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.