Quantity of Sawmill By-Products

      How much bark, chips, and sawdust do sawmill operations produce? That depends on many factors. August 30, 2005

Question
I am wondering how much waste is obtained from 1000 board feet (1Mfb) of lumber production, and in what proportions of bark, sawdust, and shavings?

Forum Responses
(Sawing and Drying Forum)
From contributor H:
Roughly 2/3 of the log becomes lumber. I’m not sure of the proportions of dust, bark, and chips.



From contributor B:
I produce zero waste with my bandmill. I do have some by products, sawdust, slabwood and edgings. I agree with the 2/3 lumber from the log and it could be closer to 3/4 with a bandmill with its thinner kerf.

As far as the proportion, with a band I would say the bark and wood fiber is about equal with the sawdust being a lesser amount. If you are talking about shavings from surfacing, with 4/4 lumber you are planning off about 1/4" so that would make 1/4 shavings and 3/4 finished would, not allowing any reduction for jointing the edges. The ratio changes with the thickness of the finished product, and that goes for sawing and surfacing. The less sawcuts that are made the less waste you would have.



From the original questioner:
I stand corrected with regards to the term waste. By-products would be more accurate. I am looking at amounts for fuel production calculations, so really none of it would be wasted. What I am looking for are some actual measurements, in tons, pounds, or cubic meters, etc. Would I be correct in assuming the average output from 1Mfb would be approximately 1 ton total of bark, sawdust, and shavings, in proportions of 5:4:1 (by weight) respectively?


From contributor F:
The answers you are seeking is/are a relative item. Dimensions of the lumber produced, amount of wane allowed on corners or edges of lumber, etc. I can produce lumber from a long and have whole bunches of fiber not turned into usable lumber by making the boards all 1" thick and 2" wide, or cut the log into one large cant of 16" thick.


From contributor D:
It depends too on what you are cutting, a nice straight white oak with little or no taper you have four small slabs and some sawdust. A crooked log, a gnarly egg shaped cedar with big furrows in the bark, a sweet gum log that is 24" at the butt and 18" at the top, a walnut with unusually thick sapwood, or a sound looking log with just a little spot on the butt that turns out all but worthless inside because it’s rotten, hollow, and bug eaten. I am sometimes unpleasantly surprised by the amount of byproduct relative to the quantity of lumber I was planning to saw.


From contributor B:
Log size greatly affects ratios of lumber and waste. Four logs 20" in diameter and 16' long will give over 1000 board feet of lumber with only 16 slabs. Ten logs 14" in diameter and 16' long will give 1000 board feet and 40 slabs. Sawdust amounts remain almost the same. The thickness of the lumber will change the amount of sawdust produced.


From contributor H:
A fellow at a paper mill told me that his rule of thumb for hardwood lumber is 1000 board feet lumber produces one ton (2000 lb) of clean chips and 3/4 ton (1500 lb) of bark and sawdust. The volume would be similar but the weight would be less for softwoods.


From contributor R:
I helped to site a co-gen plant about twenty years ago. Our rule of thumb was about two tons of slabs and one ton of sawdust per Mbf of lumber. That is for hardwoods, and it held out pretty well. If you are cutting softwoods and not using nominal sizes, you will get more footage vs. by-product. You have to know your conversion rates.



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