scale to log scale or tree scale to lumber yield.  So, a 25% overrun would mean that you get 125 bf for every 100 bf scaled.  

The measurements are useful, but there are tons of variables.  Being able to get a handle on it is worthwhile, but most guys don't do it.

The LRF factor is a more accurate method.  Cubic scaling is a little different than board foot scaling.  Then you also have 3 different formulas for figuring out cubic foot or metric volume.  So, which do you use?  

[sawmillsi]

All the posts too date have just confirmed what i thought - confusing.

I'll give you an example from the weekend (doing a demo at a local feild day - pics to follow soon):

Logs Slash Pine (Pinus elliotii); 0.315m diameter, 3 meters long.

Volume = Radius^2 x pi x length
OR
0.1575x0.1575x3.141x3 = 0.23375m3

I recovered nine 6"x1", two 4"x1" and two 2"x1"
OR
0.12375m3

Recovery rate = timber recovered/volume of log
OR
(0.12375/0.23375)*100 = 52.9%


PS. Normal practice is to do 2 x diameters at each end of the log and average them out - also the diameter is under bark.

Is this method easier?

From this I know that 47.1% of the log went as sawdust and firewood (probable most as sawdust even though I was using the Peterson Ultra-Thin kerf blade - 3.8mm).

Simon

[Ron Wenrich]

I think you'll find those rates will vary as the size of your timber varies.  Larger trees have a better recovery rate, doesn't matter if you are using LRF, cubic meters or any other type of measure.  Each size class will have a different recovery rate.  Confrising, no matter what you use to measure.

After you have the knowledge, you have to know how to apply it.  With the right set of variables and the right set of data, you will know which logs are profitable to mill and which logs belong in the firewood pile.  

Those that can tell the difference get to play the game a little longer.  Those that can't have to set out on the sidelines until they can get enough smarts and cash to get back in the game.