(Editor’s Note: In his regular column, Alan Froome continues his discussion of sawmill ideas and methods and how they evolved, along with a review of some recent developments in technology. This series of columns is intended to be a generic overview of different methods used in the sawmill industry in response to readers’ requests.)
Following the previous articles discussing the processes used to produce rough lumber, boards, cants, etc., we now come to the final stage in the lumber manufacturing process: planing it smooth or converting it to a variety of mouldings. We also introduce the reader to the terminology used in the process. Of course, not every mill planes lumber; some sell lumber products as rough sawn only. Different and unique methods are used from region to region and from mill to mill.
Planer Mill Design
Rough sawn lumber is cut in the sawmill to sizes that include a ‘planing allowance.’ This is the small surface allowance that is removed later by planing to give the accurate, finished size and smooth finish to lumber.
Softwood planing mills have steadily evolved to become very high-speed operations. They usually are located and run separately from the sawmill that supplies them with lumber. In fact, sometimes they are supplied by more than one sawmill.
The hardwood industry usually refers to the planing process as ‘surfacing.’ Surfaced hardwood blanks often are sold ‘as is’ and go through a final finishing process to make flooring, furniture components, and other products.
Planer Mill Flow
After drying, stacks of lumber are transferred to a planer mill. The lumber is singulated by a tilt break-down hoist and the stickers separated for re-use later.
Nowadays the lumber usually passes transversely on lugged deck chains over a moisture detector, and some pieces may be rejected and dropped out of the line for re-stacking. These degrade pieces may be remanufactured later or sold as lower grade lumber. The good boards continue along to the end of the transfer deck system, where they move onto a high-speed belt conveyor. They are further accelerated end-ways by a ‘pineapple’ feeder into the planer or planer-matcher.
A planer-matcher has profile heads
to produce exact sizes and patterns. Some of these machines also can split wide boards into two narrow boards – such as splitting a 2×8 into two 2×4,
for example.
Feed speeds have gradually increased. Some softwood mill planers run at 2,000 feet per minute. To reduce high-pitched noise, the planer is usually located in a sound-insulated room of its own.
The planer cutting action is designed to leave a smooth finish on both sides of the wood with little or no knife marks. A common rule of thumb is to use one planer knife per 50 feet per minute of feed speed. The cutting angle of each knife will vary, depending on the wood species. It is not uncommon for a planer to be equipped with 24 knife heads.
The idea behind the design of the planer feed system is to send the pieces through the planer butt to butt. The machine takes a thin cut off both sides, and the boards emerge onto a landing table, which in turn feeds a transfer deck for grading.
Grading is usually done manually, although there are systems available that can perform automatic grading with scanners and computers. Manual grading at today’s rapid piece count speeds is a challenge if not almost impossible, so the grading process is being automated more and more.
Even internal x-ray grading units are at work in some planing mills to reveal internal wood defects, and some mills use Machine Stress Rating (MSR) machines. MSR machines have rollers to perform a mechanical bending test on each board. As the board passes through, it is also labeled with a color or code to identify its strength rating.
Radiata pine has notoriously wide strength variables, depending whether it is pith (heartwood) wood or outer sapwood. Some mills in Australia build roof trusses with radiata pine, using the color coded MSR labels to assemble pieces for appropriate components.
Grading is followed by sorting, often with a tray sorter, which causes less
damage to the finished lumber, before stacking it into packages. Strapping and
wrapping follow in many mills for weather protection.
Making Moulding
As part of the finishing process, some mills use a planer-moulder instead of a planer-matcher in order to process lumber into different mouldings. These can include baseboards, door and window casing, crown moulding, chair rail moulding, tongue and groove panels, and more. Lower value species, like imported radiata pine from Chile or New Zealand, often are converted into moulding. On the West Coast, hemlock is often used for this purpose. A moulder machine differs from a planer in that it has a continuously adjustable lower bedline through the machine.
Small Business
Most moulding machines have profile cutters top and bottom. They can be changed quickly to run small orders. The simpler machines can also be fairly inexpensive, which is one reason that many small operators get into the wood products business by first producing mouldings.
One contractor in Texas recently found a local market for aromatic tongue and groove red cedar, which is used for closet linings and decorative wall treatments in new homes. After trying to do it in his spare time, using two routers and a single-side planer, he purchased a four-sided planer-moulder. What took him eight minutes per board before now only takes him 30 seconds, and he has a growing business.
Another type of remanufacturing process suited to small businesses is production of dowels. Small diameter rough logs, with the bark on, can be converted directly to smooth, round dowels for fencing and other products using a machine called a dowel mill. It works somewhat like a big pencil sharpener and produces round dowels from 2-6 inches in diameter from rough logs up to 9 inches in diameter. Larger machines are also available. Since dowels produced from small diameter logs in this process contain both sapwood and heartwood, they are stronger and less likely to twist in the sun compared to 4×4 timbers or plywood peeler cores – which are all heartwood — that are processed into poles.
