MAINTAINING CONTROL

By John Hebert

Manufacturing lumber is a relatively straightforward process; cutting a tree length log to the required lengths, breaking down to recover as much lumber as possible, by using computerized scanning and chipping heads or sawing.

There are many factors that come into play when processing the log into lumber; From bucking, scanning, positioning, sawing, sorting, drying, planing, sorting again (by grade) and ultimately, shipping to the customer.

During the process of cutting the log to length, control must be maintained to make accurate cuts and prevent damage to the saw. Whether it is a device such as a log stop, or a clamping jaw or dogs, the log should not twist, drop, or move against the side of the saw. Obviously the result will be inaccurate bucking and worse yet damage to the saw and potential for saw breakage.

When a log is scanned, positioned with log turners, and held in position with press rolls then sent through a canter, a very accurate feed system and setworks is critical. If the log moves during the chipping or sawing process, the result will be a mis-manufactured cant that is twisted, bowed or have a side that has not been touched.  If the cant has a  “wavy or snaky” pattern, or moves during sawing on a bandmill, extreme pressure will be put on the saw and guides, leading the saw to heat up very quickly and most likely “dish” or distort the saw to the point that it will no longer cut accurately.

Feed rolls on a bandmill must be manufactured perfectly concentric to also prevent movement of the piece while cutting. Attention should also be made that the feed rolls be kept clean of pitch build up, causing an out-of-round condition. This may cause the piece of lumber being cut to move; creating the appearance of snaking, or being cut too thin due to excessive pitch buildup.

The same can also apply to gang or board edgers; with pitch buildup, damaged or worn knurls, faulty bearings, the piece being cut may lead or pull to one side while being cut. Occasionally infeed and outfeed rolls are higher than the feed rolls inside the saw box.  All of these are conditions that can and will cause the lumber to pull or move against the saw and guides.  Creating high stresses and heat build up will lead to saw / guide failure, mis-manufacture of lumber and sawmill downtime.

The purpose of all press rolls and feed rolls are to control the positive feed of material through a machine center. Slack feed chains need to be adjusted and press rolls must be kept in good condition, especially in frozen conditions.  During the winter months when the sapwood in the tree freezes, the material being cut becomes very hard to control. When sawing a cant in any gang edger, there is a tremendous amount of energy applied to the saws and cant being sawn. If control is not maintained, the cant will be shot through the saws at a dangerously high rate of speed and will splinter on impact. Many times the cant will not make it all the way through the saws and jam. Frustrated sawfilers and millwrights too often work an hour or more, with chainsaws and wedges to break apart the jammed block of wood, to remove the damaged saws and guides.

If aggressive press or feed rolls are sharp and downward pressure is high, damage to the edges or face of boards is common. Depending on thickness and width of the board, severe edge crush or press roll dimples on the face of the lumber, due to aggressive rolls, often will not dress out at the planer downgrading valuable lumber.

Communication and timing of computerized equipment must be adjusted and monitored by tradesmen and operators on a regular basis, to keep lumber flow smooth and efficient. Software upgrades should also be installed on PLC’s and scanning systems to maintain as up to a date system as possible.

If control of a piece of log or lumber being handled whether it is bucked, scanned, canted, sawn, sorted, planed etc. is lost, ultimately the result will be lost revenue.

 If you have any comments, ideas or questions of interest regarding the sawfiling trade that we can use in this column, please send me an e-mail; jehebert@telus.net

   John Hebert is the Head Filer at Gorman Bros. Lumber in Westbank, BC.