Sawing Under Control

Sawyer’s skill and experience combined with the modified Saw Control system means a better saw and superior product at MacMillan Bloedel’s Somass cedar mill.

By Jean Sorensen

Life at MacMillan Bloedel’s Somass cedar mill at Port Alberni just got easier for the sawyers this year. The reason is an adapted and upgraded version of the Saw Control system, which takes away much of the daily stress sawyers encounter.
 
The mill has also taken the Saw Control system to new heights. The system is linked directly to the computer controlling the carriage feed speed. Somass is also running the system with two probes on the bandsaw – rather than one, which is most common – to gain more detailed information on how the saw is performing both at the top and bottom edges of the cut.
 
The new 200 CF package has three basic elements: a more refined ability to monitor deviation; the Maximizer tied to the carriage; and a comprehensive history and trending package. “We think we will be able to give the sawyer a better saw,” says Brubaker. Plus, the sawyer will have to make less critical decisions, or, fewer of them.
 
MORE SCIENTIFIC CONTROL
The new Saw Control system tracks the saw while cutting, gauges saw performance, and determines whether to step up or down the carriage speed. The sawyer no longer has to gain almost a sixth-sense of whether the saw is in danger of jumping out of the cut. Should a problem arise, the system automatically cuts back on the carriage feed speed. When there is a wood problem, the system can step up or down to correct it, working on the deviation input. Also, if the sensors see that the saw is able to handle more wood, it steps the feed speed up to increase production
 
Bandsaws are now coming back to the fileroom in better shape, and the mill expects to save money both from reduced maintenance and repair times as well as a longer saw life.
 
The result has been two-fold: an increase in lineal throughput and a system that can process wood faster than a human can, which means less stress and more productivity. As well, the system can look at what is happening with the saws, to optimize carriage speed and thus reduce the number of off-cuts and increase the saw quality, two elements that allow for smoother relationships and less finger-pointing between the file-room and the sawyer’s booth.
 
The system was installed in May 1997, Brubaker says, and at first sawyers were “hesitant” to use it. The core of the system was really an upgrade of the existing Maximizer system, moving it from analog to digital. On the old system, the sawyer had two warning lights, one indicating snaking and the second indicating that the deviation was moving to the point of being dangerous. The system was useful but only as a guide, and hands-on sawyers tended not to use it too much, relying instead on their instincts to determine when the snaking was occurring.
 
But since the system was modified, Brubaker says that sawyers are happy with the upgrade. After a start-up debugging phase, sawyers now use the system all the time. “The only time they have it off is when I have requested it,” he says, checking the screen on his computer, which has a software program showing how the system is performing on each breakdown line.
 
The system does take a bit of getting used to. Brubaker has one written-off bandsaw to prove it, although he admits he has to chalk it up to human error. The sawyer encountered difficulties in a log and tried to compensate by manually backing the saw out of the cut and replacing it. However, the saw snagged and tore. If the operator had let the system’s self-correcting abilities kick in rather than try to take control, the problem would have been resolved, Brubaker believes.
 
Aside from that damaged bandsaw, Brubaker says, the bandsaws coming back to the fileroom are in better shape. In the long term, this is expected to save money in a number of ways.
 
Saw life is expected to be extended as there will be less abuse during sawing. Maintenance and repair times are expected to be cut and the blades will suffer less wear and tear.
 
While the system does eliminate much of the sawyer’s decision-making, it does not replace it. The sawyer can over-ride it and increase speed even if the system is at the top of the speed curve, or decrease it if the sawyer sees a problem that the saws haven’t.
 
LOG SUPPLY CHANGES
Brubaker’s decision to convert to the new digital Saw Control system came after viewing it at Dunkley Forest Products in northern B.C. Moreover, MacMillan Bloedel needed to get better at cutting the lower grade cedars that were moving into the mill. Brubaker liked the Dunkley package, but adds that what “intrigued me was the history and trending programs.” He liked the ability to follow the performance and maintenance history of each saw, using Excel 97 on his own PC.
 
By optimizing carriage feed speed and thus throughput via a direct computer link between the Saw Control system and the carriage drive, the mill hopes to help offset its reduced and lower-grade log supply and thus maintain output.
 
This historical data will be invaluable, he maintains, not only to see which saws fall down on the job, but to find out which ones succeed. He can examine how the treatment of these saws differed from those that had more problems. The sawfilers will use the system for measuring both short-and long-term results when corrections are being made. Modifications to a saw can be traced immediately to determine how they affect the saw’s performance, while the long-term effect of those modifications on the saw’s life can also be assessed to make sure that short-term gains are not being paid for by long-term pain.
 
The data collected on the saw for both sawing accuracy and historical trending is done by two probes, top and bottom. On the 9-foot CAE double pass system, which can saw 61 feet, the two guides, placed 8 feet apart, can follow both edges of the saw and determine whether one is off-center of the cut on the large, old growth timber that is being milled.
 
At the same time that the Somass mill’s fibre base has been reduced, the market for cedar is up. With a limited fibre supply, deviation can be costly in terms of spoilt product. Yet cedar has inherent cutting problems, including a natural acidity. “The high acid content leads to dulling of the sawblades,” says Brubaker. Dulling not only slows the cutting process, but increases friction – and thus snaking – and further affects the saw’s performance.
 
The affect of species on the saw’s performance can be tracked by the digital deviation system. A mainframe terminal sits in the fileroom (a top light flashes to indicate any sawing problems) and, at a touch of a button, sawfilers can track saws. If any look unsatisfactory or if the maintenance department encounters a problem pn a particular saw, the sawfiler can get a printout of the saw’s cutting performance on that shift to see how many times it deviated or came close to deviation.
 
CARRIAGE SPEED INCREASED
Brubaker’s desire to speed up the carriage drive, done by Jacobsen Engineering of California, through connecting it directly to the Saw Control system was based on the mill’s new log supply realities. Material that once would have been deemed suitable for shingle bolts alone is now going into the mill, for a log diet with far more rotten cores and broken pieces. “Also a lot of the wood is not round, but half round,” says Brubaker, adding that the system has the ability to feed wood at 550 ft./ min. maximum if required.
 
The system simply links the carriage drive to the computer software system, which receives information from the guides on how effectively the saw is cutting. Deviation perimeters are programmed into the system and the carriage speeds up or backs down when it is not hitting those perimeters.
 
Here’s a thumbnail sketch of how it works: the Saw Control system assumes control of the saw as soon as the current transformers on the bandmill motor indicate that the saw is cutting. Once in the cut, sawing deviation is used to determine whether to speed up, hold, or slow down the carriage feed speed. There are four “up speeds” available, and the system will move one speed at a time, after a short pause, if the saw keeps cutting accurately. Once the cutting threshold has been reached, the system kicks into a hold pattern. If the saw deviates past a certain point, then the carriage shifts to slow-down mode. The degree of the slow-down corresponds to the deviation encountered. If a major dive occurs, the system is dropped to its slowest speed. The system has four “down speeds”, including the crash speeds.
 
MAINTENANCE
In the sawfiler’s room, the two most time-consuming elements are tensioning and benching. While Brubaker says there has been no noticeable effect on the tensioning time, leveling time has been reduced. “Generally the saws are coming off in better shape,” he says, adding that as more data is compiled on a daily basis per saw and placed into the history and trending package, more insight into the cost savings is gained.
 
Brubaker also expects to be able to keep a closer eye on efforts to improve saw performance, with less lead time between when the changes were made and the mill knows whether they have had positive results or not. When modifications are made to the sawblades – for example, Brubaker may wish to try a new tooth configuration – the system allows him to monitor what is going on in the cab of the sawyer, so he can see how the changes are affecting the cutting process almost immediately.
 
NO PANCREA
The system installed at Port Alberni has moved the computer sawing system into another dimension, as it optimizes saw carriage speeds to the material being cut. Tying the carriage into the carriage feed-speed and initiating a response to under-feeding or over-feeding is a critical step in improving sawmill production and quality. But, as Brubaker says, while it identifies problems, it does not solve them.
For example, the system will identify that deviation is happening and identify the need to reduce speed. But, it does not specify the root cause, and that’s where the human element comes in. Interpretation of the data being collected is still key.
 
“Sometimes we come away with more questions than answers,” Brubaker says. But then that’s where all great discoveries start.