Sawmill and Treating Insights
How to produce the most value from a hardwood log is always an interesting topic of discussion at trade shows and field days.
There are many different ways to produce value when sawing. One can focus on producing the maximum amount of volume in a day’s time, cutting the highest grade or value board with each pass of the saw, or some combination — such as taking time to get the value and then sawing the remaining material quickly.
The method used should be based on the raw material you are sawing and the market for which you are sawing. Keep in mind: you should always be able to justify how you saw based on your market.
There are typically three methods of sawing a log. The first is live sawing or through-and-through sawing, the second is cant sawing, and the third is grade sawing. (Figure 1)
In live sawing, cuts are made into the log until the center is reached. Then the log is rotated 180 degrees, and the remainder of the log is sawn by the same method.
In cant sawing, slabs and one or two jacket boards are removed until a cant is produced. The cant is then sold as is or live sawn into boards.
The final method is grade sawing, where the log is sawn and turned in a manner that produces the highest possible grade return.
Most custom sawmills charge their customers based on a production rate, hourly rate, share basis, or they sell lumber based on the grade. The sawing strategy you use should depend on your pricing method. Do not spend time grade sawing if you are being paid based on a production rate.
The main idea behind sawing for grade is that while the defects on the log cannot be moved, using your knowledge of lumber grading rules, you can rotate the log to place the defects where you want them to appear in the boards sawn. This requires that you have some knowledge of lumber grading rules. A good sawyer is an expert grader. Most lumber is graded using the National Hardwood Lumber Association’s Grading Rules. I encourage anyone attempting to saw for grade to obtain a copy of these grading rules and attend a lumber grading class. If you are selling lumber based on custom lumber grades, then use those for sawing decisions.
Selecting the first face to saw, or the opening face, is of great importance. This first saw line will determine the grade of boards produced from the remaining cuts. If there are few defects on the logs, try to place the defects at the edges of the flitches to be produced. This will give you the opportunity to cut the defects out when the board is edged.
When sawing for grade keep in mind the potential sawing faces. The deeper you saw into one particular face, you remove potential volume from the two perpendicular faces. Since random width boards are used in hardwoods, the extra width you can place into a high grade face will increase its volume and value. Be careful because if you cut too deep into a face with lower grade, then you may remove volume from a potentially higher valued board on one of the other faces. (Figure 2) This is the second most important concept of grade sawing.
Determining the best face to cut is a lot easier with the bark on the log; knots and low to medium bumps are easy to identify. Since most portable sawmills saw logs with the bark, grade sawing is easier. On debarked logs, it can be very difficult to see defects, especially when the surface is rough. If you are curious about how to identify defects in logs, I would recommend that you check out the hardwood defect trainer Web site at the Michigan Tech forest resources and environmental science program (http://forest.mtu.edu/research/hwbuck/hardwood_defects/index.html).
Whether to turn a log 90 degrees or 180 degrees has always been a topic of great debate. Turning logs 180 degrees results in less edging and greater stress relief when sawing. However, it requires more time for turning logs.
This takes less time on large mills with rapid turners, but on small portable mills it can significantly reduce production time, so many portable sawmills turn 90 degrees. If you did not buy a log turning option on your mill, then I would highly recommend turning 90 degrees!
When logs are larger on one end than the other, they have taper. Taper settings are methods to handle the taper that occurs in the log to maximize volume and grade recovery. When working with taper settings on a portable sawmill, I have always found it easier to keep track of what my taper sets are with turning 180 degrees.
When it comes to log turning, there is no definite right or wrong solution. Each has advantages and disadvantages. Use what works best for your situation.
Stop Turning When?
Usually, a log is turned when the grade of one of the remaining faces is higher than the face you are currently sawing. This will result in maximum value return for the sawyer.
The sawing cost in time (turning the log, slower production) will reach a point when — considering the value of the lumber — it is best to saw through-and-through or leave the remaining material in cant form. When do you stop turning the log for grade? It will depend on your local market.
When you saw deeper into a log, the grade drops. In certain species this is rapid, and in some you can saw quite deep. In my opinion, when the grading faces drop to grade No. 2, it is time to saw through-and-through. The difference in value usually is not enough to warrant the time for continued turning and decision making.
I find that most of my decision making in turning logs comes with mid-grade saw logs. High-grade logs are easy since they usually contain few defects. Low-grade logs are easy since they have lots of defects. Mid-grade logs are usually where the largest value gains or losses are made.
Sawing for grade can help increase the value produced in any hardwood sawing operation. Follow some of these basic suggestions and you will be on your way to making higher grade lumber.
If you are interested in more information about grade sawing, I would suggest downloading a copy of ‘A Simplified Procedure for Developing Lumber from Hardwood Logs,’ available from the Forest Products Laboratory at www.fpl.fs.fed.us/documnts/fplrn/fplrn98.pdf. While somewhat dated, the basic concepts have not changed.