Posted on May 02, 2016

Sawing logs into lumber has become more of a science than anyone ever thought years ago when steam powered head rigs broke down enormous cedar logs that existed in seemingly endless volumes on the Pacific Coast.

Today’s sawmill is focused on recovery and optimization, smaller target sizes and minimizing kerfs, along with high speeds. But with seemingly everything we do in a sawmill, there is a balance where chasing recovery in the sawmill can cost you dollars in the end.

Achieving maximum recovery basically means that you are trying to capture all the useable wood fiber in a log, and saw it into boards that you can sell. Right off the bat, recovery is gained in the way logs are scaled. Mills target LRF (lumber recovery factor) numbers in excess of 2.5. In simple terms, that means you pay for 100 meters³ of log and produce the equivalent of 24,000 BF of lumber. That’s just good business. But there are other factors to weigh when thinking recovery.

By product:

When you saw logs into lumber, step one is to remove the bark.

There are recovery opportunities here that if done incorrectly, can cause issues in the finished product which will cost you recovery in the end. Tearing into the white wood fiber of a log with de-barking equipment will definitely cost you volumes of lumber and in loss of potential chip volume that wind up in hog.

The torn fibers can also wreak havoc on optimizers that may see logs larger than they are, resulting in shallow cuts at the primary breakdown centers where boards are expected but not realized and wind up as chips or low grade. These fibers also add to your fines percentages in chip samples costing you valuable CQI (chip quality index).

Climate, weather and feed speeds can contribute to these issues along with the fiber itself and of course the setup of the de-barkers.

Primary breakdown machines and optimizers:

Optimizers, scanners and their related components will only do what we tell them to do.

Generally, they are very accurate and reliable and do a really good job of creating solutions in a very short time. Scanned LRF numbers generated in reports from the optimizer are usually higher than actual LRF because they see the log before any breakage, losses or other issues that may happen in the mill.

They also make these solutions based on the parameters put in by the mill. If you set parameters in the optimizer that call for a narrow, short opening face, the optimizer will do this based on your parameters and the accuracy of the scanner, DLI (double length infeed) and log positioning systems. If any one of these areas is amiss, the actual face coming from the breakdown center may be larger or smaller than expected, resulting in recovery loss.

Faces near the outside limits of the parameters can potentially become chips at drop sort tables or trimmer optimizers. Your optimizer called for a 2x4, 8’ No.2 but due to the face being too light, it became an economy or worse yet, chips. Opening faces too wide can leave good fiber on the slabs, again this will go into chips.

The mechanical setup and maintenance of the equipment is very important so that sloppy clevises or miss reading temposonics don’t place chipping heads or saws in the wrong spot in correlation with the optimizer’s requests.

Running target sizes too small, below capabilities looks great on paper, but the final product to the planer may be losing value in grade out turns or volume due to trimming or down grading for excess skip.

Chasing recovery in the optimizer may not be the best value to the mill. In today’s market the demand for low grade lumber is very low and the price reflects that, making the spread in value more significant.

It may be worth losing some recovery to take a little more off the faces at the sawmill and make No.2btr lumber. Replacing a $200 piece of lumber in a lug with a $400 piece equates to a 100% gain in value as does replacing an 8’ piece with a 16’ piece of the same dimension and grade.

Each lug in the sawmill has a maximum potential value associated with it and that’s what should be chased to maximize profits. Log costs and inbound volumes of fiber don’t change with improved recovery, they just “look” better on paper when your LRF is higher, but the same volume of logs is entering the mill and costing you the same amount of money regardless of what you recover from them in the process of manufacturing them into lumber.

Stay tuned for more tips in next month’s blog post.

Robert – Process Expert