From our mill-yard stockpile, logs are brought from the log decks to sawmill entrances by a wheeled log loader. The oversize logs that are too big for mainstream sawmill equipment have their own entrance to the sawmill where they are cut into custom order products by the head rig. Cut-to-length logs are fed into the sawmill at a different area, and the small and medium sized tree-length logs are continuously hauled to the Prentice, a stationary machine with a grapple that advances the logs to the feed troughs, at a third entrance.
If we follow a tree length log through the sawmill process starting at the primary log entrance to the mill, we would see what looks like a big mechanical arm and hand working to sort the logs. This machine, called the Prentice, sorts the tree-length logs into two lines; the smaller logs are sorted to feed into a 22” debarker, and the medium ones into a 35″ debarker. The debarkers have spinning knives inside that strip the bark off the log. The log then enters the sawmill and the bark, which falls into a conveyor, is transported to the hog plant, which will be explained later.
Inside the mill the debarked logs are scanned every 16th of an inch with a laser system that sends information to computers and monitors in the cut off saw booth. The computer system can be programmed to make choices on the best cut patterns for the greatest utilization and value from the log. The log is ready for its first cut at the cut off saws. The two separate lines each have a cut off saw that is a 6 foot diameter vertical saw. The small log line is controlled manually by the cut off saw operator to deal with the inconsistent nature of small wood. The saws on the larger line, however, are programmed to make cuts based on the computer made decisions for getting the best value from the log. Automatic photo-eyes at 8, 10, 12, 14, and 16 foot intervals control the stops and ensure the log is in the proper position for cutting. Once in position, the log is clamped by rollers to ensure it will not move and it is cut.
Following the cut off saws, the logs are sorted into decks (or bins) according to their diameter to facilitate a better and more consistent flow of logs through the mill. Logs of the same or similar dimensions can be fed from one deck and the machines they are fed into have only minor adjustments to make.
The decks that hold the larger logs are fed into the canterline and the decks that hold smaller logs are fed into the small log line (also known as the Hewsaw or peewee line). Log singulators in the form of step feeders or log ladders individualize logs for processing so they feed one at a time onto a conveyor with an equal distance between each log.
Logs being fed into the canterline are laser scanned and the information is used to compute the optimal cuts. The log is then rotated by red spike rollers into the best position for processing the log, determined by the computer. The log is scanned a second time to ensure proper cutting alignment or the computer will make a readjustment to the cut pattern. The chipping heads and saw-box move into place as a pattern is cut out of the bottom of the log so it cannot change position. Feed rolls hold the log in position as it enters the chipping heads where the other three sides are chipped off to leave a “cant”, which is a four-sided block of wood. If the log is a larger one, two side boards will also be cut from the log and they will be processed through the board edger.
The board edger, as the name suggests, puts a square edge on the side boards that have come from the canterline, or on lumber that has been re-routed from other areas for further refinement. The wood that is edged off a board is sent to the chipper and made into wood chips, which are sold for pulp and paper production.
The cants that have come off the canterline are set up on queuing decks to go to one of two gang saws. The first gang is the double arbour gang which has 20 vertical saws set approximately 2 inches apart; a cant goes in and lumber comes out. The second gang is called the 5/4 gang and it works on the same principles as the double arbour gang except that the distance between its saws can be adjusted to manage custom order sizes.
If the logs coming out of the cut off saws were sorted into the decks holding the small logs, they will be fed into the HEWSAW; what we call our small log line. This machine curve saws logs by turning them so the curve is down (like a banana with its two points in the air) and pivoting them lengthwise through the machine following the centre of the log. Four sides are chipped off and the remaining fibre will either be one piece of lumber or big enough to be cut into 2, 3 or 4 pieces of lumber. This is a single-pass curve-sawing machine from log to lumber. The woodchips are conveyed away to the chip shaker and sifted through screens to ensure they meet size specifications and then travel on to the chip bins. The other screened whitewood particles form part of the hogfuel biomass (to be explained later).
At the trim saws, all of the boards from the canterline and the small line merge. Operators at the trim saw queuing deck manipulate the boards so that every board can be scanned using computerized ‘true shape scanning’ to detect length, width, thickness and physical defects. If there are “bad” edges or wane, the board can be sent back to the board edger to be edged once more or remanufactured from a two inch board to a one inch board. If the board meets specifications and makes it through the remanufacturing reject gate, it will be trimmed at the appropriate useable length. Inside the trim saw machine, one or more of nine saws can cut at any two foot interval. The trim ends are sent to the chipper.
Because the boards have been scanned, the computer has the information necessary to sort every board according to its dimensions into one of sixty bins in the J-bar sorter. When a bin is full, the operator is alerted by a red light and the bin can be lowered to floor chains running below. The chains then deliver the boards to the stacker.
The stacker lays out a number of boards (the number depends on the board dimensions) horizontally on a hydraulic table that elevates and lowers. A set of strips is placed on top of the boards and between each added layer of boards to facilitate the drying process and to allow air to circulate evenly to each individual board. The table lowers as each layer is arranged on top until the bundle is full and the table is at its lowest point. The bundle can now be transferred out of the building on chains. This ‘green’ bundle, which means it still has a high moisture content, approximately 40 percent moisture content, is now ready to be removed from the sawmill building and dried.