Rotating logs when sawing
If I'm cutting low grade or building lumber, I will turn 180 degrees. I cut opposite sides until the log is the width of the material needed. When sawing large logs, I turn back to the first face to size the cant so the log doesn't bow from uneven stress release. When sawing higher grade logs, I turn 90 degrees to get more high grade lumber.
Remember that 180 degrees from the first to second face is used only when you can do it safely. For larger logs, you may need to go 90 degrees on some mills to assure log stability (and safety).
The advantages of 180 include wider pieces, less edging, less side bend when drying, flatter grain, and less log spring.
If we assume a 24 inch log (it works for any size, however), you can see that the best way (180 degree) results in 8 pieces needing edging, while the poor method results in 13 pieces that need to be edged. This alone is quite significant in terms of workload for a small saw-miller.
Next, the following tabulation shows the difference in lumber size. The best method produces more wide pieces, which are more valuable.
Width of lumber/Number of Pieces
20" wide...2 pcs at 180 and 1 pc at 90 degrees
17"...2 and 1
15"...0 and 1
14"...2 and 3
13"...0 and 2
11"..10 and 8
10"...2 and 1
In addition, there are 8 pieces in the poor method that have rings that are not centered, edge to edge, which means that these pieces are likely to develop side-bend in drying.
In addition, if this is a species like walnut or red oak with a narrow band of sapwood, in the best method, 10 pieces will have sapwood in them; in the poor method, 13 pieces. Sapwood causes drying problems (checks easier for oak) and also color problems for some customers.
Finally, on many mills, 180 degree rotation provides a much more sturdy and safe rotation method.
Gene Wengert, forum technical advisor
A lot depends on the log. Some logs just won't lay that well against the headblocks. (Running a circle mill).
Target sizes for most hardwoods are: 7x9, 7x8, 5 1/2x6, and 3 1/2x6. There are also variations to get multiple pieces of blocking from the lower grade logs.
Using the 180 degree method often gives a lot more 6" boards than turning down. Also, some of the wider boards have to be re-edged for upgrade.
I find that turning down gives me better grade yield and I can cut higher priced tie and bridge stock easier. Grade sawing is knowing when to stop and turn it into blocking.
You really have to look at the species and your market for whatís best for you. Our log average is over 24" in diameter in cypress, but there is little call for 20" boards out there and also the boards are more apt to cup and split. We stress flexibility on our cutting. On the smaller log we may rotate 180 degrees to gain width or if it is knotty. But on our bigger logs we are shooting for 1 x 12 and grade--taking off each side is the best way. Donít get me wrong--we donít just take off so much of each side and let it go at that. We make several cuts and then turn and go 90 degrees until we are squared. If cant is over 12" we take each side down by grade before we either leave as a timber or cut into 1 x 12. This gives us our best grade and also relieves stress.
What if the 2nd best face is not on the opposite side of the best face? Would this not dictate how much we turn or where we turn to? 1st then 2nd then 3rd no matter where it is on the log?
There are two choicesóopen the best face with full taper, or open the worst face with no taper. (Of course, on a large, high grade log, we use full taper on all faces.)
We then rotate 180 whenever possible to maximize quality, as discussed above; such quality concerns include warp in drying (which some people here have not addressed), as well as edging work-load.
Your question is answered if we factor in one more concern--when to rotate the log to a new face. If when you rotate 180 and then take off a slab (or maybe one or two pieces of lumber to increase the flatness of the face, balance the stresses, etc.), you leave this second face whenever the grade that you estimate will be produced from this second face will be lower than the grade produced from the 3rd or 4th face. Of course, this is a judgement call. However, if the 2nd face is a poorer face than the 3rd or 4th, you would not stay on the 2nd face long enough to drop the yield on the 3rd or 4th face.
Remember that for a log there are probably over 1.5 million ways to saw the log. The 180 rule is one part of a set of instructions on how to maximize the value and conserve natural resources. Because the set is a general set of rules, you will need to factor in common sense now and then. But, day-in and day-out, the 180 rule and the entire set of rules will be the best (if done safely).
Gene Wengert, forum technical advisor
When we saw for VG in red cedar or yellow cedar, we split the log about 3" up from the heart. We offload that slab, rotate the remaining slab and cut about 2" of the heart. So now you have 3 slabs that will yield about 80% VG depending on how you saw them. This method is very common at big mills that ship to Asia.
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