Moving blade = Dollar Yield pick up - a little background

The conversation about just how important or effective is the use of a moving blade ripsaw is really not a new one. In the earliest days of ripping very large boards, usually pine, a company called Portland Iron Works developed a saw that used very mechanical components to maximize the rip yields of boards that were often more than 2 FEET wide! In those days, a large percentage of the common household mouldings were manufactured by several large moulding producers on the US West coast and these high volume producers knew the importance of getting the maximum number of moulding blanks from every board. The Portland saws (PIW’s) were roll fed saws which meant that a board could be “pinched” against a fence with a canted roll feed system and all the rip blanks would have the same geometry as the original board. This system allowed for minimizing the edge loss of what we now call a dipchain designed feed system. More on this later. The PIW saws used a very simple keypunch system which allowed the operator to move a bank of laser lights across a board that was positioned on transfer chain system in in front of the operator. The transfer station also had a board flipper that gave the operator the option of seeing both sides of the boards where he used a “trial and error” method of determining where the blades should be positioned to best utilize the board. By casting a laser light on the board in advance of actually making a cut, the operator could avoid splitting a knot or other defect and putting defects in two piece instead of just one. He would also be able to position the blades to take the widest and usually most valuable pieces as often as possible and equally important, getting the highest number useable pieces out of each board. When the operator was satisfied he had the best solution, he fenced the board in cue and a pneumatically controlled set of cylinders moved each of several blades to the assigned position and ripped the board. The older PIW’s were a bit slow due the time it took to singulate the boards, make the decisions, move the boards into the fence position and then into the saw. In spite of the extra time required, the increase in yield was more valuable than a higher production volume with its associated waste. Through the years, the PIW saws became more sophisticated incorporating new control technologies allowing solutions to be “latched” to boards so 3,4, or 5 boards could be evaluated and cued in front of the saw for improved throughput. Cutting speeds were improved and the saws became very productive. Because these saws were roll fed, they were mostly used on softwood applications where the more pliable species responded consistently to being forced against a fence while being cut. Generally speaking, hardwood species are not pliable enough to be referenced or “pinched” against a fence and are therefore not suitable for the roll feed style machines. Because of the tendency of hardwoods to be resistant to fencing as a reference, it became necessary to develop a gang ripsaw that acted like the classic single straightline ripsaw. The earliest dipchain multiple ripsaws were considered “fixed arbor” where the sawblades were mounded on an arbor or sleeve where the blade to blade relationship was in a fixed configuration. By mounting the blades on a solid arbor with fairly large spacers forming the “pockets” or blank dimension, the saws provided excellent dimensional accuracy and the ability to produce high volumes of rip blanks. But because these saws did not use a fence but created a reference by accurately driving the board through the cutting chamber in a straightline (the term borrowed from the earliest single straightline ripsaws) a significant amount of edge waste was being developed in the process. This edge waste or “edgings” discussion has become the focus of many evaluations of rough mill efficiency From these early beginnings the conversation has persisted as to just how much more effective is moving the blades to a new configuration for each board? In other words, does a moving blade saw system out perform a fixed arbor saw system significantly enough to justify the cost? And how much additional equipment is required to actually get the benefits of a moving blade saw system.