Why Saw Lumber Thinner?
Sawmillers discuss the economics and practicality of sawing 12/4 versus 4/4 lumber. January 13, 2006
Question
I'm a cabinet and furniture maker, and this question has baffled me for quite some time. If 4 quarter lumber, any species, sells for $3.00 a bd/ft and 3" lumber of that same species sells for $7.00 bd/ft, why would anyone saw 4 quarter? Isn't there more labor and more machine wear and tear sawing and stacking 12 to 1?
Forum Responses
(Sawing and Drying Forum)
From contributor A:
It sounds great in theory but there is only limited demand for 12/4, and a huge demand for 4/4. $7 a bd/ft doesn't do any good if it sits on the shelf. Additionally, it takes a premium log to yield more than one or two FAS 12/4 chunks. Many times when you cut deep like that, you run into unseen defects, and suddenly that piece that looked like FAS on the open face grades out 1 or 2 Common on the other. By cutting 4/4, I can keep rotating that log, always taking the best face and being able to read the log a little better on what is in store for the next board. From a physical standpoint, I can toss around 4/4 boards all day but 12/4 boards take a toll on me.
From contributor B:Contributor A is correct about the sawing side, and another reason is the drying. 3" boards are just more difficult to dry. Either they need to be kiln dried on a very gentle program, which takes much more kiln time, or they need to be air dried, for a year or two, then kilned. Also they are unusual size, so expect to pay more just because of that. Add all those factors in and yes, they will cost twice as much.
From Gene Wengert, forum technical advisor:Two very excellent comments so far. As a rule of thumb, 20" diameter or smaller logs will not produce any 12/4 upper grade lumber. Drying time is about 4x, (unless you use contributor C’s vacuum kiln) plus with a species like oak, the amount of checking would be excessive even with the greatest of care. Another reason is that the weight of 12/4 lumber is roughly 3x the weight of 4/4, so the lumber handling can be difficult in some cases.
From contributor C:One of my partners believes that dry milling will be a part of forestry processing in the future. I keep drying bigger and bigger pieces of wood. The last load was flitch-sawn 3" red oak that dried to 6% in 11 days. My partner's idea is that you saw from these dry flitches. It sounds right when you consider how much wood is wasted when you mill 4/4 down to .75". It is especially bad if the 4/4 was actually 1.125” or even 1.25" thick. Why not just saw to .75"? Look at the waste from the edger. And after the lumber is dry, you cut away more to get straight, parallel edges. Why not cut the width you need? Maybe dry milling will make sense in the future. Then, if your valuable 3" won't sell, cut it to the size that the market wants.
From contributor D:Regarding contributor C’s dry milling of lumber - when an oak board is sawn 1.125 and dried, you end up with 0.75 lumber because you allow for shrinkage, and plane out cup and saw marks. There is some waste but it is clean lumber.
If you dry larger chunks of lumber you may resaw at 0.90 and then plane out saw marks. You will have to saw out the cup before you resaw, so there will be waste there. It is hard to saw dry oak as opposed to green so speed will have to be considered as well as saw cost of blades and filing. Vacuum kilns are expensive and the cost of operation is high. That factor may then price the lumber over the cost of waste gained by green sawing and drying. As more large mills process the chips into other products or burn in boilers to recover energy costs, there is in fact less waste.
12/4 wood is not used nearly as much as 4/4 in cabinet building. Supply and demand is the first rule of economics. The demand is mostly for 4/4 and the suppliers produce mostly 4/4, so it goes hand in hand. As cabinets go more and more to 3/8 MDF with paper faces that look like boards we will just start chipping every tree and stop sawing lumber all together.
From contributor C:To contributor D: The cost of operating a vacuum kiln is higher per hour per bf than operating a conventional kiln. But, if the vacuum kiln dries in 3 days what might take 30 days in a conventional kiln, the drying cost can be less than the conventional method. The drying cost was higher in our old systems but we are testing a modification that reduces operating costs when drying rate is reduced.
From the original questioner:It sounds like the answer to my question is market demand. The dry sawing sounds like it could be interesting but I imagine the whole deal would work better with slow air dried flitches. I know when we resaw from chunks we've had for a few years the bowing and warping is minimal compared to similar kiln dried. The average moisture content here for 4/4 not in a climate controlled environment is about 12% year round, so it takes a good long while for the chunks to dry.
